definition of knowledge essay

Overview – The Definition of Knowledge

The definition of knowledge is one of the oldest questions of philosophy. Plato’s answer, that knowledge is justified true belief , stood for thousands of years – until a 1963 philosophy paper by philosopher Edmund Gettier challenged this definition.

Gettier described two scenarios – now known as Gettier cases – where an individual has a justified true belief but that is not knowledge.

Since Gettier’s challenge to the justified true belief definition, various alternative accounts of knowledge have been proposed. The goal of these accounts is to define ‘knowledge’ in a way that rules out Gettier cases whilst still capturing all instances of what we consider to be knowledge.

A Level philosophy looks at 5 definitions of knowledge :

• Justified true belief (the tripartite definition)
• JTB + No false lemmas

Reliabilism

Virtue epistemology, infallibilism.

It’s important to first distinguish the kind of knowledge we’re discussing here. Broadly, there are three kinds of knowledge:

• Ability: knowledge how – e.g. “I know how to ride a bike”
• Acquaintance: knowledge of – e.g. “I know Fred well”
• Propositional: knowledge that – e.g. “I know that London is the capital of England”

When we talk about the definition of knowledge, we are talking about the definition of propositional knowledge specifically.

Justified True Belief

The tripartite definition.

In Theaetetus , Plato argues that knowledge is “true belief accompanied by a rational account”. This got simplified to:

‘Justified true belief’ is known as the tripartite definition of knowledge.

Necessary and sufficient conditions

The name of the game in defining ‘knowledge’ is to provide necessary and sufficient conditions.

For example, ‘unmarried’ and ‘man’ are both necessary to be a ‘bachelor’ because if you don’t meet both these conditions you’re not a bachelor. Further, being an ‘unmarried man’ is sufficient to be a ‘bachelor’ because everything that meets these conditions is a bachelor. So, ‘unmarried man’ is a good definition of ‘bachelor’ because it provides both the necessary and sufficient conditions of that term.

The correct definition of ‘knowledge’ will work the same way. Firstly, we can argue that ‘justified’, ‘true’, and ‘belief’ are all necessary for knowledge.

For example, you can’t know something if it isn’t true . If someone said, “I know that the moon is made of green cheese” you wouldn’t consider that knowledge because it isn’t true.

Similarly, you can’t know something you don’t believe. It just wouldn’t make sense, for example, to say “I know today is Monday but I don’t believe today is Monday.”

And finally, justification . Suppose someone asks you if you know how many moons Pluto has. You have no interest in astronomy but just have a strong feeling about the number 5 because it’s your lucky number or whatever. You’d be right – Pluto does indeed have 5 moons – but it seems a bit of a stretch to say you knew Pluto has 5 moons. Your true belief “Pluto has 5 moons” is not properly justified and so would not count as knowledge.

So, ‘justified’, ‘true’, and ‘belief’ may each be necessary for knowledge. But are these conditions sufficient? If ‘justified true belief’ is also a sufficient definition of knowledge, then everything that is a justified true belief will be knowledge. However, this is challenged by Gettier cases .

Problem: Gettier cases

Gettier’s paper describes two scenarios where an individual has a justified true belief that is not knowledge. Both scenarios describe a belief that fails to count as knowledge because the justified belief is only true as a result of luck .

Gettier case 1

• Smith and Jones are interviewing for the same job
• Smith hears the interviewer say “I’m going to give Jones the job”
• Smith also sees Jones count 10 coins from his pocket
• Smith thus forms the belief that “the man who will get the job has 10 coins in his pocket”
• But Smith gets the job, not Jones
• Then Smith looks in his pocket and, by coincidence, he also has 10 coins in his pocket

Smith’s belief “the man who will get the job has 10 coins in his pocket” is:

• Justified: he hears the interviewer say Jones will get the job and he sees that Jones has 10 coins in his pocket
• True: the man who gets the job (Smith) does indeed have 10 coins in his pocket

This shows that the tripartite definition of knowledge is not sufficient : you can have a justified true belief that is not knowledge.

Gettier case 2

Gettier’s second example relies on the logical principle of disjunction introduction (or, more simply, addition ).

Disjunction introduction says that if you have a true statement and add “or some other statement” then the full statement (i.e. “true statement or some other statement”) is also true.

For example: “London is the capital of England” is true. And so the statement “either London is the capital of England or the moon is made of green cheese” is also true, because London is the capital of England. Even though the second part (“the moon is made of green cheese”) is false, the overall statement is true because the or means only one part has to be true (in this case “London is the capital of England”).

Gettier’s second example is as follows:

• Smith has a justified belief that “Jones owns a Ford”
• So, using the principle of disjunctive introduction above, Smith can form the further justified belief that “Either Jones owns a Ford or Brown is in Barcelona”
• Smith thinks his belief that “Either Jones owns a Ford or Brown is in Barcelona” is true because the first condition is true (i.e. that Jones owns a Ford)
• But it turns out that Jones does not own a Ford
• However, by sheer coincidence, Brown is in Barcelona

So, Smith’s belief that “Either Jones owns a Ford or Brown is in Barcelona”   is:

• True: “Either Jones owns a Ford or Brown is in Barcelona” turns out to be true. But Smith thought it was true because of the first condition (Jones owns a Ford) whereas it turns out it is true because of the second condition (Brown is in Barcelona)
• Justified: The original belief “Jones owns a Ford” is justified, and so disjunction introduction means that the second belief “Either Jones owns a Ford or Brown is in Barcelona” is also justified.

But despite being a justified true belief, it is wrong to say that Smith’s belief counts as knowledge, because it was just luck that led to him being correct.

This again shows that the tripartite definition of knowledge is not sufficient .

Alternative definitions of knowledge

Gettier cases are a devastating problem for the tripartite definition of knowledge .

In response, philosophers have tried to come up with new definitions of knowledge that avoid Gettier cases.

Generally, these new definitions seek to refine the justification condition of the tripartite definition. True and belief remain unchanged.

JTB + no false lemmas

The no false lemmas definition of knowledge aims to strengthen the justification condition of the tripartite definition.

It says that James has knowledge of P if:

• James believes that P
• James’s belief is justified
• James did not infer that P from anything false

So, basically, it adds an extra condition to the tripartite definition . It says knowledge is justified true belief + that is not inferred from anything false (a false lemma).

This avoids the problems of Gettier cases because Smith’s belief “the man who will get the job has 10 coins in his pocket” is inferred from the false lemma “Jones will get the job” .

• The tripartite definition says Smith’s belief is knowledge, even though it isn’t
• The no false lemmas response says Smith’s belief is not knowledge, which is correct.

So, in this instance, the no false lemmas definition appears to be a more accurate account of knowledge than the tripartite view: it avoids saying Gettier cases count as knowledge.

Problem: fake barn county

However, the no false lemmas definition of knowledge faces a similar problem: the fake barn county situation:

• In ‘fake barn county’, the locals create fake barns that look identical to real barns
• Henry is driving through fake barn county, but he doesn’t know the locals do this
• These beliefs are not knowledge , because they are not true – the barns are fake
• This time the belief is true
• It’s also justified by his visual perception of the barn
• And it’s not inferred from anything false.

According to the no false lemmas definition, Henry’s belief is knowledge.

But this shows that the no false lemmas definition must be false. Henry’s belief is clearly not knowledge – he’s just lucky in this instance.

Reliabilism says James knows that P if:

• James’s belief that P is caused by a reliable method

A reliable method is one that produces a high percentage of true beliefs.

So, if you have good eyesight, it’s likely that your eyesight would constitute a reliable method of forming true beliefs. If you have an accurate memory, it’s likely your memory would also be a reliable method for forming true beliefs. If a website is consistent in reporting the truth, that website would also count as a reliable method.

But if you form a belief through an unreliable method – for example by simply guessing or using a biased source – then it would not count as knowledge even if the resultant belief is true.

Children and Animals

An advantage of reliabilism is that it allows for young children and animals to have knowledge. Typically, we attribute knowledge to young children and animals. For example, it seems perfectly sensible to say that a seagull knows where to find food or that a baby knows when its mother is speaking.

However, pretty much all the other definitions of knowledge considered here imply that animals and young children can not have knowledge. For example, a seagull or a baby can’t justify its beliefs and so justified true belief rules out seagulls and young babies from having knowledge. Similarly, if virtue epistemology is the correct definition, it is hard to see how a seagull or a newly born baby could possess intellectual virtues of care about forming true beliefs and thus possess knowledge.

However, both young children and animals are capable of forming beliefs via reliable processes, e.g. their eyesight, and so according to reliabilism are capable of possessing knowledge.

You can argue against reliabilism using the same fake barn county argument above : Henry’s true belief that “there’s a barn” is caused by a reliable process – his visual perception. Reliabilism would thus (incorrectly) say that Henry knows “there’s a barn” even though his belief is only true as a result of luck.

There are several forms of virtue epistemology (we will look at two), but common to all virtue epistemology definitions of knowledge is a link between a belief and intellectual virtues . Intellectual virtues are somewhat analogous to the sort of moral virtues considered in Aristotle’s virtue theory in moral philosophy . However, instead of being concerned with moral good, intellectual virtues are about epistemic good. For example, an intellectually virtuous person would have traits such as being rational, caring about what’s true, and a good memory.

Linda Zagzebski: What is Knowledge?

Formula for creating gettier-style cases.

Philosopher Linda Zagzebski argues that definitions of knowledge of the kind we have looked at so far (i.e. ‘true belief + some third condition ’) will always fall victim to Gettier-style cases. She provides a formula for constructing such Gettier cases to defeat these definitions:

• E.g. Henry’s belief “there’s a barn” when he is looking at the fake barns
• E.g. Henry’s belief “there’s a barn” when he is looking at the one real barn
• In the second case, the belief will still fit the definition (‘true belief + some third condition ’) because it’s basically the same as the first case
• But the second case won’t be knowledge, because it’s only true due to luck

Zagzebski argues that this formula will always provide a means to defeat any definition of knowledge that takes the form ‘true belief + some third condition’ (whether that third condition is justification , formed by a reliable process , or whatever).

The reason for this is that truth and the third condition are simply added together, but not linked  ( the belief is not apt , to use Sosa’s terminology ). The fact that truth and the third condition are not linked leaves a gap where lucky cases can incorrectly fit the definition.

Zagzebski’s definition of knowledge

The issues resulting from the gap between truth and the third condition motivate Zagzebski to do away with the ‘truth’ condition altogether. Instead, Zagzebski’s analysis of knowledge is that James knows that P if:

• James’s belief that P arises from an act of intellectual virtue

However, in Zagzebski’s analysis of knowledge, the ‘truth’ of the belief is kind of implied by the idea of an act of intellectual virtues. This can be shown by drawing a comparison with moral virtue :

An act of moral virtue is one where the actor both intends to do good and achieves that goal. For example, intending to help an old lady across the road but killing her in the process is not an act of moral virtue because it doesn’t achieve a virtuous goal (despite the virtuous intent). Likewise, helping the old lady across the road because you think she will give you money is not an act of moral virtue – even though it succeeds in achieving a virtuous goal – because your intentions aren’t good.

Intellectual virtue is similar: You must both have the correct motivation (e.g. you want to find the truth) and succeed as a result of that virtue (i.e. your belief turns out to be true because you acted virtuously).

Virtues motivate us to pursue what is good. In the case of knowledge, good knowledge is also true. Secondly, virtues enable us to achieve our goals (in the same way a virtuous i.e. good knife enables you to cut) and so intellectual virtues would enable you to reliably form true beliefs.

Sosa’s virtue epistemology

Another virtue epistemology approach to knowledge is Ernest Sosa’s definition of apt belief .

Sosa uses the following analogy to argue that knowledge, like a virtuous shot in archery, has the following three properties: Accuracy , adroitness , and aptness .

Returning to the fake barn county example , Sosa’s virtue epistemology could (correctly) say Henry’s belief “there’s a barn” in fake barn county would not qualify as knowledge – despite being true and formed by a reliable method – because it is not apt . Yes, Henry’s belief is accurate (i.e. true) and adroit (i.e. Henry has good eyesight etc.), but he only formed the true belief as a result of luck, not because he used his intellectual virtues.

Problem: children and animals

As mentioned in more detail in the reliabilism section above , a potential criticism of virtue epistemology is that it appears to rule out the possibility of young children or babies possessing knowledge, despite the fact that they arguably can know many things.

Infallibilism argues that for a belief to count as knowledge , it must be true and justified in such a way as to make it certain .

So, even though Smith has good reasons for his beliefs in the Gettier case , they’re not good enough to provide certainty . Certainty, to philosophers like Descartes, means the impossibility of doubt .

In the Gettier case, Smith might have misheard the interviewer say he was going to give Jones the job. Or, even more extreme, Smith might be a brain in a vat and Jones may not even exist! Either of these scenarios – however unlikely – raise the possibility of doubt.

Problem: too strict

So, infallibilism correctly says Smith’s belief in the Gettier case does not count as knowledge.

But it also says pretty much everything fails to qualify as knowledge!

“I know that water boils at 100 ° c” – can this be doubted? Of course it can! Your science teachers might have been lying to you, you might have misread your thermometer, you might be a brain in a vat and there’s no such thing as water!

So, whereas Gettier cases show the tripartite definition to set the bar too low for knowledge, infallibilism sets the bar way too high – barely anything can be known! In other words, we can argue that certainty is not a necessary condition of knowledge.

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1.3: The Concept of Knowledge

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• Page ID 22243
• Jeffery L. Johnson
• Portland State University via Portland State University Library

So when a man gets hold of the true notion of something without an account, his mind does truly think of it, but he does not know it, for if he cannot give and receive an account of a thing, one has no knowledge of that thing. But when he has also got hold of an account, all this becomes possible to him and he is fully equipped with knowledge.

—PLATO1

Definitions and Word Games

Suppose that we are concerned with the question of economic justice—the fact that a few are ridiculously wealthy, while many are pitifully poor. We might convene an academic conference to discuss the issue and suggest some sort of coherent social policy. Economists might tell us about how income distribution is empirically related to national productivity. Political scientists might tell something about relative tax rates and the amount of government services. Sociologists could address the social effects of long-term poverty. Historians could give us some sense of whether the problem is better or worse than it was a hundred years ago. It would not be at all surprising if a philosopher contributed a paper on the meaning of economic justice. In one way, such a contribution seems necessary and foundational. After all, how can we reasonably construct some social policy aimed at greater economic justice if we are not crystal clear as to what we mean by this concept? In another light, however, the philosopher’s contribution seems frivolous and even counterproductive. If there is wide agreement that there is a problem that needs to be solved, the philosopher’s concern with long-dead thinkers such as Plato, Adam Smith, and Marx may strike us as an irresponsible waste of time and intellectual energy. To carry this example just a bit further, suppose the philosopher’s paper offers a definition of economic justice that suggests some kind of tension with other widely held values and social policies and goes so far as to suggest that we will never have a concept of economic justice that everyone will feel comfortable with. Now the philosopher’s concern with theory and the definition of terms may strike us as subversive. It may be difficult and controversial to articulate a theory about the nature of economic justice that everyone will agree with. Nevertheless, we know injustice when we see it. And to suggest that we spend our time defining terms and teasing out subtle philosophical arguments rather than offering constructive solutions to the obvious problems that plague our society is both dangerous and immoral. But all this is quite unfair. No sane philosopher is going to suggest that we spend all our time and energy in academic theoretical pursuits. Obviously, there are crises that call for immediate action, and we all recognize the need to make decisions on less than perfect information. But there is also a need for abstract theoretical work. It does seem crazy to propose significant social changes that will affect all of us without some kind of clear understanding of what we are trying to bring about. Pausing to reflect on the nature of economic justice—defining our terms, as they say—may be worthwhile even in a time of some urgency.

Please excuse the above digression. I have included it because I believe that many beginning students see much of traditional epistemology in the same uncharitable light that our philosopher was portrayed. Every reader of this book is a mature speaker of English. The verb to know and the abstract noun knowledge are fairly normal words within the English language. Obviously, we must know what they mean. We will discover, however, that it proves exceedingly difficult to articulate a clear and coherent definition, or theory, of knowledge.

The Myth of Definition

This chapter discusses the prospects for offering a helpful analysis, or definition, of the concept of knowledge. As a starting point, we need to take a little time dispelling a common misunderstanding about the importance of definition in everyday contexts, as well as philosophical contexts. It is widely believed that people do not know the meaning of the words they use—they do not know what they are talking about—unless they can provide adequate definitions for all those words. This is simply a mistaken view of meaning.

Someone can be an excellent athlete—a hitter in baseball, for example—yet be a very poor coach or teacher of how to hit. Surprisingly, perhaps, others can be mediocre hitters but turn into outstanding hitting coaches. The reason these things are possible is that there is all the difference in the world between doing something and describing, or explaining, how to do something. Think for a moment about those things that you are most skilled at doing—shooting free throws, playing a musical instrument, riding a bicycle, and so on. How confident would you be that you could teach someone else how to be skillful at these activities? Could you write a manual for them on how to do any one of these?

Speaking a language is much more like hitting a baseball than being a good hitting coach. Language is a skillful activity that human beings master with remarkable facility in ways that philosophers, psychologists, and linguists are only beginning to appreciate. I can safely assume that any reader of this book is an accomplished enough user of English that you know full well the meaning of almost every word that philosophers have spent a great deal of time and energy trying to analyze or define. You all know the meaning of terms such as beauty , justice , and knowledge because you can use sentences such as the following to communicate with other English speakers.

• 1. That’s a beautiful painting.
• 2. Simple justice demands that all the kids get to play.
• 3. You don’t really know that the Dodgers will win the pennant; you just hope they will.

All this is important because it is so easy to forget in the middle of philosophical battles. We are going to analyze the concept of knowledge in this chapter. We will see that this task is difficult, controversial, and perhaps in the end, impossible to complete satisfactorily. This doesn’t mean for a second that you or the great minds of Western philosophy do not know how to use words such as know and knowledge for the purposes of clear communication.

The Need for Conceptual Clarity

Although I stand 100 percent behind what I said previously, this doesn’t mean that careful conceptual analysis is not important. People sometimes make remarkable claims about knowledge. We have just seen how the skeptic can put together plausible and disturbing arguments that we know next to nothing. The arguments of the last chapter are classical examples of the sorts of intellectual concerns that occupy the attention of professional philosophers. Disputes about knowledge are not limited to philosophers, however. We often hear that modern scientists do not know that evolution by natural selection is true. Many claim that it is only a “theory.” This is sometimes backed up with an argument. Science, so this line of thinking goes, is only concerned with what can be directly observed or proved with laboratory experiments. But evolution, it is sometimes claimed, cannot be directly observed, both because it is too slow of a process and because the most interesting observations would have needed to take place in a time before there were human observers. Furthermore, creationists claim that no controlled laboratory experiment can prove that evolution is true.

If we are to make any progress in understanding, let alone resolving, these kinds of intellectual disputes, we are going to need to be much clearer in our own minds as to what counts as knowledge. I claim to know that I am at my computer composing this chapter. The skeptic tells me I don’t know this after all; it might only be a dream. I am quite sure that I know that natural selection is true. Creationists claim that I don’t and that my “faith” in the theory is no different from religious belief. How can we possibly hope to make progress toward resolving these disputes without some fairly specific agreement as to what counts as genuine knowledge?

For some, the kind of conceptual analysis in which we engage in this chapter can be fun and exciting in its own right. Most of you, however, should see it as a necessary means to an end. I assume most of you care about whether scientists know what they are talking about. If you are like I am, you think they probably do. But to really feel confident about this, you need to have some answers to the philosophical skeptic who says it might all be a dream and the procedural skeptic who argues from a specific model of scientific knowledge to doubt about things such as evolution and climate change. To answer either of these skeptics productively, you need some agreement about the nature of knowledge.

Knowledge and Belief

Human beings seem to be a very credulous species; we believe an amazing variety of things. Our ancestors believed in witches, that the earth was flat, and in the divine right of kings. People today believe that their futures are foretold in horoscopes, that good writing can be accomplished in first drafts, and that their favorite sports team will finally get it together. From the perspective of history, it is easy to find countless beliefs that we sincerely held that strike us as foolish, dangerous, and immoral. But of course, not all beliefs fit into this category.

Other things we don’t merely believe, we know. I, of course, believe that I am a philosophy professor, a one-time softball player, and a husband to a beautiful woman. But I don’t just believe these things, I know them. The distinction between belief and knowledge is not like the one between being a sibling and being an only child—it is not an exclusive, either/or difference. It is rather like the distinction between an automobile and a convertible. To be a convertible is to be a special kind of automobile. As logicians put it, being an automobile is a necessary condition of being a convertible. Not all automobiles are convertibles, but all convertibles are automobiles.

Traditional models, or definitions, of knowledge have attempted to articulate a list of necessary conditions that are jointly sufficient for having genuine knowledge. The abstract noun knowledge is kind of artificial. I think we will do better to use the more familiar verb. Our observations about knowing and believing suggest the first entry on our list of necessary conditions:

There is a fairly common way of talking that seems to call this into question. Suppose we have a friend who is headed for heartache partly because he refuses to take seriously the obvious evidence of his lover’s infidelity. We might say, “Jake knows that she’s untrue, but he can’t bring himself to believe it.” Or perhaps we have a colleague who is foolishly refusing to take heed of medical symptoms: “Sarah knows something is wrong but just won’t believe it.” How seriously should we take the claim that both Jake and Sarah have knowledge but lack belief? Not very.

Jake sees the obvious signs and has his moments of doubt. Sarah too. If they didn’t, we wouldn’t be inclined to say they knew. It is, of course, possible for people to be perversely dense. People can be totally oblivious to things that are perfectly obvious to others. Connie may genuinely believe that her lover is totally faithful despite the lame excuses and the lipstick on his collar. But we would never be tempted to say Connie knows this, though perhaps she should. When we use the “knows but doesn’t believe” idiom, we are getting at something interesting about Jake and Sarah. They seem to be engaging in what philosophers call self-deception. This is an important issue in both philosophy and psychology but really says nothing about how to define knowledge.

I take it to be settled that knowledge implies some kind of genuine conviction or intellectual confidence. Thus the first necessary condition of knowledge turns out to be relatively secure, uncontroversial, and philosophically straightforward. Would that we could say the same about the conditions to follow.

The Search for the Truth

You are the district attorney, and you’ve got a great case. The defendant is the kind of lowlife that society needs to do something about. You’ve got the goods on him too, lots of physical evidence, a clear motive, and witnesses. The case will be an easy one to try, and it will be a feather in your cap to be the one who put him away. You just “know” that the slime ball’s guilty. There’s only one problem with this scenario; the guy didn’t do it. It does not matter how sincere your belief is nor how good the evidence seems to be—if what you thought you knew turns out to be false, it’s back to the drawing board. Truth is an absolute precondition for knowledge. Unfortunately, truth is a philosophical mess.

Contemporary philosophy is about as far from consensus about the nature of truth as any issue in the field. Some believe that truth is correspondence with reality. Others believe that it is coherence with other widely held beliefs. Yet others claim that the assertion that “snow is white is true” is just a fancy way of saying that “snow is white.” All these theories of truth have plausible arguments in their defense, and all suffer from serious conceptual problems. Professional philosophy doesn’t know what truth is. I don’t know what it is either, but I will nevertheless say a little more about truth toward the end of this book.

In spite of all the confusion about the nature of truth, however, the relationship between truth and knowledge is as clear as could be. The only beliefs that we have that are viable candidates for being knowledge are those that are true. The surest way to defeat someone’s claim that they know something is to show that what they claim to know is false. This suggests a work-around epistemological definition of truth:

Admittedly, this is a pretty trivial definition. It does, however, have the advantage of separating philosophical disputes about the nature of truth from the noncontroversial connection between truth and knowledge.

Thus truth supplies a second necessary condition for knowledge. We can expand our evolving model of knowledge as follows:

Epistemic Justification

Perhaps we already have all that we need. The concept of knowledge seems both subjective and objective. To believe something is to be in a certain cognitive state that individual “subjects” find themselves in or fail to find themselves in. For that belief to be true (or not-false) it must be dependent on things entirely independent of those subjects—the way things “objectively” are. Condition i takes care of the subjective element, and ii covers the objective. What more do we need?

I have been hoping for a raise. Unfortunately, my latest evaluation left a lot to be desired, and the state’s budget looks pretty bleak. Forever the optimist, I continue to think the best. I woke up yesterday and as I was having my morning coffee I glanced at my horoscope. The entry for Pisces was way cool: “You will receive something long overdue and well deserved. All the signs are positive.” My raise! What could be clearer? I went to work with a smile on my face absolutely confident that I would get the good news. And I did! The governor decided that all state employees should get a modest salary adjustment, and that afternoon, we were all formally notified.

The two conditions for knowledge are satisfied. Johnson believes that he will get a raise, and it is true that he will get a raise. Does he therefore know that he will get a raise? Most of us would be very reluctant to say he possesses knowledge. What he believes turns out to be true but merely by coincidence or good luck. The subjective element of belief and the objective element of truth seem much too tenuously connected. What seems to be missing is some reason or evidence in support of my belief. Sure, the horoscope is a reason in the sense of providing a psychological explanation for why I happen to have this belief. But it’s such a poor reason—it’s so unreliable—that we attribute the belief’s truth to good fortune and not the strength of the reason.

Epistemologists have adopted the idiom of normative obligation to get at the stronger connection between belief and truth that is required for genuine knowledge. You are entitled to claim knowledge, according to this way of thinking about things, only if your belief is justified —that is, just in case you have very good reason for thinking it is true. Thus on the so-called standard analysis of knowledge a third necessary condition of knowledge, one that completes the package and makes it jointly sufficient, is the justification condition.

What Does It Take to Be Justified?

We have seen how skeptics can produce a formidable battery of arguments designed to show that we are never completely justified in believing anything. The problem concerns the connection between truth and justification. The only standard that completely eliminates the possibility of our beliefs being held in error is one of self-evidence or certainty. But as the Cartesian project has convinced most of us, epistemological certainty is unattainable. This means that whatever model of knowledge is finally endorsed will be committed to some sort of epistemic fallibility. This is not that serious a worry for most natural or social scientists but does run counter to the dominant tradition in Western epistemology.

Self-evidence and certainty may have set unrealistically high standards for knowledge, but these epistemic standards had the superficial appearance of being clear and identifiable. Models of knowledge that substitute criteria for epistemic justification must be prepared to state some new criterion for distinguishing unfounded belief from a promising theory and from established knowledge. The contemporary literature offers many intriguing possibilities—some highly formal and some quite commonsensical—but none that have won anything approaching consensus.

I suggest that we understand the idea of epistemic justification in terms of evidence. The things that we know are those true beliefs for which we have very, very, very good evidence—what a lawyer calls proof beyond a reasonable doubt. Good evidence is something that we are all familiar with and something that we can learn to reliably spot. I will be offering in the chapters to follow a model of—or a kind of formula for testing for—good evidence. I hope to convince you that this model captures almost everything we care about when we assess the quality of a person’s evidence or for that matter, their claims to knowledge.

Let’s transform the standard analysis of knowledge in light of all this into the following:

An Unsolved Problem

If you were reading very carefully, you may have noticed a slight difference in the way I stated the standard analysis of knowledge at the end of preceding section and the section immediately before that one. You are all smart enough to see the obvious change in condition iii , but can you find the other difference? The way the philosophic tradition has defined knowledge is to articulate necessary and sufficient conditions for knowing something. The standard analysis of knowledge claims that the three necessary conditions are, taken together, sufficient for knowing something. In my statement of a “transformed” analysis, I wimped out a bit. I claimed that my three conditions were all necessary—that’s what the “only if” signifies—but I left it open whether the three conditions were sufficient. Here’s why.

Consider the following little thought experiment. My wife and I have spent the last hour collaborating on our special spaghetti sauce. Just as we are getting ready to serve dinner, we discover that we are out of Parmesan cheese. We divide responsibilities—she will toss the salad and serve dinner; I’ll make the emergency run to the store. While at the store, I meet a colleague doing research in contemporary epistemology—she wants an example of knowledge. I suggest that I know there is a spaghetti dinner sitting on our dining room table right now. And as luck would have it, it’s true that a spaghetti dinner is on the table. I believe it, it’s true, and I’m justified in believing it. All is well. Well, maybe not. After I left, our German shepherd, Guido, got rambunctious and knocked the pot of simmering spaghetti sauce on the dirty kitchen floor. My wife considered violence against the dog, but before anything could happen, a neighbor arrived with a pot of leftover spaghetti sauce, announcing that she was leaving on vacation and it would surely spoil before she returned. Thus the spaghetti sauce that made my knowledge claim true is unconnected to the spaghetti sauce that provided the justification for my belief. It is odd in the extreme to claim that I had knowledge of the pot of spaghetti sitting on my table. It is pure serendipity that my belief turned out to be true.

A lot of contemporary epistemology has been concerned with ruling out these kinds of “Guido” cases (actually, they are called Gettier examples, after the philosopher who first made them famous). Many philosophers have suggested that some fourth or fifth or sixth and so on condition must be added to our analysis of knowledge. I am not sure whether I personally agree. To be on the safe side, however, I will be content with the above transformed analysis. The epistemic action in this little book will focus on condition iii anyway. What the heck is it to have evidence or good evidence or exceedingly good evidence for something?

• 1. What is the myth of definition? Does it show that the traditional philosophical quest of defining terms (analyzing them) is unnecessary? Why, or why not?
• 2. Explain why having a true belief that something is the case is not good enough for claiming to know that it is the case.
• 3. What does the “Guido” example show us about knowledge?

Here’s something I claim to know: climate change (global warming) is very real and very dangerous. How would the epistemological skeptic respond to this? Given the view of knowledge defended in this chapter, what would need to be true if my knowledge claim is correct?

1. Plato, “Theatetus,” in Plato: The Collected Dialogues , trans. F. M. Cornford (Princeton, NJ: Princeton University Press, 1961), 909.

• September 22, 2011

The Knowledge Problem

Studying knowledge is one of those perennial topics—like the nature of matter in the hard sciences—that philosophy has been refining since before the time of Plato. The discipline, epistemology, comes from two Greek words episteme (επιστημη) which means knowledge and logos (λογος) which means a word or reason. Epistemology literally means to reason about knowledge. Epistemologists study what makes up knowledge, what kinds of things can we know, what are the limits to what we can know, and even if it’s possible to actually know anything at all.

Coming up with a definition of knowledge has proven difficult but we’ll take a look at a few attempts and examine the challenges we face in doing so. We’ll look at how prominent philosophers have wrestled with the topic and how postmodernists provide a different viewpoint on the problem of knowledge. We’ll also survey some modern work being done in psychology and philosophy that can help us understand the practical problems with navigating the enormous amounts of information we have at our disposal and how we can avoid problems in the way we come to know things.

Do We Know Stuff?

In order to answer that question, you probably have to have some idea what the term “know” means. If I asked, “Have you seen the flibbertijibbet at the fair today?” I’d guess you wouldn’t know how to answer. You’d probably start by asking me what a flibbertijibbet is. But most adults tend not to ask what knowledge is before they can evaluate whether they have it or not. We just claim to know stuff and most of us, I suspect, are pretty comfortable with that. There are lots of reasons for this but the most likely is that we have picked up a definition over time and have a general sense of what the term means. Many of us would probably say knowledge that something is true involves:

• Certainty – it’s hard if not impossible to deny
• Evidence – it has to based on something
• Practicality – it has to actually work in the real world
• Broad agreement – lots of people have to agree it’s true

But if you think about it, each of these has problems. For example, what would you claim to know that you would also say you are certain of? Let’s suppose you’re not intoxicated, high, or in some other way in your “right” mind and conclude that you know you’re reading an article on the internet. You might go further and claim that denying it would be crazy. Isn’t it at least possible that you’re dreaming or that you’re in something like the Matrix and everything you see is an illusion? Before you say such a thing is absurd and only those who were unable to make the varsity football team would even consider such questions, can you be sure you’re not being tricked? After all, if you are in the Matrix, the robots that created the Matrix would making be making you believe you are not in the Matrix and that you’re certain you aren’t.

What about the “broad agreement” criterion? The problem with this one is that many things we might claim to know are not, and could not be, broadly agreed upon. Suppose you are experiencing a pain in your arm. The pain is very strong and intense. You might tell your doctor that you know you’re in pain. Unfortunately though, only you can claim to know that (and as an added problem, you don’t appear to have any evidence for it either—you just feel the pain). So at least on the surface, it seems you know things that don’t have broad agreement by others.

These problems and many others are what intrigue philosophers and are what make coming up with a definition of knowledge challenging. Since it’s hard to nail down a definition, it also makes it hard to answer the question “what do you know?”

What is Knowledge?

As with many topics in philosophy, a broadly-agreed-upon definition is difficult. But philosophers have been attempting to construct one for centuries. Over the years, a trend has developed in the philosophical literature and a definition has emerged that has such wide agreement it has come to be known as the “standard definition.” While agreement with the definition isn’t universal, it can serve as a solid starting point for studying knowledge.

The definition involves three conditions and philosophers say that when a person meets these three conditions, she can say she knows something to be true. Take a statement of fact: The Seattle Mariners have never won a world series.  On the standard definition, a person knows this fact if:

• The person believes the statement to be true
• The statement is in fact true
• The person is justified in believing the statement to be true

The bolded terms earmark the three conditions that must be met and because of those terms, the definition is also called the “tripartite” (three part) definition or “JTB” for short. Many many books have been written on each of the three terms so I can only briefly summarize here what is going on in each. I will say up front though that epistemologists spend most of their time on the third condition.

First, beliefs are things people have. Beliefs aren’t like rocks or rowboats where you come across them while strolling along the beach. They’re in your head and generally are viewed as just the way you hold the world (or some aspect of the world) to be. If you believe that the Mariners never won a world series, you just accept it is as true that the Mariners really never won a world series. Notice that accepting that something is true implies that what you accept could be wrong. In other words, it implies that what you think about the world may not match up with the way the world really is. This implies that there is a distinction between belief and truth . There are some philosophers—notably postmodernists and existentialists—who think such a distinction can’t be made which we’ll examine more below. But in general, philosophers claim that belief is in our heads and truth is about the way the world is. In practical terms, you can generally figure out what you or someone else believes by examining behavior. People will generally act according to what they really believe rather than what they say they believe—despite what Dylan says .

Something is true if the world really is that way. Truth is not in your head but is “out there.” The statement, “The Mariners have never won a world series” is true if the Mariners have never won a world series. The first part of that sentence is in quotes on purpose. The phrase in quotes signifies a statement we might make about the world and the second, unquoted phrase is supposed to describe the way the world actually is. The reason philosophers write truth statements this way is to give sense to the idea that a statement about the world could be wrong or, more accurately, false (philosophers refer to the part in quotes as a statement or proposition ). Perhaps you can now see why beliefs are different than truth statements. When you believe something, you hold that or accept that a statement or proposition is true. It could be false that’s why your belief may not “match up” with the way the world really is. For more on what truth is, see the Philosophy News article, “ What is Truth? ”

Justification

If the seed of knowledge is belief, what turns belief into knowledge? This is where justification (sometimes called ‘warrant’) comes in. A person knows something if they’re justified in believing it to be true (and, of course, it actually is true). There are dozens of competing theories of justification. It’s sometimes easier to describe when a belief isn’t justified than when it is. In general, philosophers agree that a person isn’t justified if their belief is:

• a product of wishful thinking (I really wish you would love me so I believe you love me)
• a product of fear or guilt (you’re terrified of death and so form the belief in an afterlife)
• formed in the wrong way (you travel to an area you know nothing about, see a white spot 500 yards away and conclude it’s a sheep)
• a product of dumb luck or guesswork (you randomly form the belief that the next person you meet will have hazel eyes and it turns out that the next person you meet has hazel eyes)

Because beliefs come in all shapes and sizes and it’s hard to find a single theory of justification that can account for everything we would want to claim to know. You might be justified in believing that the sun is roughly 93 million miles from the earth much differently than you would be justified in believing God exists or that you have a minor back pain. Even so, justification is a critical element in any theory of knowledge and is the focus of many a philosophical thought.

People-centered Knowledge

You might notice that the description above puts the focus of knowing on the individual. Philosophers talk of individual persons being justified and not the ideas or concepts themselves being justified. This means that what may count as knowledge for you may not count as knowledge for me. Suppose you study economics and you learn principles in the field to some depth. Based on what you learn, you come to believe that psychological attitudes have just as much of a role to play in economic flourishing or deprivation as the political environment that creates economic policy. Suppose also that I have not studied economics all that much but I do know that I’d like more money in my pocket. You and I may have very different beliefs about economics and our beliefs might be justified in very different ways. What you know may not be something I know even though we have the same evidence and arguments in front of us.

So the subjective nature of knowledge partly is based on the idea that beliefs are things that individuals have and those beliefs are justified or not justified. When you think about it, that makes sense. You may have more evidence or different experiences than I have and so you may believe things I don’t or may have evidence for something that I don’t have. The bottom line is that “universal knowledge” – something everybody knows—may be very hard to come by. Truth, if it exists, isn’t like this. Truth is universal. It’s our access to it that may differ widely.

Rene Descartes and the Search for Universal Knowledge

A lot of people are uncomfortable with the idea that there isn’t universal knowledge. Philosopher Rene Descartes (pronounced day-cart) was one of them. When he was a young man, he was taught a bunch of stuff by his parents, teachers, priests and other authorities. As he came of age, he, like many of us, started to discover that much of what he was taught either was false or was highly questionable. At the very least, he found he couldn’t have the certainty that many of his educators had. While many of us get that, deal with it, and move on, Descartes was deeply troubled by this.

One day, he decided to tackle the problem. He hid himself away in a cabin and attempted to doubt everything of which he could not be certain. Since it wasn’t practical to doubt every belief he had, Descartes decided that it would be sufficient to subject the foundations of his belief system to doubt and the rest of the structure will “crumble of its own accord.” He first considers the things he came to believe by way of the five senses. For most of us these are pretty stable items but Descartes found that it was rather easy to doubt their truth. The biggest problem is that sometimes the senses can be deceptive. And after all, could he be certain he wasn’t insane or dreaming when he saw that book or tasted that honey? So while they might be fairly reliable, the senses don’t provide us with certainty—which is what Descartes was after.

Unfortunately, this left Descartes with no where to turn. He found that he could be skeptical about everything and was unable to find a certain foundation for knowledge. But then he hit upon something that changed modern epistemology. He discovered that there was one thing he couldn’t doubt: the fact that he was a thinking thing. In order to doubt it, he would have to think. He reasoned that it’s not possible to doubt something without thinking about the fact that you’re doubting. If he was thinking then he must be a thinking thing and so he found that it was impossible to doubt that he was a thinking being.

This seemingly small but significant truth led to his most famous contribution to Western thought: cogito ergo sum (I think, therefore I am). Some mistakenly think that Descartes was implying with this idea that he thinks himself into existence. But that wasn’t his point at all. He was making a claim about knowledge. Really what Descartes was saying is: I think, therefore I know that I am.

The story doesn’t end here for Descartes but for the rest of it, I refer you to the reading list below to dig deeper. The story of Descartes is meant to illustrate the depth of the problems of epistemology and how difficult and rare certainty is, if certainty is possible—there are plenty of philosophers who think either that Descartes’ project failed or that he created a whole new set of problems that are even more intractable than the one he set out to solve.

Postmodernism and Knowledge

Postmodern epistemology is a growing area of study and is relatively new on the scene compared with definitions that have come out of the analytic tradition in philosophy. Generally, though, it means taking a specific, skeptical attitude towards certainty, and a subjective view of belief and knowledge. Postmodernists see truth as much more fluid than classical (or modernist) epistemologists. Using the terms we learned above, they reject the idea that we can ever be fully justified in holding that our beliefs line up with the way the world actually is. We can’t know that we know.

Perspective at the Center

In order to have certainty, postmodernists claim, we would need to be able to “stand outside” our own beliefs and look at our beliefs and the world without any mental lenses or perspective . It’s similar to wondering what it would be like to watch ourselves meeting someone for the first time? We can’t do it. We can watch the event of the meeting on a video but the experience of meeting can only be had by us. We have that experience only from “inside” our minds and bodies. Since its not possible to stand outside our minds, all the parts that make up our minds influence our view on what is true. Our intellectual and social background, our biases, our moods, our genetics, other beliefs we have, our likes and dislikes, our passions (we can put all these under the label of our “cognitive structure”) all influence how we perceive what is true about the world. Further, say the postmodernists, it’s not possible to set aside these influences or lenses. We can reduce the intensity here and there and come to recognize biases and adjust for them for sure. But it’s not possible to completely shed all our lenses which color our view of things and so it’s not possible to be certain that we’re getting at some truth “out there.”

Many have called out what seems to be a problem with the postmodernist approach. Notice that as soon as a postmodernist makes a claim about the truth and knowledge they seem to be making a truth statement! If all beliefs are seen through a lens, how do we know the postmodernists beliefs are “correct?” That’s a good question and the postmodernist might respond by saying, “We don’t!” But then, why believe it? Because of this obvious problem, many postmodernists attempt to simply live with postmodernist “attitudes” towards epistemology and avoid saying that they’re making claims that would fit into traditional categories. We have to change our perspective to understand the claims.

Community Agreement

To be sure, Postmodernists do tend to act like the rest of us when it comes to interacting with the world. They drive cars, fly in airplanes, make computer programs, and write books. But how is this possible if they take such a fluid view of knowledge? Postmodernists don’t eschew truth in general. They reject the idea that any one person’s beliefs about it can be certain. Rather, they claim that truth emerges through community agreement. Suppose scientists are attempting to determine whether the planet is warming and that humans are the cause. This is a complex question and a postmodernist might say that if the majority of scientists agree that the earth is warming and that humans are the cause, then that’s true. Notice that the criteria for “truth” is that scientists agree . To use the taxonomy above, this would be the “justification condition.” So we might say that postmodernists accept the first and third conditions of the tripartite view but reject the second condition: the idea that there is a truth that beliefs need to align to a truth outside our minds. 

When you think about it, a lot of what we would call “facts” are determined in just this way. For many years, scientists believed in a substance called “phlogiston.” Phlogiston was stuff that existed in certain substances (like wood and metal) and when those substances were burned, more phlogiston was added to the substance. Phlogiston was believed to have negative weight, that’s why things got lighter when they burned. That theory has since been rejected and replace by more sophisticated views involving oxygen and oxidation.

So, was the phlogiston theory true? The modernist would claim it wasn’t because it has since been shown to be false. It’s false now and was false then even though scientists believed it was true. Beliefs about phlogiston didn’t line up with the way the world really is, so it was false. But the postmodernist might say that phlogiston theory was true for the scientists that believed it. We now have other theories that are true. But phlogiston theory was no less true then than oxygen theory is now. Further, they might add, how do we know that oxygen theory is really the truth ? Oxygen theory might be supplanted some day as well but that doesn’t make it any less true today.

Knowledge and the Mental Life

As you might expect, philosophers are not the only ones interested in how knowledge works. Psychologists, social scientists, cognitive scientists and neuroscientists have been interested in this topic as well and, with the growth of the field of artificial intelligence, even computer scientists have gotten into the game. In this section, we’ll look at how work being done in psychology and behavioral science can inform our understanding of how human knowing works.

Thus far, we’ve looked at the structure of knowledge once beliefs are formed. Many thinkers are interested how belief formation itself is involved our perception of what we think we know. Put another way, we may form a belief that something is true but the way our minds formed that belief has a big impact on why we think we know it. The science is uncovering that, in many cases, the process of forming the belief went wrong somewhere and our minds have actually tricked us into believing its true. These mental tricks may be based on good evolutionary principles: they are (or at least were at some point in our past) conducive to survival. But we may not be aware of this trickery and be entirely convinced that we formed the belief in the right way and so have knowledge. The broad term used for this phenomenon is “cognitive bias” and mental biases have a significant influence over how we form beliefs and our perception of the beliefs we form. 1

Wired for Bias

A cognitive bias is a typically unconscious “mental trick” our minds play that lead us to form beliefs that may be false or that are directed towards some facts and leaving out others such that these beliefs align to other things we believe, promote mental safety, or provide grounds for justifying sticking to to a set of goals that we want to achieve. Put more simply, mental biases cause us to form false beliefs about ourselves and the world. The fact that our minds do this is not necessarily intentional or malevolent and, in many cases, the outcomes of these false beliefs can be positive for the person that holds them. But epistemologists (and ethicists) argue that ends don’t always justify the means when it comes to belief formation. As a general rule, we want to form true beliefs in the “right” way.

Ernest Becker in his important Pulitzer Prize winning book The Denial of Death attempts to get at the psychology behind why we form the beliefs we do. He also explores why we may be closed off to alternative viewpoints and why we tend to become apologists (defenders) of the viewpoints we hold. One of his arguments is that we as humans build an ego ( in the Freudian sense; what he calls “character armor”) out of the beliefs we hold and those beliefs tend to give us meaning and they are strengthened when more people hold the same viewpoint. In a particularly searing passage, he writes:

Each person thinks that he has the formula for triumphing over life’s limitations and knows with authority what it means to be a man [N.B. by ‘man’ Becker means ‘human’ and uses masculine pronouns as that was common practice when he wrote the book], and he usually tries to win a following for his particular patent. Today we know that people try so hard to win converts for their point of view because it is more than merely an outlook on life: it is an immortality formula. . . in matters of immortality everyone has the same self-righteous conviction. The thing seems perverse because each diametrically opposed view is put forth with the same maddening certainty; and authorities who are equally unimpeachable hold opposite views! (Becker, Ernest. The Denial of Death, pp. 255-256. Free Press.)

In other words, being convinced that our viewpoint is correct and winning converts to that viewpoint is how we establish ourselves as persons of meaning and significance and this inclination is deeply engrained in our psychological equipment. This not only is why biases are so prevalent but why they’re difficult to detect. We are, argues Becker and others, wired towards bias. Jonathan Haidt agrees and go so far as to say that reason and logic is not only the cure but a core part of the wiring that causes the phenomenon.

Anyone who values truth should stop worshipping reason. We all need to take a cold hard look at the evidence and see reasoning for what it is. The French cognitive scientists Hugo Mercier and Dan Sperber recently reviewed the vast research literature on motivated reasoning (in social psychology) and on the biases and errors of reasoning (in cognitive psychology). They concluded that most of the bizarre and depressing research findings make perfect sense once you see reasoning as having evolved not to help us find truth but to help us engage in arguments, persuasion, and manipulation in the context of discussions with other people. (Haidt, Jonathan. The Righteous Mind: Why Good People Are Divided by Politics and Religion (p. 104). Knopf Doubleday Publishing Group.)

Biases and Belief Formation

Research in social science and psychology are uncovering myriad ways in which our minds play these mental tricks. For example, Daniel Kahneman discusses the impact emotional priming has on the formation of a subsequent idea. In one study, when participants were asked about happiness as it related to their romantic experiences, those that had a lot of dates in the past would report that they were happy about their life while those that had no dates reported being lonely, isolated, and rejected. But then when they subsequently were asked about their happiness in general, they imposed the context of their dating happiness to their happiness in general regardless of how good or bad the rest of their lives seemed to be going. If a person would have rated their overall happiness as “very happy” when asked questions about general happiness only, they might rate their overall happiness as “somewhat happy” if they were asked questions about their romantic happiness just prior and their romantic happiness was more negative than positive.

This type of priming can significantly impact how we view what is true. Being asked if we need more gun control or whether we should regulate fatty foods will change right after a local shooting right or after someone suffers a heart scare. The same situation will have two different responses by the same person depending on whether he or she was primed or not. Jonathan Haidt relates similar examples.

Psychologists now have file cabinets full of findings on ‘motivated reasoning,’ showing the many tricks people use to reach the conclusions they want to reach. When subjects are told that an intelligence test gave them a low score, they choose to read articles criticizing (rather than supporting) the validity of IQ tests. When people read a (fictitious) scientific study that reports a link between caffeine consumption and breast cancer, women who are heavy coffee drinkers find more flaws in the study than do men and less caffeinated women. (Haidt, p. 98)

There are many other biases that influence our thinking. When we ask the question, “what is knowledge?” this research has to be a part of how we answer the question. Biases and their influence would fall under the broad category of the justification condition we looked at earlier and the research should inform how we view how beliefs are justified. Justification is not merely the application of a philosophical formula. There are a host of psychological and social influences that are play when we seek to justify a belief and turn it into knowledge. 2 We can also see how this research lends credence to the philosophical position of postmodernists. At the very least, even if we hold that we can get past our biases and get “more nearer to the truth,” we at least have good reason to be careful about the things we assert as true and adopt a tentative stance towards the truth of our beliefs.

In a day when “fake news” is a big concern and the amount of information for which we’re responsible grows each day, how we justify the beliefs we hold becomes a even more important enterprise. I’ll use a final quote from Haidt to conclude this section:

And now that we all have access to search engines on our cell phones, we can call up a team of supportive scientists for almost any conclusion twenty-four hours a day. Whatever you want to believe about the causes of global warming or whether a fetus can feel pain, just Google your belief. You’ll find partisan websites summarizing and sometimes distorting relevant scientific studies. Science is a smorgasbord, and Google will guide you to the study that’s right for you. (Haidt, pp. 99-100)

Making Knowledge Practical

Well most of us aren’t like Descartes. We actually have lives and don’t want to spend time trying to figure out if we’re the cruel joke of some clandestine mad scientist. But we actually do actually care about this topic whether we “know” it or not. A bit of reflection exposes just how important having a solid view of knowledge actually is and spending some focused time thinking more deeply about knowledge can actually help us get better at knowing.

Really, knowledge is a the root of many (dare I say most) challenges we face in a given day. Once you get past basic survival (though even things as basic as finding enough food and shelter involves challenges related to knowledge), we’re confronted with knowledge issues on almost every front. Knowledge questions range from larger, more weighty questions like figuring out who our real friends are, what to do with our career, or how to spend our time, what politician to vote for, how to spend or invest our money, or should we be religious or not, to more mundane ones like which gear to buy for our hobby, how to solve a dispute between the kids, where to go for dinner, or which book to read in your free time. We make knowledge decisions all day, every day and some of those decisions deeply impact our lives and the lives of those around us.

So all these decisions we make about factors that effect the way we and others live are grounded in our view of knowledge—our epistemology . Unfortunately few spend enough time thinking about the root of their decisions and many make knowledge choices based on how they were raised (my mom always voted Republican so I will), what’s easiest (if I don’t believe in God, I’ll be shunned by my friends and family), or just good, old fashioned laziness. But of all the things to spend time on, it seems thinking about how we come to know things should be at the top of the list given the central role it plays in just about everything we do.

Updated January, 2018: Removed dated material and general clean up; added section on cognitive biases. Updated March, 2014: Removed reference to dated events; removed section on thought experiment; added section on Postmodernism; minor formatting changes

• While many thinkers have written on cognitive biases in one form or another, Jonathan Haidt in his book The Righteous Mind and Daniel Kahneman in his book Thinking Fast and Slow have done seminal work to systemize and provide hard data around how the mind operates when it comes to belief formation and biases. There is much more work to be done for sure but these books, part philosophy, part psychology, part social science, provide the foundation for further study in this area. The field of study already is large and growing so I can only provide a thumbnail sketch of the influence of how belief formation is influenced by our mind and other factors. I refer the reader to the source material on this topic for further study (see reading list below). ↩
• For a strategy on how we can adjust for these natural biases that our minds seem wired to create, see the Philosophy News article, “ How to Argue With People ”. I also recommend Carol Dweck’s excellent book Mindset . ↩

For Further Reading

• Epistemology: Classic Problems and Contemporary Responses (Elements of Philosophy) by Laurence BonJour. One of the better introductions to the theory of knowledge. Written at the college level, this book should be accessible for most readers but have a good philosophical dictionary on hand.
• Belief, Justification, and Knowledge: An Introduction to Epistemology (Wadsworth Basic Issues in Philosophy Series) by Robert Audi. This book has been used as a text book in college courses on epistemology so may be a bit out of range for the general reader. However, it gives a good overview of many of the issues in the theory of knowledge and is a fine primer for anyone interested in the subject.
• The Theory of Knowledge: Classic and Contemporary Readings by Louis Pojman. Still one of the best books for primary source material. The edited articles have helpful introductions and Pojman covers a range of sources so the reader will get a good overview from many sides of the question. Written mainly as a textbook.
• The Stuff of Thought: Language as a Window into Human Nature   by Steven Pinker. While not strictly a book about knowledge per se, Pinker’s book is fun, accessible, and a good resource for getting an overview of some contemporary work being done mainly in the hard sciences.
• The Selections From the Principles of Philosophy by René Descartes . A good place to start to hear from Descartes himself.
• Descartes’ Bones: A Skeletal History of the Conflict between Faith and Reason by Russell Shorto. This book is written as a history so it’s not strictly a philosophy tome. However, it gives the general reader some insight into what Descartes and his contemporaries were dealing with and is a fun read.
• On Bullshit by Harry Frankfurt. One get’s the sense that Frankfurt was being a bit tongue-in-cheek with the small, engaging tract. It’s more of a commentary on the social aspect of epistemology and worth reading for that reason alone. Makes a great gift!
• On Truth by Harry Frankfurt. Like On Bullshit but on truth.
• A Rulebook for Arguments by Anthony Weston. A handy reference for constructing logical arguments. This is a fine little book to have on your shelf regardless of what you do for a living.
• Warrant: The Current Debate   by Alvin Plantinga. Now over 25 years old, “current” in the title may seem anachronistic. Still, many of the issues Plantinga deals with are with us today and his narrative is sure to enlighten and prime the pump for further study.
• Thinking Fast and Slow by Daniel Kahneman. The book to begin a study on cognitive biases.
• The Righteous Mind by Jonathan Haidt. A solid book that dabbles in cognitive biases but also in why people form and hold beliefs and how to start a conversation about them.
• The Denial of Death by Ernest Becker. A neo (or is it post?) Freudian analysis of why we do what we do. Essential reading for better understanding why we form the beliefs we do.
• Mindset: The New Psychology of Success by Carol S. Dweck. The title reads like a self-help book but the content is actually solid and helpful for developing an approach to forming and sharing ideas.

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1000-Word Philosophy: An Introductory Anthology

Philosophy, One Thousand Words at a Time

Epistemology, or Theory of Knowledge

Thomas Metcalf Category: Epistemology Word count: 999

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Many people think that they have a lot of knowledge. They also believe that other people sometimes know what they claim to know. But what is knowledge anyway? And how do we come to have it? Is it important that we have knowledge? If so, why?

The branch of philosophy that attempts to answer these and related questions is known as ‘epistemology’ or ‘theory of knowledge.’ [1]

1. What is Knowledge? [2]

One historically popular definition of ‘knowledge’ is the ‘JTB’ theory of knowledge: knowledge is j ustified, t rue b elief. [3] Most philosophers think that a belief must be true in order to count as knowledge. [4] Suppose that Smith is framed for a crime, and the evidence against Smith is overwhelming. But Smith is innocent. Does the jury know that Smith committed the crime ? No, because knowledge requires truth; the jury believed it, but they didn’t know it. [5]

Also, most philosophers think that the belief must be justified . We don’t normally consider a lucky guess to be knowledge. (If you flip a coin but don’t look at the result yet, and just find yourself believing that it’s Heads, and in fact it is Heads, we don’t think you knew that it was Heads.) Yet there is substantial debate about what justification is.

2. Analysis of Justification

What would be required to transform the lucky guess that the coin came up Heads into knowledge ? One standard answer is ‘justification.’ [6]

Intuitively, you would have to acquire good reason to believe that the coin came up Heads: for example, you look at the coin. [7] In general, theories of justification either say that the factors that justify your belief must be available within your own first-person, conscious experience, or that they don’t need to be. We call the former theories ‘internalist’ and the latter ‘externalist.’ [8]

For example, some internalists are evidentialists : roughly, they say that your justification depends on the evidence you have, for example the awareness of the image of a president’s head on a coin. And some externalists are reliabilists : roughly, they say that whether you are justified depends on whether your belief was formed by a reliable belief-forming mechanism, for example, the physical process of vision. For evidentialists, the evidence you have seems “internal” to your first-person awareness: it’s what you’re aware of. And whether the process that formed your belief is reliable seems “external” to your first-person awareness: you might not even have any beliefs about photons and how they work.

3. Sources of Knowledge and Evidence

We’ve thought about what it means to have justified beliefs. [9] But when our beliefs are in fact justified, what is the source or explanation of that justification?

Surely we get some justification from empirical observation : using our five senses, the tools of science, and introspection (looking inside your own mind, for example learning that you believe that 2+2=4). [10] This justification is ‘ a posteriori ’ or ‘empirical,’ for example, looking at the coin-toss result.

Maybe there is some knowledge that we acquire through intuition, definitions, or some other putative non -empirical evidence. We call this ‘ a priori ’ knowledge or justification: justified but independently of any particular empirical observation or awareness of the evidence or justification required. [11] I seem to know, just by thinking about it, that there can be no coins that are both square and circular; I don’t need to consult scientists. [12]

Roughly speaking, rationalists (about justification) believe that we have important, valuable a priori knowledge about the world, knowledge that’s not merely about the meanings of our words or concepts. Empiricists , in contrast, believe that all of our important knowledge of the world is empirical. [13]

Beyond this, feminist epistemologists have argued that one’s knowledge, and whether one is taken seriously as a knower, can depend on one’s particular social position, including one’s gender. [14] To the traditional list of sources of knowledge, we might add one’s standpoint and situation, and also add emotion. [15]

4. The Structure of Knowledge, Justification, and Inference

Normally, we think we can infer new beliefs from our existing beliefs: we believe some propositions, and on the basis of those beliefs, conclude that some other propositions are true.

If someone asks you to justify a belief, you’re likely to cite other beliefs you have. I know that Antarctica exists because I believe that maps are generally trustworthy and that maps claim that Antarctica exists. But can this regress of inference go on forever? [16]

One popular position is foundationalism . Foundationalists say that the regress stops at justified beliefs and, since the regress has stopped, those beliefs aren’t justified by any inference from any other belief. [17]

Another popular position is coherentism , according to which one’s beliefs are justified by being part of a web or network of coherent beliefs. [18]

We think a set of inferences can give us justified beliefs. But it’s possible to acquire false or unjustified beliefs, which wouldn’t be knowledge after all.

5. Skepticism

In general, skeptics deny that we have some item of knowledge. There are skeptics about whether we have:

• knowledge of the external world, i.e., the world beyond the contents of our conscious experiences; [19]
• moral knowledge; [20]
• religious knowledge; [21]
• knowledge from memory or knowledge of the past; [22]
• knowledge from induction; [23]
• scientific knowledge; [24] and
• knowledge of other minds. [25]

And some philosophers have endorsed global skepticism, according to which we have no knowledge or no justified beliefs at all. [26]

6. Other Issues

Epistemology is a broad field. Other issues include:

• the nature of perception; [27]
• the nature of understanding; [28]
• whether we should trust our peers when they disagree with us; [29]
• the relationships between epistemology, trust, and justice; [30]
• how different reasons for belief (not just epistemic reasons) should affect us or determine whether we have knowledge; [31]
• what value there is, if any, in having knowledge, especially in contrast to mere true belief; [32]
• whether ‘knowledge’ means the same thing in all contexts. [33]
• whether knowledge requires certainty; [34]
• whether philosophy should be continuous with, or even replaced by, science. [35]

And many more. [36]

7. Conclusion

Some philosophers believe that epistemology is “first philosophy,” fundamental to the rest of philosophy and inquiry, since all areas of study and learning seek understanding, justified beliefs, and knowledge. If they are correct, an understanding of at least the basics of epistemology is important for all thinking people. [37]

[1] In constructing this overview, I roughly follow online encyclopedias such as in Steup 2019 and Truncellito 2019 and textbooks such as BonJour 2002, Huemer 2002, and Steup and Sosa 2005. ‘Epistemology’ comes from Greek roots meaning the study of, or discourse about, knowledge.

[2] Here, we are talking about what’s sometimes called ‘propositional’ knowledge or ‘knowledge-that.’ But there are other mental facts about you that may count as your having knowledge. Someone might know how to ride a bicycle, or know what it’s lik e to taste lemon. These aren’t obviously propositional knowledge, but they are natural enough ways of using the term ‘knowledge.’

[3] Gettier (1963) attributes this conception or something very much like it to Plato ( Theaetetus 20 I; Meno 98), Chisholm (1957: 16), and Ayer (1956). BonJour (2002: 27) attributes a similar conception to Descartes. Yet as Gettier argues, there may be examples of justified, true beliefs that don’t count as ‘knowledge.’ Suppose that your computer has an error and its internal clock is stuck at 11:49 am. It stays this way all morning and you don’t notice. Then you happen to wonder what time it is, look at your computer’s clock, and see ‘11:49 am.’ Suppose, however, that the time actually just happens to be 11:49 am right when you look at the clock. Your belief that it is 11:49 am might be justified (because you have no reason yet to doubt your computer’s clock), and true (because you happened to check the clock right at 11:49 am), but many would say it doesn’t count as ‘knowledge.’ Therefore, perhaps there is some fourth property that a belief must have to count as knowledge. For more, see Zagzebski 1994 and Chapman 2014 (“ The Gettier Problem ” in 1000-Word Philosophy ).

[4] Sometimes a person might say, ‘I just knew I wasn’t going to get that job–but I did!’ But arguably, that use of ‘knew’ is intended to emphasize the person’s certainty, not to say that they really knew something false. But see Hazlett 2010 which argues that knowledge doesn’t require truth.

[5] And see n. 4.

[6] For an introduction to the concept of epistemic justification, see Epistemic Justification: What is Rational Belief? by Todd R. Long. Although the term of art for ‘whatever has to be added to true belief to create knowledge’ is ‘warrant.’ Cf. Plantinga 1993. Perhaps Gettier (1963) showed that warrant isn’t merely justification.

[7] See e.g. BonJour 2004: 5 on what epistemic justification is. Philosophers have described justification as occurring when a belief is likely to be true, or when a person who wants to have true beliefs ought to believe that belief, or when one has good reason to believe the belief, or when the belief is best-supported by the evidence. This question is actually fairly complex, however, because some (e.g. possibly Foley 1987: ch. 1; but see Kelly 2003 for critique) believe that epistemic justification is just a species of prudential or instrumental justification.

[8] I generally follow Pappas 2019; refer there for more information. In more detail: an internalist might say (as ‘accessibilists’ say) that justification depends on what you are aware of from the first-person perspective, or (as ‘mentalists’ say) on the current content of your mental states, or (as ‘evidentialists’ say) on the evidence available to you. Externalists might say (as ‘reliabilists’ say) that justification depends on one’s belief’s having been formed by a reliable belief-forming mechanism, or (as ‘proper functionalists’ say) by the proper functioning of your cognitive apparatus. Most generally, evidentialism, accessibilism, mentalism, and deontology are usually thought of as ‘internalist’ theories of epistemic justification, since they say your justification depends on factors internal to your mind or first-person awareness. And reliabilism, proper-functionalism, and virtue epistemology are normally thought of as ‘externalist’ theories of epistemic justification, since whether a belief was reliably formed, for example, may depend on factors you have no first-person access to. See e.g. Fumerton 1995 and BonJour and Sosa 2003, as well as Pappas 2019. One might also take the position that internalists and externalists are simply describing two different phenomena, both philosophically important, that are sometimes both referred to as ‘justification; cf. BonJour 2002: 233-7 and Pasnau 2013: 1008 ff. For more about specific internalist and externalist theories, see Conee and Feldman 2004 for evidentialism; Chisholm 1977: 17 for accessibilism; Conee and Feldman 2001 for mentalism; Alston 1989: 115-52 for deontology; Goldman 1979 for reliabilism; Plantinga 1993: 41 ff. and Bergmann 2006: ch. 5 for proper-functionalism; and Turri et al. 2019 for an introduction to virtue epistemology.

[9] One more note: There could be justified, false beliefs. For example, someone might do a really great job of framing you for a crime you didn’t commit, and so people would be justified in believing that you committed the crime, yet you really are innocent and so their justified belief is false. Such beliefs are part of the standard presentation of Gettier (1963) cases. Of course, a few philosophers have questioned whether justified or warranted false beliefs are possible (Sturgeon 1993; Merricks 1995).

[10] See for example Steup 2019: § 4.2. I assume that introspection is fundamentally empirical, at least in the sense necessary to make the a priori -empirical distinction most illuminating (BonJour 1998: 7).

[11] But not normally independent of any empirical observation at all. For example, we might need empirical observation to acquire the relevant concept in the first place. See e.g. BonJour 1998: 9.

[12] Perhaps moral knowledge, if it exists, is also a priori (cf. Huemer 2005). It’s difficult to imagine seeing, with my eyes , that stealing is wrong.

[13] Some famous rationalists include Plato, Descartes, and Leibniz; some famous empiricists include Locke, Berkeley, and Hume. Yet these categorizations aren’t 100% neat; for example, Locke and Berkeley are normally counted among the empiricists, but they may have made some limited room for a priori knowledge as well. See Markie 2019: § 1.2. Also, strictly speaking, when I talk about these different types of sentences, what I’m referring to is the distinction between analytic sentences ( very roughly, sentences that are true by definition, e.g. ‘all red squares are red’) and synthetic sentences (sentences that are not merely true by definition, e.g. ‘all red squares are somewhere on Earth’), such that rationalists believe in the synthetic a priori and empiricists don’t. For a general introduction to this debate, see Markie 2019.

[14] See Anderson 2020 for an overview.

[15] Jaggar 1988.

[16] Infinitists (e.g. Klein 1998) say that the regress goes back forever, but that our beliefs can still be justified.

[17] One of the most-important historical presentations of foundationalism is in Descartes (cf. Newman 2019: § 2.1). More-recent defenders include Pryor (2000) and Huemer (2001). Foundationalists face the challenge of explaining what could justify a belief other than an inference from some other belief. One answer that has received much attention recently is to appeal to some principle of conservatism; see e.g. Huemer 2001. Perhaps, for example, if it appears to you as if something is true, that appearance is enough to justify the belief.

[18] To say that these beliefs are coherent might mean, for example, that they are all logically consistent and mutually supporting. Thus for coherentists, in some sense, the regress of inference “circles back” on itself. Influential coherentists include Lewis (1946); Quine and Ullian (1970) and the early BonJour (1985). A more recent example is Poston (2014). Coherentists face their own challenges, for example, why there needs to be any “input” from outside one’s own mind (cf. BonJour 1985: ch. 6) in order to have a set of justified beliefs. Why isn’t mere coherence with the rest of one’s beliefs enough?

[19] See e.g. Descartes 1984 [1641]: 13.

[20] Sinnott-Armstrong 2020.

[21] Forrest 2020.

[22] Cf. Russell 2019 [1921]: 71-84.

[23] Hume 1896 [1739-40]: bk. I, part III, § VI.

[24] See e.g. Chakravartty 2019 for an overview of scientific realism and anti-realism.

[25] Mill 1872: 243; Duddington 1919; Ayer 1953.

[26] Comesaña and Klein 2019: § 5.

[27] See e.g. Berkeley 1904 [1710]; Austin 1962; and Lyons 2019 for an overview.

[28] Gordon n.d.

[29] See e.g. Frances and Matheson 2019: § 5.

[30] Fricker 2007; Alcoff 2010.

[31] See e.g. Stanley 2005.

[32] Prichard et al. 2019.

[33] See e.g. Cohen 1986; DeRose 1992.

[34] Butchvarov 1970.

[35] Quine 1969; Kornblith 2002.

[36] For excellent overviews, see Steup 2019; Truncellito 2019; Steup, Turri, and Sosa 2013; BonJour 2002; and Huemer 2002.

[37] Perhaps in order to know whether one has acquired any knowledge, one must know what knowledge is and how we achieve it. This is the basis of Descartes’s 1984 [1641] strategy.

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About the Author

Tom Metcalf is an associate professor at Spring Hill College in Mobile, AL. He received his PhD in philosophy from the University of Colorado, Boulder. He specializes in ethics, metaethics, epistemology, and the philosophy of religion. Tom has two cats whose names are Hesperus and Phosphorus. shc.academia.edu/ThomasMetcalf

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7.2 Knowledge

Learning objectives.

By the end of this section, you will be able to:

• Identify and explain the elements of Plato’s traditional account of knowledge.
• Describe the Gettier problem.
• Recall a Gettier case and explain how it is a counterexample to the traditional account of knowledge.
• Identify and explain a way of thinking that attempts to solve the Gettier problem.

What does it mean to say that one knows something? Knowledge is an important concept in all areas of thought. Knowledge is the goal and therefore enjoys a special status. Investigating the nature of knowledge reveals the importance of other concepts that are key to epistemological theorizing—justification in particular.

Plato and the Traditional Account of Knowledge

Plato , one of the most important of the Greek philosophers, hypothesized that knowledge is justified true belief. Plato’s analysis is known as the traditional account of knowledge . Plato’s definition is that a person S knows proposition P if and only if

• S believes P, and
• S is justified in believing P (Plato 1997b).

Plato’s hypothesis on knowledge, often referred to as the JTB account (because it is “ justified true belief ”), is highly intuitive. To say “John knows P, but he does not believe P” sounds wrong. In order to know something, a subject must first believe it. And one also cannot say “Ali knows P, but P is false.” A person simply cannot have knowledge of false things. Knowledge requires truth. Last, someone should not claim to know P if they have no reason to believe P (a reason to believe being justification for P).

Problems with the Traditional Account of Knowledge

Amazingly, Plato ’s view that knowledge is justified true belief was generally accepted until the 20th century (over 2,000 years!). But once this analysis was questioned, a flurry of developments occurred within epistemology in the latter half of the 20th century. This section discusses the counterexample method at play in the dialectic concerning what knowledge is. Plato’s JTB analysis was the first to come under scrutiny.

In 1963, American philosopher Edmund Gettier (1927–2021) published a short paper titled “Is Justified True Belief Knowledge?,” which upended the JTB canon in Western philosophy. Gettier presents two counterexamples to Plato’s analysis of knowledge. In these counterexamples, a person seems to have a justified true belief, yet they do not seem to have knowledge. While Gettier is credited with the first popular counterexample to the JTB account, he was not the first philosopher to articulate a counterexample that calls into question Plato’s analysis. But because Gettier published the first influential account, any example that seems to undermine Plato’s JTB account of knowledge is called a Gettier case . Gettier cases illustrate the inadequacy of the JTB account—a problem referred to as the Gettier problem .

Dharmakīrti’s Mirage

The earliest known Gettier case, long predating the term, was conceived by the eighth century Indian Buddhist philosopher Dharmakīrti . Dharmakīrti’s case asks one to imagine a weary nomad traveling across the desert in search of water (Dreyfus 1997). The traveler crests a mountain and sees what appears to be an oasis in the valley below, and so comes to believe that there is water in the valley. However, the oasis is just a mirage. Yet there is water in the valley, but it is just beneath the surface of the land where the mirage is. The traveler is justified in believing there is water in the valley due to sensory experience. Furthermore, it is true that there is water in the valley. However, the traveler’s belief does not seem to count as knowledge. Dharmakīrti’s conclusion is that the traveler cannot be said to know there is water in the valley because the traveler’s reason for believing that there is water in the valley is an illusory mirage.

Russell’s Case

Perhaps you’ve heard the phrase “Even a broken clock is right twice a day.” The next case relies on this fact about broken clocks. In 1948, Bertrand Russell offered a case in which a man looks up at a stopped clock at exactly the correct time:

There is the man who looks at a clock which is not going, though he thinks it is, and who happens to look at it at the moment when it is right; this man acquires a true belief as to the time of day, but cannot be said to have knowledge. (Russell 1948, 154)

Imagine that the clock the man looks at is known for its reliability. Hence, the man is justified in believing that the time is, for example, 4:30. And, as the cases supposes, it is true that it is 4:30. However, given that the clock is not working and that the man happens to look up at one of the two times a day that the clock is correct, it is only a matter of luck that his belief happens to be true. Hence, Russell concludes that the man cannot be said to know the correct time.

Fake Barn Country

The last Gettier case we will look at is from American philosopher Carl Ginet (b. 1932) (Goldman 1976). Henry is driving through a bucolic area of farmland and barns. What he doesn’t realize, however, is that the area is currently being used as a movie set, and all the barns save one are actually barn facades. While looking at one of the barns, Henry says to himself, “That is a barn.” Luckily for Henry, the one he points to is the one true barn in the area. Again, all the conditions in Plato’s analysis of knowledge are met. It is true that Henry is looking at a real barn, and he believes it is a barn. Furthermore, he has come to this belief utilizing justifiable means—he is using his vision, in normal lighting, to identify a common object (a barn). Yet one cannot reasonably say that Henry knows the barn is a barn because he could have, by chance, accidentally identified one of the fake barns as a true barn. He fortunately happens to pick the one true barn.

Table 7.2 summarizes the Gettier cases discussed in this chapter.

Fixing Plato’s Traditional Account of Knowledge

Gettier cases demonstrate that Plato ’s traditional account of knowledge as justified true belief is wrong. Specifically, Gettier cases show that a belief being true and justified is not sufficient for that belief to count as knowledge. In all the cases discussed, the subject seems to have a justified true belief but not knowledge. Notice that this does not mean that belief, truth, or justification is not necessary for knowledge. Indeed, when speaking of propositional knowledge, all philosophers grant that belief and truth are necessary conditions for knowledge. A person cannot be said to know a proposition if they do not believe that proposition. And clearly, if a belief is to count as knowledge, then that believe simply cannot be false. Accordingly, attempts to solve the Gettier problem do one of two things: either they replace the justification condition with something more robust, or they add a fourth condition to JTB to make the account sufficient.

No False Premises

In Dharmakīrti’s case, the nomad believes there is water in the valley based on the false belief that a mirage is an oasis. And in Russell’s case, the man bases his true belief about the time on the false belief that the clock he’s looking at is working. In both cases, the inference that leads to the true belief passes through false premises. In response to this fact, American philosopher Gilbert Harman (1928–2021) suggested adding a condition to the JTB account that he termed “no false lemmas” (Harman 1973). A false lemma is a false premise, or step in the reasoning process. Harman’s fourth condition is that a person’s belief cannot be based on an inference that uses false premises. According to Harman, S knows P if and only if (1) P is true, (2) S believes P, (3) S is justified in believing P, and (4) S did not infer P from any falsehoods.

Harman theorized that many counterexamples to the traditional account share a similar feature: the truth of the belief is not appropriately connected to the evidence used to deduce that belief. Going back to Dharmakīrti ’s case, what makes the statement “There’s water in the valley” true is the fact that there is water below the surface. However, the nomad comes to believe that there is water based on the mistaken belief that a mirage is an oasis, so what makes the belief true is not connected to the reason the nomad believes it. If Harman’s condition that the reasoning that leads to belief cannot pass through false steps is added, then the nomad’s belief no longer counts as knowledge.

Harman ’s emendation explains why the nomad does not have knowledge and accounts for the intuition that the man in Russell’s case does not actually know what time it is. However, this cannot take care of all Gettier cases . Consider the case of Henry in fake barn country. Henry comes to believe he is looking at a barn based on his perceptual experience of the barn in front of him. And Henry does look at a real barn. He does not reason through any false premises, such as “All the structures on my drive are barns.” His inference flows directly from his perceptual experience of a real barn. Yet it is a matter of luck that Henry isn’t looking at one of the many barn facades in the area, so his belief still does not seem to count as knowledge. Because Harman’s account is vulnerable to the barn counterexample, it does not solve the Gettier problem.

Ruling Out Defeaters and Alternatives

While driving through fake barn country, Henry happens to form the belief “That is a barn” when looking at the only real barn in the area. While Henry’s belief is not based on false premises, there still seems to be something wrong with it. Why? The problem is that certain facts about Henry’s environment (that it is filled with barn facades), if known, would undermine his confidence in the belief. That the area is predominantly filled with barn facades is what is known as a defeater because it serves to defeat the justification for his belief. Contemporary American philosophers Keith Lehrer and Thomas Paxson Jr. suggest that justified true belief is knowledge as long as there are no existing defeaters of the belief (Lehrer and Paxson 1969). S has knowledge that P if and only if (1) P is true, (2) S believes P, (3) S is justified in believing P, and (4) there exist no defeaters for P. The added fourth condition means that there cannot exist evidence that, if believed by S, would undermine S’s justification.

The “no defeaters” condition solves all three Gettier cases discussed so far because in each case, there exists evidence that, if possessed by the subject, would undermine their justification. Henry cannot be said to know he’s looking at a barn because of the evidence that most of the barns in the area are fake, and Russell’s man doesn’t know the time because the clock is stopped. The “no defeaters” condition thus helps solve many Gettier cases. However, we now need a thorough account of when evidence counts as a defeater . We are told that a defeater is evidence that would undermine a person’s justification but not how it does this. It cannot be that all evidence that weakens a belief is a defeater because this would make knowledge attainment much more difficult. For many of our justified true beliefs , there exists some evidence that we are unaware of that could weaken our justification. For example, we get many beliefs from other people. Research indicates that people tell an average of one lie per day (DePaulo et al. 1996; Serota, Levine, and Boster 2010). So when someone tells you something in conversation, often it is true that the person has lied once today. Is the evidence that a person has lied once today enough evidence to undermine your justification for believing what they tell you?

Notice that because a defeater is evidence that would undermine a person’s justification, what counts as a defeater depends on what justification is. Of the theories of knowledge examined so far, all of them treat justification as basic. They state that a belief must be justified but not how to measure or determine justification.

The Problem with Justification

The traditional analysis of knowledge explains that knowledge is justified true belief. But even if we accept this definition, we could still wonder whether a true belief is knowledge because we may wonder if it is justified. What counts as justification ? Justification is a rather broad concept. Instead of simply stating that justification is necessary for knowledge, perhaps a thorough account of knowledge ought to instead spell out what this means. The next section looks more deeply at how to understand justification and how some theorists suggest replacing the justification condition in order to solve the Gettier problem.

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Plato on Knowledge in the Theaetetus

This article introduces Plato’s dialogue the Theaetetus (section 1), and briefly summarises its plot (section 2). Two leading interpretations of the dialogue, the Unitarian and Revisionist readings, are contrasted in section 3. Sections 4 to 8 explain and discuss the main arguments of the chief divisions of the dialogue. Section 9 provides some afterthoughts about the dialogue as a whole.

1. Introduction

2. summary of the dialogue, 3. overall interpretations of the theaetetus, 4. the introduction to the dialogue: 142a–145e, 5. definition by examples: 146a–151d, 6.1 the definition of knowledge as perception: 151d–e, 6.2 the “cold wind” argument; and the theory of flux: 152a–160e, 6.3 the refutation of the thesis that knowledge is perception: 160e5–186e12, 6.4 the digression: 172c1–177b7, 6.5 last objection to protagoras: 177c6–179b5, 6.6 last objection to heracleitus: 179c1–183c2, 6.7 the final refutation of d1 : 183c4–187a8, 7.1 the puzzle of misidentification: 187e5–188c8, 7.2 second puzzle about false belief: “believing what is not”: 188c10–189b9, 7.3 third puzzle about false belief: allodoxia : 189b10–190e4, 7.4 fourth puzzle about false belief: the wax tablet: 190e5–196c5, 7.5 fifth puzzle about false belief: the aviary: 196d1–200d4, 7.6 the final refutation of d2 : 200d5–201c7, 8.1 the dream of socrates: 201d8–202d7, 8.2 critique of the dream theory: 202d8–206c2, 8.3 three attempts to understand logos : 206c2–210a9, 9. conclusion, other internet resources, related entries.

The Theaetetus, which probably dates from about 369 BC, is arguably Plato’s greatest work on epistemology. (Arguably, it is his greatest work on anything.) Plato (c.427–347 BC) has much to say about the nature of knowledge elsewhere. But only the Theaetetus offers a set-piece discussion of the question “What is knowledge?”

Like many other Platonic dialogues, the Theaetetus is dominated by question-and-answer exchanges, with Socrates as main questioner. His two respondents are Theaetetus, a brilliant young mathematician, and Theaetetus’ tutor Theodorus, who is rather less young (and rather less brilliant).

Also like other Platonic dialogues, the main discussion of the Theaetetus is set within a framing conversation (142a–143c) between Eucleides and Terpsion (cp. Phaedo 59c). This frame may be meant as a dedication of the work to the memory of the man Theaetetus. Sedley 2004 (6–8) has argued that it is meant to set some distance between Plato’s authorial voice and the various other voices (including Socrates’) that are heard in the dialogue. Alternatively, or also, it may be intended, like Symposium 172–3, to prompt questions about the reliability of knowledge based on testimony. (Cp. the law-court passage ( Theaetetus 201a–c), and Socrates’ dream ( Theaetetus 201c–202c).)

The Theaetetus ’ most important similarity to other Platonic dialogues is that it is aporetic —it is a dialogue that ends in an impasse . The Theaetetus reviews three definitions of knowledge in turn; plus, in a preliminary discussion, one would-be definition which, it is said, does not really count. Each of these proposals is rejected, and no alternative is explicitly offered. Thus we complete the dialogue without discovering what knowledge is. We discover only three things that knowledge is not ( Theaetetus 210c; cp. 183a5, 187a1).

This matters, given the place that the Theaetetus is normally assigned in the chronology of Plato’s writings. Most scholars agree that Plato’s first writings were the “Socratic” dialogues (as they are often called), which ask questions of the “What is…?” form and typically fail to find answers: “What is courage?” ( Laches ), “What is self-control?” ( Charmides ), “What is justice?” ( Alcibiades I ; Republic 1), “What is holiness?” ( Euthyphro ), “What is friendship?” ( Lysis ), “What is virtue?” ( Meno ), “What is nobility?” ( Hippias Major ). After some transitional works ( Protagoras, Gorgias, Cratylus, Euthydemus ) comes a series of dialogues in which Plato writes to a less tightly-defined format, not always focusing on a “What is…?” question, nor using the question-and-answer interrogative method that he himself depicts as strictly Socratic: the Phaedo , the Phaedrus , the Symposium, and the Republic . In these dialogues Plato shows a much greater willingness to put positive and ambitious metaphysical views in Socrates’ mouth, and to make Socrates the spokesman for what we call “Plato’s theory of Forms.”

After these, it is normally supposed that Plato’s next two works were the Parmenides and the Theaetetus , probably in that order. If so, and if we take as seriously as Plato seems to the important criticisms of the theory of Forms that are made in the Parmenides , then the significance of the Theaetetus ’s return to the aporetic method looks obvious. Apparently Plato has abandoned the certainties of his middle-period works, such as the theory of Forms, and returned to the almost-sceptical manner of the early dialogues. In the Theaetetus , the Forms that so dominated the Republic ’s discussions of epistemology are hardly mentioned at all. A good understanding of the dialogue must make sense of this fact.

At the gates of the city of Megara in 369 BC, Eucleides and Terpsion hear a slave read out Eucleides’ memoir of a philosophical discussion that took place in 399 BC, shortly before Socrates’ trial and execution (142a–143c). In this, the young Theaetetus is introduced to Socrates by his mathematics tutor, Theodorus. Socrates questions Theaetetus about the nature of expertise, and this leads him to pose the key question of the dialogue: “What is knowledge?” (143d–145e). Theaetetus’ first response ( D0 ) is to give examples of knowledge such as geometry, astronomy, harmony, arithmetic (146a–c). Socrates objects that, for any x , examples of x are neither necessary nor sufficient for a definition of x (146d–147e). Theaetetus admits this, and contrasts the ease with which he and his classmates define mathematical terms with his inability to define knowledge (147c–148e). Socrates offers to explain Theaetetus’ bewilderment about the question “What is knowledge?” by comparing himself with a midwife: Theaetetus, he suggests, is in discomfort because he is in intellectual labour (148e–151d).

Thus prompted, Theaetetus states his first acceptable definition, which is the proposal that

Socrates does not respond to this directly. Instead he claims that D1 entails two other theories (Protagoras’ and Heracleitus’), which he expounds (151e–160e) and then criticises (160e–183c). Socrates eventually presents no fewer than eleven arguments, not all of which seem seriously intended, against the Protagorean and Heracleitean views. If any of these arguments hit its target, then by modus tollens D1 is also false. A more direct argument against D1 is eventually given at 184–7.

In 187b4–8, Theaetetus proposes a second definition of knowledge:

D2 provokes Socrates to ask: how can there be any such thing as false belief? There follows a five-phase discussion which attempts to come up with an account of false belief. All five of these attempts fail, and that appears to be the end of the topic of false belief. Finally, at 200d–201c, Socrates returns to D2 itself. He dismisses D2 just by arguing that accidental true beliefs cannot be called knowledge , giving Athenian jurymen as an example of accidental true belief.

Theaetetus tries a third time. His final proposal is:

The ensuing discussion attempts to spell out what it might be like for D3 to be true, then makes three attempts to spell out what a logos is.

In 201d–202d, the famous passage known as The Dream of Socrates , a two-part ontology of elements and complexes is proposed. Parallel to this ontology runs a theory of explanation that claims that to explain, to offer a logos, is to analyse complexes into their elements, i.e., those parts which cannot be further analysed. Crucially, the Dream Theory says that knowledge of O is true belief about O plus an account of O ’s composition. If O is not composite, O cannot be known, but only “perceived” (202b6). When Socrates argues against the Dream Theory (202d8–206b11), it is this entailment that he focuses on.

Socrates then turns to consider, and reject, three attempts to spell out what a logos is—to give an account of “account.” The first attempt takes logos just to mean “speech” or “statement” (206c–e). The second account (206e4–208b12) of “ logos of O ” takes it as “enumeration of the elements of O .” The third and last proposal (208c1–210a9) is that to give the logos of O is to cite the sêmeion or diaphora of O , the “sign” or diagnostic feature wherein O differs from everything else.

All three attempts to give an account of “account” fail. The day’s discussion, and the dialogue, end in aporia. Socrates leaves to face his enemies in the courtroom.

The Theaetetus is a principal field of battle for one of the main disputes between Plato’s interpreters. This is the dispute between Unitarians and Revisionists .

Unitarians argue that Plato’s works display a unity of doctrine and a continuity of purpose throughout. Unitarians include Aristotle, Proclus, and all the ancient and mediaeval commentators; Bishop Berkeley; and in the modern era, Schleiermacher, Ast, Shorey, Diès, Ross, Cornford, and Cherniss.

Revisionists retort that Plato’s works are full of revisions, retractations, and changes of direction. Eminent Revisionists include Lutoslawski, Ryle, Robinson, Runciman, Owen, McDowell, Bostock, and many recent commentators.

Unitarianism is historically the dominant interpretive tradition. Revisionism, it appears, was not invented until the text-critical methods, such as stylometry, that were developed in early nineteenth-century German biblical studies were transferred to Plato.

In the twentieth century, a different brand of Revisionism has dominated English-speaking Platonic studies. This owes its impetus to a desire to read Plato as charitably as possible, and a belief that a charitable reading of Plato’s works will minimise their dependence on the theory of Forms. (Corollary: Unitarians are likelier than Revisionists to be sympathetic to the theory of Forms.)

Unitarianism could be the thesis that all of Plato’s work is, really, Socratic in method and inspiration, and that Plato should be credited with no view that is not endorsed in the early dialogues. (In some recent writers, Unitarianism is this thesis: see Penner and Rowe (2005).) But this is not the most usual form of Unitarianism, which is more likely to “read back” the concerns of the Phaedo and the Republic into the Socratic dialogues, than to “read forward” the studied agnosticism of the early works into these more ambitious later dialogues. Likewise, Revisionism could be evidenced by the obvious changes of outlook that occur, e.g., between the Charmides and the Phaedo , or again between the Protagoras and the Gorgias . But the main focus of the Revisionist/Unitarian debate has never been on these dialogues. The contrasts between the Charmides and the Phaedo , and the Protagoras and the Gorgias, tell us little about the question whether Plato ever abandoned the theory of Forms. And that has usually been the key dispute between Revisionists and Unitarians.

Hence the debate has typically focused on the contrast between the “the Middle Period dialogues” and “the Late dialogues.” Revisionists say that the Middle Period dialogues enounce positive doctrines, above all the theory of Forms, which the Late dialogues criticise, reject, or simply bypass. The main place where Revisionists (e.g., Ryle 1939) suppose that Plato criticises the theory of Forms is in the Parmenides (though some Revisionists find criticism of the theory of Forms in the Theaetetus and Sophist as well). The main places where Revisionists look to see Plato managing without the theory of Forms are the Theaetetus and Sophist .

Ryle’s Revisionism was soon supported by other Oxford Plato scholars such as Robinson 1950 and Runciman 1962 (28). Revisionism was also defended by G.E.L. Owen. More recently, McDowell 1976, Bostock 1988, and Burnyeat 1990 are three classic books on the Theaetetus of a decidedly Revisionist tendency. (McDowell shows a particularly marked reluctance to bring in the theory of Forms anywhere where he is not absolutely compelled to.)

Revisionists are committed by their overall stance to a number of more particular views . They are more or less bound to say that the late Plato takes the Parmenides’ critique of the theory of Forms to be cogent, or at least impressive; that the Sophist’ s theory of “the five greatest kinds” ( Sophist 254b–258e) is not a development of the theory of Forms; and that the Timaeus was written before the Parmenides, because of the Timaeus’ apparent defence of theses from the theory of Forms. Their line on the Theaetetus will be that its argument does not support the theory of Forms; that the Theaetetus is interesting precisely because it shows us how good at epistemology Plato is once he frees himself from his obsession with the Forms.

Some of these Revisionist claims look easier for Unitarians to dispute than others. For example, Plato does not think that the arguments of Parmenides 130b–135c actually disprove the theory of Forms. Rather, it is obviously Plato’s view that Parmenides’ arguments against the Forms can be refuted. See Parmenides 135a–d, where Plato explicitly says—using Parmenides as his mouthpiece—that these arguments will be refuted by anyone of adequate philosophical training. (Whether anyone “of adequate philosophical training” is available is, of course, another question.)

Another problem for the Revisionist concerns Owen 1965’s proposal, adopted by Bostock 1988, to redate the Timaeus to the Middle Period, thus escaping the conclusion that Plato still accepted the theory of Forms at the end of his philosophical career. The trouble with this is that it is not only the Timaeus that the Revisionist needs to redate. In quite a number of apparently Late dialogues, Plato seems sympathetic to the theory of Forms: see e.g., Philebus 61e and Laws 965c.

On the other hand, the Revisionist claim that the Theaetetus shows Plato doing more or less completely without the theory of Forms is very plausible. There are no explicit mentions of the Forms at all in the Theaetetus , except possibly (and even this much is disputed) in what many take to be the philosophical backwater of the Digression. The main argument of the dialogue seems to get along without even implicit appeal to the theory of Forms. In the Theaetetus , Revisionism seems to be on its strongest ground of all.

The usual Unitarian answer is that this silence is studied. In the Theaetetus, Unitarians suggest, Plato is showing what knowledge is not . His argument is designed to show that certain sorts of alternatives to Plato’s own account of knowledge must fail. Plato demonstrates this failure by the ‘maieutic’ method of developing those accounts until they fail. Thus the Theaetetus shows the impossibility of a successful account of knowledge that does not invoke the Forms.

The fault-line between Unitarians and Revisionists is the deepest fissure separating interpreters of the Theaetetus . It is not the only distinction among overall interpretations of the dialogue. It has also been suggested, both in the ancient and the modern eras, that the Theaetetus is a sceptical work; that the Theaetetus is a genuinely aporetic work; and that the Theaetetus is a disjointed work. However, there is no space to review these possibilities here. It is time to look more closely at the detail of the arguments that Plato gives in the distinct sections of the dialogue.

We should not miss the three philosophical theses that are explicitly advanced in the Introduction. They are offered without argument by Socrates, and agreed to without argument by Theaetetus, at 145d7–145e5:

• The wise are wise sophiai (= by/ because of/ in respect of/ as a result of wisdom:145d11).
• To learn is to become wiser about the topic you are learning about (145d8–9).
• Wisdom ( sophia ) and knowledge ( epistêmê ) are the same thing (145e5).

All three theses might seem contentious today. (1) seems to allude to Phaedo 100e’s notorious thesis about the role of the Form of F -ness in any x ’s being F —that x is F “ by the Form of F -ness.” (2) looks contentious because it implies (3); and (3) brings me to a second question about 142a–145e (which is also an important question about the whole dialogue): What is the meaning of the Greek word that I am translating as “knowledge,” epistêmê ?

Much has been written about Plato’s words for knowledge. One important question raised by Runciman 1962 is the question whether Plato was aware of the commonplace modern distinction between knowing that, knowing how, and knowing what (or whom). Nothing is more natural for modern philosophers than to contrast knowledge of objects (knowledge by acquaintance or objectual knowledge; French connaître ) with knowledge of how to do things (technique knowledge), and with knowledge of propositions or facts (propositional knowledge; French savoir ). Runciman doubts that Plato is aware of this threefold distinction (1962, 17): “At the time of writing the Theaetetus Plato had made no clear distinction [between] knowing that, knowing how, and knowing by acquaintance.”

Against this, Plato’s word for knowing how is surely tekhnê , from which we get the English word “technique.” Plato obviously thinks tekhnê incidental to a serious discussion of epistêmê . This is part of the point of the argument against definition by examples that begins at 146d (cp. 177c–179b).

As for the difference between knowing that and knowledge by acquaintance: the Theaetetus does mix passages that discuss the one sort of knowledge with passages that discuss the other. This does not imply that Plato was unaware of the difference. Perhaps he wants to discuss theories of knowledge that find deep conceptual connections between the two sorts of knowledge.

A grammatical point is relevant here. The objectual “I know Socrates” in classical Greek is oida (or gignôskô ) ton Sôkratên ; the propositional “I know Socrates is wise” is oida (or gignôskô ) ton Sôkratên sophon onta , literally “I know Socrates being wise” or, colloquially, just oida ton Sôkratên sophon , literally “I know Socrates wise”. Thus the Greek idiom can readily treat the object of propositional knowledge, which in English would most naturally be a that-clause, as a thing considered as having a quality . We might almost say that Greek treats what is known in propositional knowledge as just one special case of what is known in objectual knowledge. This suggests that the ancient Greeks naturally saw propositional and objectual knowledge as more closely related than we do (though not necessarily as indistinguishable). If so, Plato may have felt able to offer a single treatment for the two kinds of knowledge without thereby confusing them. The point will be relevant to the whole of the Theaetetus .

At 145d Socrates states the “one little question that puzzles” him: “What is knowledge?” Theaetetus’ first response ( D0 ) is to offer examples of knowledge (146c). Socrates rejects this response, arguing that, for any x , examples of x are neither necessary nor sufficient for a definition of x . They are not necessary, because they are irrelevant (146e). They are not sufficient, because they presuppose the understanding that a definition is meant to provide (147a–b). Moreover (147c), a definition could be briefly stated, whereas talking about examples is “an interminable diversion” ( aperanton hodon ).

Does Socrates produce good arguments against definition by examples? Many philosophers think not (McDowell 1976 (115), Geach 1966, Santas 1972, Burnyeat 1977). They often argue this by appealing to the authority of Wittgenstein, who famously complains ( The Blue and Brown Books , 20) that “When Socrates asks the question, ‘What is knowledge?’, he does not regard it even as a preliminary answer to enumerate cases of knowledge.” For arguments against this modern consensus, see Chappell 2005 (36–37).

Some commentators have taken Socrates’ critique of definition by examples to be an implicit critique of the Republic ’s procedure of distinguishing knowledge, belief, and ignorance by distinguishing their objects. The suggestion was first made by Ryle 1990 (23), who points out that “Socrates makes it clear that what he wants discussed is not a list of things that people know,” “but an elucidation of the concept of knowledge.” Ryle suggests that “Attention to this simple point might have saved Cornford from saying that the implicit conclusion of the dialogue is that ‘true knowledge has for its objects things of a different order’.” Ryle thinks it “silly” to suggest that knowledge can be defined merely by specifying its objects.

However, 145e–147c cannot be read as a critique of the Republic ’s procedure of distinguishing knowledge from belief by their objects. 145e–147c is not against defining knowledge by examples of objects of knowledge; it is against defining knowledge by examples of kinds of knowledge. (See e.g., 146e7, “We weren’t wanting to make a list of kinds of knowledge.”) This is a different matter.

Why, anyway, would the Platonist of the Republic think that examples of the objects of knowledge are enough for a definition of knowledge? He is surely the last person to think that. The person who will think this is the empiricist, who thinks that we acquire all our concepts by exposure to examples of their application: Locke, Essay II.1, Aristotle, Posterior Analytics 100a4–9. For the Platonist, definition by examples is never even possible; for the empiricist, definition by examples is the natural method in every case. This suggests that empiricism is a principal target of the argument of the Theaetetus . More about this in sections 6–8.

Theaetetus is puzzled by his own inability to answer Socrates’ request for a definition of knowledge, and contrasts it with the ease with which he can provide mathematical definitions. He gives an example of a mathematical definition; scholars are divided about the aptness of the parallel between this, and what would be needed for a definition of knowledge. Socrates’ response, when Theaetetus still protests his inability to define knowledge, is to compare himself to a midwife in a long and intricate analogy.

Many ancient Platonists read the midwife analogy, and more recently Cornford 1935 has read it, as alluding to the theory of recollection. But it is better not to import metaphysical assumptions into the text without good reason, and it is hard to see what the reason would be beyond a determination to insist that Plato always maintained the theory of recollection. With or without this speculation, the midwife passage does tell us something important about how the Theaetetus is going to proceed. In line with the classification that the ancient editors set at the front of the dialogue, it is going to be peirastikos , an experimental dialogue. It will try out a number of suggestions about the nature of knowledge. As in the aporetic dialogues, there is no guarantee that any of these suggestions will be successful (and every chance that none of them will be).

So read, the midwife passage can also tell us something important about the limitations of the Theaetetus’ inquiry. The limitations of the inquiry are the limitations of the main inquirers, and neither (the historical) Socrates nor Theaetetus was a card-carrying adherent of Plato’s theory of Forms. Perhaps the dialogue brings us only as far as the threshold of the theory of Forms precisely because, on Socratic principles, one can get no further. To get beyond where the Theaetetus leaves off, you have to be a Platonist. (For book-length developments of this reading of the Theaetetus, see Sedley 2004 and Chappell 2005.)

6. First Definition ( D1 ): “Knowledge is Perception”: 151e–187a

Between Stephanus pages 151 and 187, and leaving aside the Digression, 172–177 (section 6d), 31 pages of close and complex argument state, discuss, and eventually refute the first of Theaetetus’ three serious attempts at a definition of knowledge:

As before, there are two main alternative readings of 151–187: the Unitarian and the Revisionist. On the Unitarian reading, Plato’s purpose is to salvage as much as possible of the theories of Protagoras and Heracleitus (each respectfully described as ou phaulon : 151e8, 152d2). Plato’s strategy is to show that these theories have their own distinctive area of application, the perceptible or sensible world, within which they are true. However, the sensible world is not the whole world, and so these theories are not the whole truth. We get absurdities if we try to take them as unrestrictedly true. To avoid these absurdities it is necessary to posit the intelligible world (the world of the Forms) alongside the sensible world (the world of perception). When this is done, Platonism subsumes the theories of Protagoras and Heracleitus as partial truths. On this reading, the strategy of the discussion of D1 is to transcend Protagoras and Heracleitus: to explain their views by showing how they are, not the truth, but parts of a larger truth. In the process the discussion reveals logical pressures that may push us towards the two-worlds Platonism that many readers, e.g., Ross and Cornford, find in the Republic and Timaeus.

On the Revisionist reading, Plato’s purpose is to refute the theories of Protagoras and Heracleitus. He thinks that the absurdities those theories give rise to, come not from trying to take the theories as unrestrictedly true, but from trying to take them as true at all , even of the sensible world. Anyone who tries to take seriously the thesis that knowledge is perception has to adopt theories of knowledge and perception like Protagoras’ and Heracleitus’. But their theories are untenable. By modus tollens this shows that D1 itself is untenable. On this reading, the strategy of the discussion of D1 is to move us towards the view that sensible phenomena have to fall under the same general metaphysical theory as intelligible phenomena.

This outline of the two main alternatives for 151–187 shows how strategic and tactical issues of Plato interpretation interlock. For instance, the outline shows how important it is for an overall understanding of the Theaetetus to have a view on the following questions of detail (more about them later):

• At 156a–157c, is Socrates just reporting, or also endorsing, a Heracleitean flux theory of perception?
• What is the date of the Timaeus , which seems (28–29, 45b–46c, 49e) to present a very similar theory of perception to that found in Theaetetus 156–7?
• What does Plato take to be the logical relations between the three positions under discussion in 151–184 ( D1 , Protagoras’ theory, and Heracleitus’ theory)? The closer he takes them to be, the more support that seems to give to the Revisionist view that the whole of 151–187 is one gigantic modus tollens . The more separate they are, the better for those versions of Unitarianism that suggest that Plato wants to pick and choose among the positions offered in 151–187.

So much for the overall structure of 151–187; now for the parts.

At 151d7–e3 Theaetetus proposes:

Socrates immediately equates D1 with Protagoras’s thesis that

and takes this, in turn, to entail the thesis:

Socrates then adds that, in its turn, PS entails Heracleitus’ view that “All is flux,” that there are no stably existing objects with stably enduring qualities .

The first of these deft exchanges struck the Anonymous Commentator as disingenuous: “Plato himself knew that Protagoras’ opinion about knowledge was not the same as Theaetetus’” (Anon, ad loc. ). Certainly it is easy to see counter-examples to the alleged entailment. Take, for instance, the thesis that knowledge is awareness (which is often the right way to translate aisthêsis ). Or take the thesis that to know is to perceive things as God, or the Ideal Observer, perceives them, and that we fail to know (or to perceive) just insofar as our opinions are other than God’s or the Ideal Observer’s. These theses are both versions of D1 . Neither version entails the claim that “man is the measure of all things” ( Hm )—nor the Protagorean view that lies behind that slogan.

So how, if at all, does D1 entail all the things that Socrates apparently makes it entail in 151–184? And does Plato think it has all these entailments? Evidently the answer to that depends on how we understand D1 . In particular, it depends on the meaning of the word aisthêsis , “perception,” in D1 . If the slogan “Knowledge is perception” equates knowledge with what ordinary speakers of classical Greek would have meant by aisthêsis , then D1 does not entail Protagoras’ and Heracleitus’ views. In the ordinary sense of aisthêsis , there are (as just pointed out) too many other possible ways of spelling out D1 for the move from D1 to Hm to be logically obligatory. But if the slogan “Knowledge is perception” equates knowledge with what Protagoras and Heracleitus meant by aisthêsis , D1 does entail Protagoras’ and Heracleitus’ views. Of course it does; for then D1 simply says that knowledge is just what Protagoras and Heracleitus say knowledge is.

At 152b1–152c8 Socrates begins his presentation of Protagoras’ view that things are to any human just as they appear to that human by taking the example of a wind which affects two people differently. Such cases, he says, support Protagoras’ analysis: “that the wind is cold to the one who feels cold , but not cold to the one who does not feel cold. ”

Some scholars (Cornford 1935, 33–4; Waterlow 1977) think that the point of the argument is that both “the wind in itself is cold” and “the wind in itself is not cold (but warm)” are true: “‘Warm’ and ‘cold’ are two properties which can co-exist in the same physical object. I perceive the one, you perceive the other.” The trouble with this suggestion is that much of the detail of the Protagorean/Heracleitean position in 151–184 seems to be generated by Protagoras’ desire to avoid contradiction. If Cornford thinks that Protagoras is not concerned to avoid contradicting himself, then he has a huge task of reinterpretation ahead of him.

Rather, perhaps, the point of the argument is this: Neither “The wind in itself is cold” nor “The wind in itself is warm” is true. If we had grounds for affirming either, we would have equally good grounds for affirming both; but the conjunction “The wind in itself is cold and the wind in itself is warm” is a contradiction. This contradiction, says Protagoras, obliges us to give up all talk about “the wind in itself,” and switch to relativised talk about the wind as it seems to me or to you, etc. (The same contradiction pushes the Plato of the Republic in the opposite direction: it leads him to place no further trust in any relativised talk, precisely because such talk cannot get us beyond such contradictions.)

So we have moved from D1 , to Hm , to PS . At 152c8–152e1 Socrates adds that, in its turn, PS entails Heracleitus’ view that “All is flux,” that there are no stably existing objects with stably enduring qualities. The reason given for this is the same thought as the one at the centre of the cold-wind argument: that everything to which any predicate can be applied, according to one perception, can also have the negation of that predicate applied to it, according to an opposite perception with equally good credentials.

After a passage (152e1–153d5) in which Socrates presents what seem to be deliberately bad arguments, eight of them, for Heracleitus’ flux thesis, Socrates notes three shocking theses which the flux theory implies:

• Qualities have no independent existence in time and space (153d6–e1).
• Qualities do not exist except in perceptions of them (153e3–154a8).
• (The dice paradox:) changes in a thing’s qualities are not so much changes in that thing as in perceptions of that thing (154a9–155c6).

These shocking implications, Socrates says, give the phenomenal subjectivist his reason to reject the entire object/quality metaphysics, and to replace it with a metaphysics of flux.

In 155c–157c the flux theory is used to develop a Protagorean/Heracleitean account of perception, to replace accounts based on the object/property ontology of common sense. Socrates notes the subversive implications of the theory of flux for the meaningfulness and truth-aptness of most of our language as it stands. (He returns to this point at 183a–b.) The ontology of the flux theory distinguishes kinds of “process” ( kinêsis ), i.e., of flux, in two ways: as fast or slow, and as active or passive. Hence there are four such processes. On these the flux theory’s account of perception rests.

A rather similar theory of perception is given by Plato in Timaeus 45b–46c, 67c–68d. This fact has much exercised scholars, since it relates closely to the question whether Plato himself accepts the flux theory of perception (cp. Theaetetus 157c5). The question is important because it connects with the question of whether the Revisionist or Unitarian reading of 151–187 is right. (For more on this issue, see Cornford 1935 (49–50); Crombie 1963, II (21–22); Burnyeat 1990 (17–18); McDowell 1973 (139–140), Chappell 2005 (74–78).)

At 157c–160c Socrates states a first objection to the flux theory. This asks how the flux theorist is to distinguish false (deceptive) appearances such as dreams from the true (undeceptive) appearances of the waking world. The flux theorist’s answer is that such appearances should not be described as ‘true’ and ‘false’ appearances to the same person. Rather they should be described as different appearances to different people. According to the flux theorist, we have the same person if and only if we have the same combination of a perception and a perceiving (159c–d). So there is no need to call any appearances false . Thus we preserve the claim that all appearances are true—a claim which must be true if knowledge is perception in the sense that Socrates has taken that definition.

160b–d summarises the whole of 151–160. Socrates shows how the exploration of Theaetetus’ identification of knowledge with perception has led us to develop a whole battery of views: in particular, a Protagorean doctrine of the incorrigibility of perception, and a Heracleitean account of what perception is. Thus “perception has one of the two marks of knowledge, infallibility” (Cornford 1935, 58); “and, if we can accept Protagoras’ identification of what appears to me with what is, ignoring the addition ‘for me’ and the distinction between being and becoming, the case will be complete.”

160e marks the transition from the statement and exposition of the definition of knowledge as perception ( D1 ), to the presentation of criticism and refutation of that definition.

Scholars have divided about the overall purpose of 160e–186e. Mostly they have divided along the lines described in section 3, taking either a Revisionist or a Unitarian view of Part One of the Theaetetus .

Revisionists say that the target of the critique of 160e–186e is everything that has been said in support and development of D1 ever since 151. Unitarians argue that Plato’s criticism of D1 in 160e–186e is more selective. Obviously his aim is to refute D1 , the equation of knowledge with perception. But that does not oblige him to reject the account of perception that has been offered in support of D1 . And Plato does not reject this account: he accepts it.

Thus the Unitarian Cornford argues that Plato is not rejecting the Heracleitean flux theory of perception. He is rejecting only D1 ’s claim that knowledge is that sort of perception. It remains possible that perception is just as Heracleitus describes it. Likewise, Cornford suggests, the Protagorean doctrine that “man is the measure of all things” is true provided it is taken to mean only “all things that we perceive .”

If some form of Unitarianism is correct, an examination of 160–186 should show that Plato’s strategy in the critique of D1 highlights two distinctions:

• A distinction between the claim that the objects of perception are in flux, and the claim that everything is in flux.
• A distinction between bare sensory awareness, and judgement on the basis of such awareness.

One vital passage for distinction (1) is 181b–183b. If Unitarianism is right, this passage should be an attack on the Heracleitean thesis that everything is in flux, but not an attack on the Heracleitean thesis that the objects of perception are in flux. According to Unitarians, the thesis that the objects of perception are in flux is a Platonic thesis too. Readers should ask themselves whether this is the right way to read 181b –183b.

Distinction (2) seems to be explicitly stated at 179c. There also seems to be clear evidence of distinction (2) in the final argument against D1 , at 184–187. Distinction (2) is also at work, apparently, in the discussion of some of the nine objections addressed to the Protagorean theory. Some of these objections can plausibly be read as points about the unattractive consequences of failing to distinguish the Protagorean claim that bare sense-awareness is incorrigible (as the Unitarian Plato agrees) from the further Protagorean claim that judgements about sense-awareness are incorrigible (which the Unitarian Plato denies).

The criticism of D1 breaks down into twelve separate arguments, interrupted by the Digression (172c–177c: translated and discussed separately in section 6.4 below). There is no space here to comment in detail on every one of these arguments, some of which, as noted above, have often been thought frivolous or comically intended (cp. 152e1–153d5). Some brief notes on the earlier objections will show what the serious point of each might be.

The first objection to Protagoras (160e–161d) observes that if all perceptions are true, then there is no reason to think that animal perceptions are inferior to human ones: a situation which Socrates finds absurd.

If this objection is really concerned with perceptions strictly so called, then it obviously fails. Protagoras just accepts this supposedly absurd consequence; and apparently he is right to do so. If we consider animals and humans just as perceivers, there is no automatic reason to prefer human perceptions. Many animal perceptions are superior to human perceptions (dogs’ hearing, hawks’ eyesight, dolphins’ echolocatory ability, most mammals’ sense of smell, etc.), and the Greeks knew it, cf. Homer’s commonplace remarks about “far-sighted eagles”, or indeed Aristotle, in the Eudemian Ethics , 1231a5–6. The objection works much better rephrased as an objection about judgements about perceptions, rather than about perceptions strictly so called. Humans are no more and no less perceivers than pigs, baboons, or tadpoles. But they are different in their powers of judgement about perceptions.

This distinction between arguments against a Protagorean view about perception and a Protagorean view about judgement about perception is relevant to the second objection too (161d–162a). This objection (cp. Cratylus 386c) makes the point that Protagoras’ theory implies that no one is wiser than anyone else. Notably, the argument does not attack the idea that perception is infallible. Rather, it attacks the idea that the opinion or judgement that anyone forms on the basis of perception is infallible (161d3). (This is an important piece of support for Unitarianism: cp. distinction (2) above.)

A third objection to Protagoras’ thesis is very quickly stated in Socrates’ two rhetorical questions at 162c2–6. Since Protagoras’ thesis implies that all perceptions are true, it not only has the allegedly absurd consequence that animals’ perceptions are not inferior to humans. It also has the consequence that humans’ perceptions are not inferior to the gods’. This consequence too is now said to be absurd.

As with the first two objections, so here. If we consider divinities and humans just as perceivers, there is no automatic reason to prefer divine perceptions, and hence no absurdity. Plato may well want us to infer that the Greek gods are not different just in respect of being perceivers from humans. But they are different in their powers of judgement about perceptions.

The next four arguments (163a–168c) present counter-examples to the alleged equivalence of knowledge and perception. The fourth observes that, if perception = knowledge, then anyone who perceives an utterance in a given language should have knowledge of that utterance, i.e., understand it—which plainly doesn’t happen. The fifth raises a similar problem about memory and perception: remembering things is knowing them, but not perceiving them. The sixth (the “covered eye”) objection contrasts not perceiving an object (in one sensory modality) with not knowing it . If perception = knowledge, seeing an object with one eye and not seeing it with the other would appear to be a case of the contradictory state of both knowing it and not knowing it. The seventh points out that one can perceive dimly or faintly, clearly or unclearly, but that these adverbial distinctions do not apply to ways of knowing—as they must if knowing is perceiving.

In 165e4–168c5, Socrates sketches Protagoras’s response to these seven objections. Protagoras makes two main points. First, he can meet some of the objections by distinguishing types and occasions of perception. Second, teaching as he understands it is not a matter of getting the pupil to have true rather than false beliefs. Since there are no false beliefs, the change that a teacher can effect is not a change from false belief to true belief or knowledge. Rather, Protagoras’ model of teaching is a therapeutic model. What a good teacher does, according to him, is use arguments (or discourses: logoi ) as a good doctor uses drugs, to replace the state of the soul in which “bad things are and appear” with one in which “good things are and appear.” While all beliefs are true , not all beliefs are beneficial .

A difficulty for Protagoras’ position here is that, if all beliefs are true, then all beliefs about which beliefs are beneficial must be true. But surely, some beliefs about which beliefs are beneficial contradict other beliefs about which beliefs are beneficial; especially if some people are better than others at bringing about beneficial beliefs. (For example, no doubt Plato’s and Protagoras’ beliefs conflict at this point.) This means that Protagoras’ view entails a contradiction of the same sort as the next objection–the famous peritropê —seems to be meant to bring out.

The peritropê (“table-turning”) objection (171a–b) is this. Suppose I believe, as Protagoras does, that “All beliefs are true,” but also admit that “There is a belief that ‘Not all beliefs are true’.” If all beliefs are true, the belief that “Not all beliefs are true” must be true too. But if that belief is true, then by disquotation, not all beliefs are true. So I refute myself by contradicting myself; and the same holds for Protagoras.

The validity of the objection has been much disputed. Burnyeat, Denyer and Sedley all offer reconstructions of the objection that make it come out valid. McDowell and Bostock suggest that although the objection does not prove what it is meant to prove (self-contradiction), it does prove a different point (about self-defeat) which is equally worth making.

Socrates’ ninth objection presents Protagoras’ theory with a dilemma. If the theory is completely general in its application, then it must say that not only what counts as justice in cities, but also what benefits cities, is a relative matter. As Protagoras has already admitted (167a3), it is implausible to say that benefit is a relative notion. But the alternative, which Protagoras apparently prefers, is a conceptual divorce between the notions of justice and benefit, which restrict the application of Protagoras’ theory to the notion of justice. Socrates obviously finds this conceptual divorce unattractive, though he does not, directly, say why. Instead, he offers us the Digression.

An obvious question: what is the Digression for? One answer (defended in Chappell 2004, ad loc.) would be that it is a critique of the society that produces the conceptual divorce between justice and benefit that has just emerged. Socrates draws an extended parallel between two types of character, the philosophical man and the man of rhetoric, to show that it is better to be the philosophical type.

The Digression is “philosophically quite pointless,” according to Ryle 1966: 158. Less dismissively, McDowell 1976: 174 suggests that the Digression serves “a purpose which, in a modern book, might be served by footnotes or an appendix.” Similarly, Cornford 1935 (83) suggests that Plato aims to give the reader some references for anti-relativist arguments that he presents elsewhere: “To argue explicitly against it would perhaps take him too far from the original topic of perception. Instead, he inserts [the Digression], which contains allusions to such arguments in other works of his.”

Perhaps the Digression paints a picture of what it is like to live in accordance with the two different accounts of knowledge, the Protagorean and the Platonist, that Plato is comparing. Thus the Digression shows us what is ethically at stake in the often abstruse debates found elsewhere in the Theaetetus . Its point is that we can’t make a decision about what account of knowledge to accept without making all sorts of other decisions, not only about the technical, logical and metaphysical matters that are to the fore in the rest of the Theaetetus , but also about questions of deep ethical significance. So, for instance, it can hardly be an accident that, at 176c2, the difference between justice and injustice is said to be a difference between knowledge ( gnôsis ) and ignorance ( agnoia ).

Another common question about the Digression is: does it introduce or mention the Platonic Forms? Certainly the Digression uses phrases that are indisputably part of the Middle-Period language for the Forms. If Plato uses the language of the theory of Forms in a passage which is admitted on all sides to allude to the themes of the Republic , it strains credulity to imagine that Plato is not intentionally referring to the Forms in that passage.

On the other hand, as the Revisionist will point out, the Theaetetus does not seem to do much with the Forms that are thus allegedly introduced. But perhaps it would undermine the Unitarian reading of the Theaetetus if the Forms were present in the Digression in the role of paradigm objects of knowledge. For the Unitarian reading, at least on the version that strikes me as most plausible, says that the aim of the Theaetetus is to show that, in the end, we cannot construct a theory of knowledge without the Forms—a claim which is to be proved by trying and failing, three times, to do so. So if the Forms were there in the Digression, perhaps that would be a case of “giving the game away.”

After the Digression Socrates returns to criticising Protagoras’ relativism. His last objection is that there is no coherent way of applying Protagoras’ relativism to judgements about the future.

How might Protagoras counter this objection? Protagoras has already suggested that the past may now be no more than whatever I now remember it to have been (166b). Perhaps he can also suggest that the future is now no more than I now believe it will be. No prediction is ever proved wrong, just as no memory is ever inaccurate. All that happens is it seems to one self at one time that something will be true (or has been true), and seems to another self at another time that something different is true.

But these appeals to distinctions between Protagorean selves—future or past—do not help. Suppose we grant to Protagoras that, when I make a claim about how the future will be, this claim concerns how things will be for my future self . It is just irrelevant to add that my future self and I are different beings. Claims about the future still have a form that makes them refutable by someone’s future experience. If I predict on Monday that on Tuesday my head will hurt, that claim is falsified either if I have no headache on Tuesday, or if, on Tuesday, there is someone who is by convention picked out as my continuant whose head does not hurt.

Similarly with the past. Suppose I know on Tuesday that on Monday I predicted that on Tuesday my head would hurt. It is no help against the present objection for me to reflect, on Tuesday, that I am a different person now from who I was then. My Monday-self can only have meant either that his head would hurt on Tuesday, which was a false belief on his part if he no longer exists on Tuesday; or else that the Tuesday-self would have a sore head. But if the Tuesday-self has no sore head, then my Monday-self made a false prediction, and so must have had a false belief. Either way, the relativist does not escape the objection.

Moreover, this defence of Protagoras does not evade the following dilemma. Either what I mean by claiming (to take an example of Bostock’s) that “The wine will taste raw to me in five years’ time” is literally that. Or else what I mean is just “ It seems to me that the wine will taste raw to me in five years’ time.”

Suppose I mean the former assertion. If the wine turns out not to taste raw five years hence, Protagoras has no defence from the conclusion that I made a false prediction about how things would seem to me in five years. Or suppose I meant the latter assertion. Then I did not make a prediction , strictly speaking, at all; merely a remark about what presently seems to me. Either way, Protagoras loses.

Socrates argues that if Heracleitus’ doctrine of flux is true, then no assertion whatever can properly be made. Therefore (a) Heracleitus’ theory of flux no more helps to prove that knowledge is perception than that knowledge is not perception, and (b) Heracleiteans cannot coherently say anything at all, not even to state their own doctrine.

There are two variants of the argument. On the first of these variants, evident in 181c2–e10, Socrates distinguishes just two kinds of flux or process, namely qualitative alteration and spatial motion, and insists that the Heracleiteans are committed to saying that both are continual. On the second variant, evident perhaps at 182a1, 182e4–5, Socrates distinguishes indefinitely many kinds of flux or process, not just qualitative alteration and motion through space, and insists that the Heracleiteans are committed to saying that every kind of flux is continual.

Now the view that everything is always changing in every way might seem a rather foolish view to take about everyday objects. But, as 182a2–b8 shows, the present argument is not about everyday objects anyway. Plato does not apply his distinction between kinds of change to every sort of object whatever, including everyday objects. He applies it specifically to the objects (if that is the word) of Heracleitean metaphysics. These items are supposed by the Heracleitean to be the reality underlying all talk of everyday objects. It is at the level of these Heracleitean perceivings and perceivers that Plato’s argument against Heracleitus is pitched. And it is not obviously silly to suppose that Heracleitean perceivings and perceivers are constantly changing in every way.

The argument that Socrates presents on the Heracleiteans’ behalf infers from “Everything is always changing in every way” that “No description of anything is excluded.” How does this follow? McDowell 1976: 181–2 finds the missing link in the impossibility of identifications . We cannot (says McDowell) identify a moving sample of whiteness, or of seeing, any longer once it has changed into some other colour, or perception.

But this only excludes re identifications: presumably I can identify the moving whiteness or the moving seeing until it changes, even if this only gives me an instant in which to identify it. This point renders McDowell’s version, as it stands, an invalid argument. If it is on his account possible to identify the moving whiteness until it changes , then it is on his account possible to identify the moving whiteness. But if that is possible, then his argument contradicts itself: for it goes on to deny this possibility.

Some other accounts of the argument also commit this fallacy. Compare Sayre’s account (1969: 94): “If no statement, either affirmative or negative, can remain true for longer than the time taken in its utterance, then no statement can be treated as either true or false, and the cause of communicating with one’s fellow beings must be given up as hopeless.”

Sayre’s argument aims at the conclusion “No statement can be treated as either true or false.” But Sayre goes via the premiss “Any statement remains true no longer than the time taken in its utterance.” If there are statements which are true, even if they are not true for very long, it is not clear why these statements cannot be treated as true, at least in principle (and in practice too, given creatures with the right sensory equipment and sense of time).

McDowell’s and Sayre’s versions of the argument also face the following objection. It is obvious how, given flux, a present-tense claim like “Item X is present” can quickly cease to be true, because e.g., “Item Y is present” comes to replace it. But it isn’t obvious why flux should exclude the possibility of past-tense statements like “Item X flowed into item Y between t 1 and t 2 ,” or of tenseless statements like “Item X is present at t 1 , item Y is present at t 2 .” As Bostock 1988: 105–6 points out, “So long as we do have a language with stable meanings, and the ability to make temporal distinctions, there is no difficulty at all about describing an ever-changing world.”

“So long as” : to make the argument workable, we may suggest that its point is that the meanings of words are exempt from flux. If meanings are not in flux, and if we have access to those meanings, nothing stops us from identifying the whiteness at least until it flows away. But if meanings are in flux too, we will have the result that the argument against Heracleitus actually produces at 183a5: anything at all will count equally well as identifying or not identifying the whiteness. “Unless we recognise some class of knowable entities exempt from the Heracleitean flux and so capable of standing as the fixed meanings of words, no definition of knowledge can be any more true than its contradictory. Plato is determined to make us feel the need of his Forms without mentioning them” (Cornford 1935, 99).

Socrates completes his refutation of the thesis that knowledge is perception by bringing a twelfth and final objection, directed against D1 itself rather than its Protagorean or Heracleitean interpretations. This objection says that the mind makes use of a range of concepts which it could not have acquired, and which do not operate, through the senses: e.g., “existence,” “sameness,” “difference.” So there is a part of thought, and hence of knowledge, which has nothing to do with perception. Therefore knowledge is not perception.

Unitarians and Revisionists will read this last argument against D1 in line with their general orientations. Unitarians will suggest that Socrates’ range of concepts common to the senses is a list of Forms. They will point to the similarities between the image of the senses as soldiers in a wooden horse that Socrates offers at 184d1 ff., and the picture of a Heracleitean self, existing only in its awareness of particular perceptions, that he drew at 156–160.

Revisionists will retort that there are important differences between the Heracleitean self and the wooden-horse self, differences that show that Heracleiteanism is no longer in force in 184–187. They will insist that the view of perception in play in 184–187 is Plato’s own non-Heracleitean view of perception. Thus Burnyeat 1990: 55–56 argues that, since Heracleiteanism has been refuted by 184, “the organs and subjects dealt with [in the Wooden Horse passage] are the ordinary stable kind which continue in being from one moment to the next.” On the other hand, notice that Plato’s equivalent for Burnyeat’s “organs and subjects” is the single word aisthêseis (184d2). On its own, the word can mean either “senses” or “sensings”; but it seems significant that it was the word Plato used at 156b1 for one of the two sorts of Heracleitean “offspring.” Plato speaks of the aisthêseis concealed “as if within a Wooden Horse” as pollai tines (184d1), “indefinitely many.” But while there are indefinitely many Heracleitean sensings , there are not, of course, indefinitely many senses . Indeed even the claim that we have many senses ( pollai ), rather than several ( enioi , tines ), does not sound quite right, either in English or in Greek. This is perhaps why most translators, assuming that aisthêseis means “senses,” put “a number of senses” for pollai tines aisthêseis . Perhaps this is a mistake, and what aisthêseis means here is “Heracleitean sensings.” If so, this explains how the aisthêseis inside any given Wooden Horse can be pollai tines.

If the aisthêseis in the Wooden Horse are Heracleitean sensings , not ordinary, un-Heracleitean senses , this supports the Unitarian idea that 184–187 is contrasting Heracleitean perceiving of particulars with Platonic knowing of the Forms (or knowing of particulars via , and in terms of , the Forms).

Another piece of evidence pointing in the same direction is the similarity between Plato’s list of the “common notions” at Theaetetus 186a and closely contemporary lists that he gives of the Forms, such as the list of Forms ( likeness , multitude , rest and their opposites) given at Parmenides 129d, with ethical additions at Parmenides 130b. There are also the megista genê (“greatest kinds”) of Sophist 254b–258e ( being , sameness , otherness , rest and change ); though whether these genê are Forms is controversial.

7. Second Definition ( D2 ): “Knowledge is True Judgement”: 187b–201c

151–187 has considered and rejected the proposal that knowledge is perception. Sometimes in 151–187 “perception” seems to mean “immediate sensory awareness”; at other times it seems to mean “judgements made about immediate sensory awareness.” The proposal that “Knowledge is immediate sensory awareness” is rejected as incoherent: “Knowledge is not to be found in our bodily experiences, but in our reasonings about those experiences” (186d2). The proposal that “Knowledge is judgement about immediate sensory awareness” raises the question how judgements, or beliefs, can emerge from immediate sensory awareness. Answering this question is the main aim in 187–201.

Empiricists claim that sensation, which in itself has no cognitive content, is the source of all beliefs, which essentially have cognitive content—which are by their very nature candidates for truth or falsity. So unless we can explain how beliefs can be true or false, we cannot explain how there can be beliefs at all. Hence Plato’s interest in the question of false belief. What Plato wants to show in 187–201 is that there is no way for the empiricist to construct contentful belief from contentless sensory awareness alone. The corollary is, of course, that we need something else besides sensory awareness to explain belief. In modern terms, we need irreducible semantic properties. In Plato’s terms, we need the Forms.

In pursuit of this strategy of argument in 187–201, Plato rejects in turn five possible empiricist explanations of how there can be false belief. In the First Puzzle (188a–c) he proposes a basic difficulty for any empiricist. Then he argues that no move available to the empiricist circumvents this basic difficulty, however much complexity it may introduce (the other four Puzzles: 188d–201b). The Fifth Puzzle collapses back into the Third Puzzle, and the Third Puzzle collapses back into the First. The proposal that gives us the Fourth Puzzle is disproved by the counter-examples that make the Fifth Puzzle necessary. As for the Second Puzzle, Plato deploys this to show how empiricism has the disabling drawback that it turns an outrageous sophistical argument into a valid disproof of the possibility of at least some sorts of false belief.

Thus 187–201 continues the critique of perception-based accounts of knowledge that 151–187 began. Contrary to what some—for instance Cornford—have thought, it is no digression from the main path of the Theaetetus . On the contrary, the discussion of false belief is the most obvious way forward.

As Plato stresses throughout the dialogue, it is Theaetetus who is caught in this problem about false belief. It is not Socrates, nor Plato. There is clear evidence at Philebus 38c ff. that false belief (at least of some sorts) was no problem at all to Plato himself (at least at some points in his career). Plato’s question is not “How on earth can there be false judgement?” Rather it is “What sort of background assumptions about knowledge must Theaetetus be making, given that he is puzzled by the question how there can be false judgement?”

Is it only false judgements of identity that are at issue in 187–201, or is it any false judgement? One interpretation of 187–201 says that it is only about false judgements of misidentification. Call this view misidentificationism . The main alternative interpretation of 187–201 says that it is about any and every false judgement. Call this view anti-misidentificationism . The present discussion assumes the truth of anti-misidentificationism; see Chappell 2005: 154–157 for the arguments.

I turn to the detail of the five proposals about how to explain false belief that occupy Stephanus pages 187 to 200 of the dialogue.

The first proposal about how to explain the possibility of false belief is the proposal that false belief occurs when someone misidentifies one thing as another. To believe or judge falsely is to judge, for some two objects O1 and O2 , that O1 is O2 .

How can such confusions even occur? Plato presents a dilemma that seems to show that they can’t. The objects of the judgement, O1 and O2 , must either be known or unknown to the judger x . Suppose one of the objects, say O1 , is unknown to x . In that case, O1 cannot figure in x ’s thoughts at all, since x can only form judgements using objects that he knows. So if O1 is not an object known to x , x cannot make any judgement about O1 . A fortiori, then, x can make no false judgement about O1 either.

If, on the other hand, both O1 and O2 are known to x , then x can perhaps make some judgements about O1 and O2 ; but not the false judgement that “ O1 is O2 .” If x knows O1 and O2 , x must know that O1 is O1 and O2 is O2 , and that it would be a confusion to identify them. So apparently false belief is impossible if the judger does not know both O1 and O2 ; but also impossible if he does know both O1 and O2 .

I cannot mistake X for Y unless I am able to formulate thoughts about X and Y . But I will not be able to formulate thoughts about X and Y unless I am acquainted with X and Y . Being acquainted with X and Y means knowing X and Y ; and anyone who knows X and Y will not mistake them for each other.

Why think this a genuine puzzle? There seem to be plenty of everyday cases where knowing some thing in no way prevents us from sometimes mistaking that thing for something else. One example in the dialogue itself is at 191b (cp. 144c5). It is perfectly possible for someone who knows Socrates to see Theaetetus in the distance, and wrongly think that Theaetetus is Socrates. The First Puzzle does not even get off the ground, unless we can see why our knowledge of X and Y should guarantee us against mistakes about X and Y . Who is the puzzle of 188a–c supposed to be a puzzle for ?

Some authors, such as Bostock, Crombie, McDowell, and White, think that Plato himself is puzzled by this puzzle. Thus Crombie 1963: 111 thinks that Plato advances the claim that any knowledge at all of an object O is sufficient for infallibility about O because he fails to see the difference between “being acquainted with X ” and “being familiar with X .” But to confuse knowing everything about X with knowing enough about X to use the name ‘ X ’ is really a very simple mistake. Plato would not be much of a philosopher if he made this mistake.

If (as is suggested in e.g. Chappell 2004, ad loc.) 187–201 is an indirect demonstration that false belief cannot be explained by empiricism (whether this means a developed philosophical theory, or the instinctive empiricism of some people’s common sense), then it is likely that the First Puzzle states the basic difficulty for empiricism, to which the other four Puzzles look for alternative solutions. The nature of this basic difficulty is not fully, or indeed at all, explained by the First Puzzle. We have to read on and watch the development of the argument of 187–201 to see exactly what the problem is that gives the First Puzzle its bite.

The second proposal says that false judgement is believing or judging ta mê onta , “things that are not” or “what is not.” Socrates observes that if “what is not” is understood as it often was by Greek thinkers, as meaning “nothing,” then this proposal leads us straight into the sophistical absurdity that false beliefs are the same thing as beliefs about nothing (i.e., contentless beliefs). But there can be no beliefs about nothing; and there are false beliefs; so false belief isn’t the same thing as believing what is not.

Some think the Second Puzzle a mere sophistry. Bostock 1988: 165 distinguishes two versions of the sophistry: “On one version, to believe falsely is… to believe what is not ‘just by itself’; on the other version, it is to believe what is not ‘about one of the things which are’”. The argument of the first version, according to Bostock, “is just that there is no such thing as what is not (the case); it is a mere nonentity. But just as you cannot perceive a nonentity, so equally you cannot believe one either.” Bostock proposes the following solution to this problem: “We may find it natural to reply to this argument by distinguishing… propositions [from] facts, situations, states of affairs, and so on. Then we shall say that the things that are believed are propositions, not facts… so a false belief is not directed at a non-existent.”

This raises the question whether a consistent empiricist can admit the existence of propositions. At least one great modern empiricist, Quine 1953: 156–7, thinks not. Plato agrees: he regards a commitment to the existence of propositions as evidence of Platonism, acceptance of the claim that abstract objects (and plenty of them) genuinely exist. So an explanation of false judgement that invoked entities called propositions would be unavailable to the sort of empiricist that Plato has in his sights.

Bostock’s second version of the puzzle makes it an even more transparent sophistry, turning on a simple confusion between the “is” of predication and the “is” of existence. As pointed out above, we can reasonably ask whether Plato made this distinction, or made it as we make it.

If the structure of the Second Puzzle is really as Bostock suggests, then the Second Puzzle is just the old sophistry about believing what is not (cp. Parmenides DK 29B8 , Euthydemus 283e ff., Cratylus 429d, Republic 477a, Sophist 263e ff.). Moreover, on this interpretation of the Second Puzzle, Plato is committed, in his own person and with full generality, to accepting (at least provisionally) a very bad argument for the conclusion that there can be no false belief. It would be nice if an interpretation of the Second Puzzle were available that saw it differently: e.g., as accepted by him only in a context where special reasons make the Second Puzzle very plausible in that context.

One such interpretation is defended e.g., by Burnyeat 1990: 78, who suggests that the Second Puzzle can only work if we accept the “scandalous analogy between judging what is not and seeing or touching what is not there to be seen or touched”: “A model on which judgements relate to the world in the same sort of unstructured way as perceiving or (we may add) naming, will tie anyone in knots when it comes to the question ‘What is a false judgement the judgement/ name of?’. The only available answer, when the judgement is taken as an unstructured whole, appears to be: Nothing.”

Notice that it is the empiricist who will most naturally tend to rely on this analogy. It is the empiricist who finds it natural to assimilate judgement and knowledge to perception, so far as he can. So we may suggest that the Second Puzzle is a mere sophistry for any decent account of false judgement, but a good argument against the empiricist account of false judgement that Plato is attacking. The moral of the Second Puzzle is that empiricism validates the old sophistry because it treats believing or judging as too closely analogous to seeing: 188e4–7. For empiricism judgement, and thought in general, consists in awareness of the ideas that are present to our minds, exactly as they are present to our minds. It cannot consist in awareness of those ideas as they are not ; because (according to empiricism) we are immediately and incorrigibly aware of our own ideas, it can only consist in awareness of those ideas as they are . Nor can judgement consist in awareness of ideas that are not present to our minds, for (according to empiricism) what is not present to our minds cannot be a part of our thoughts. Still less can judgement consist in awareness of ideas that do not exist at all.

The old sophists took false belief as “judging what is not”; they then fallaciously slid from “judging what is not,” to “judging nothing,” to “not judging at all,” and hence concluded that no judgement that was ever actually made was a false judgement. The empiricism that Plato attacks not only repeats this logical slide; it makes it look almost reasonable. The point of the Second Puzzle is to draw out this scandalous consequence.

Literally translated, the third proposal about how to explain the possibility of false belief says that false belief occurs “when someone exchanges ( antallaxamenos ) in his understanding one of the things that are with another of the things that are, and says is ” (189b12–c2).

Perhaps the best way to read this very unclear statement is as meaning that the distinctive addition in the third proposal is the notion of inadvertency . The point of Socrates’ argument is that this addition does not help us to obtain an adequate account of false belief because thought ( dianoia ) has to be understood as an inner process, with objects that we are always fully and explicitly conscious of. If we are fully and explicitly conscious of all the objects of our thoughts, and if the objects of our thoughts are as simple as empiricism takes them to be, there is simply no room for inadvertency. But without inadvertency, the third proposal simply collapses back into the first proposal, which has already been refuted.

The empiricist conception of knowledge that Theaetetus unwittingly brings forth, and which Socrates is scrutinising, takes the objects of thought to be simple mental images which are either straightforwardly available to be thought about, or straightforwardly absent. The First Puzzle showed that there is a general problem for the empiricist about explaining how such images can be confused with each other, or indeed semantically conjoined in any way at all. The Second Puzzle showed that, because the empiricist lacks clear alternatives other than that someone should have a mental image or lack it, he is wide open to the sophistical argument which identifies believing with having a mental image , and then identifies believing what is with having a mental image , too—and so “proves” the impossibility of false belief. The Third Puzzle restricts itself (at least up to 190d7) to someone who has the requisite mental images, and adds the suggestion that he manages to confuse them by a piece of inadvertency. Socrates’ rejoinder is that nothing has been done to show how there can be inadvertent confusions of things that are as simple and unstructured, and as simply grasped or not grasped, as the empiricist takes mental images to be. Just as speech is explicit outer dialogue, so thought is explicit inner dialogue. What the empiricist needs to do to show the possibility of such a confusion is to explain how, on his principles, either speech or thought can fail to be fully explicit and fully “in touch” with its objects, if it is “in touch” with them at all.

In the discussion of the Fourth and Fifth Puzzles, Socrates and Theaetetus together work out the detail of two empiricist attempts to explain just this. It then becomes clearer why Plato does not think that the empiricist can explain the difference between fully explicit and not-fully-explicit speech or thought. Plato thinks that, to explain this, we have to abandon altogether the empiricist conception of thought as the concatenation (somehow) of semantically inert simple mental images. Instead, we have to understand thought as the syntactic concatenation of the genuine semantic entities, the Forms . Mistakes in thought will then be comprehensible as mistakes either about the logical interrelations of the Forms, or about the correct application of the Forms to the sensory phenomena.

The Wax Tablet passage offers us a more explicit account of the nature of thought, and its relationship with perception. The story now on offer says explicitly that perception relates to thought roughly as Humean “impressions” relate to Humean “ideas” (191d; compare Hume, First Enquiry II). The objects of perception, as before, are a succession of constantly-changing immediate awarenesses. The objects of thought, it is now added, are those objects of perception to which we have chosen to give a measure of stability by imprinting them on the wax tablets in our minds. (The image of memory as writing in the mind had currency in Greek thought well before Plato’s time: see e.g. Aeschylus, Eumenides 275.)

This new spelling-out of the empiricist account of thought seems to offer new resources for explaining the possibility of false belief. The new explanation can say that false belief occurs when there is a mismatch, not between two objects of thought , nor between two objects of perception , but between one object of each type.

This proposal faces a simple and decisive objection. No one disputes that there are false beliefs that cannot be explained as mismatches of thought and perception: e.g., false beliefs about arithmetic. The Wax Tablet does not explain how such false beliefs happen; indeed it entails that they can’t happen. Such mistakes are confusions of two objects of thought, and the Wax Tablet model does not dispute the earlier finding that there can be no such confusions. So the Wax Tablet model fails.

There is of course plenty more that Plato could have said in criticism of the Wax Tablet model. Most obviously, he could have pointed out the absurdity of identifying any number with any individual’s thought of that number (195e9 ff.); especially when the numerical thought in question is no more than an ossified perception. In the present passage Plato is content to refute the Wax Tablet by the simplest and shortest argument available: so he does not make this point. But perhaps the point is meant to occur to the reader; for the same absurdity reappears in an even more glaring form in the Aviary passage.

If we had a solution to the very basic problem about how the empiricist can get any content at all out of sensation, then the fourth proposal might show how the empiricist could explain false belief involving perception. The fifth and last proposal about how to explain the possibility of false belief attempts to remedy the fourth proposal’s incapacity—which Plato says refutes it, 196c5–7—to deal with cases of false belief involving no perception, such as false arithmetical beliefs.

It attempts this by deploying a distinction between knowledge that someone merely has (latent knowledge) and knowledge that he is actually using (active knowledge) . (Perhaps Plato is now exploring “the intermediate stages between knowing and not knowing” mentioned at 188a2–3.) The suggestion is that false belief occurs when someone wants to use some item of latent knowledge in his active thought, but makes a wrong selection from among the items that he knows latently.

If this proposal worked it would cover false arithmetical belief. But the proposal does not work, because it is regressive. If there is a problem about the very possibility of confusing two things, it is no answer to this problem to suppose that for each thing there is a corresponding item of knowledge, and that what happens when two things are confused is really that the two corresponding items of knowledge are confused (200a–b).

The Aviary rightly tries to explain false belief by complicating our picture of belief. But it complicates in the wrong way and the wrong place. It is no help to complicate the story by throwing in further objects of the same sort as the objects that created the difficulty about false belief in the first place. What is needed is a different sort of object for thought: a kind of object that can be thought of under different aspects (say, as “the sum of 5 and 7,” or as “the integer 12”). There are no such aspects to the “items of knowledge” that the Aviary deals in. As with the conception of the objects of thought and knowledge that we found in the Wax Tablet, it is this lack of aspects that dooms the Aviary’s conception of the objects of knowledge too. Like the Wax Tablet, the Aviary founders on its own inability to accommodate the point that thought cannot consist merely in the presentation of a series of inert “objects of thought.” Whether these objects of thought are mental images drawn from perception or something else, the thinking is not so much in the objects of thought as in what is done with those objects (186d2–4).

We may illustrate this by asking: When the dunce who supposes that 5 + 7 = 11 decides to activate some item of knowledge to be the answer to “What is the sum of 5 and 7?,” which item of knowledge does he thus decide to activate? At first only two answers seem possible: either he decides to activate 12, or he decides to activate 11. If he decides to activate 12, then we cannot explain the fact that what he actually does is activate 11, except by saying that he mistakes the item of knowledge which is 11 for the item of knowledge which is 12. But this mistake is the very mistake ruled out as impossible right at the beginning of the inquiry into false belief (188a–c). Alternatively, if he decides to activate 11, then we have to ask why he decides to do this. The most plausible answer to that question is: “Because he believes falsely that 5 + 7 = 11.” But as noted above, if he has already formed this false belief, within the account that is supposed to explain false belief, then a regress looms.

In fact, the correct answer to the question “Which item of knowledge does the dunce decide to activate?” is neither “12” nor “11.” It is “ that number which is the sum of 5 and 7.” But this answer does not save the Aviary theorist from the dilemma just pointed out; for it is not available to him. To be able to give this answer, the Aviary theorist would have to be able to distinguish “that number which is the sum of 5 and 7” from “12.” But since “12” is “ that number which is the sum of 5 and 7,” this distinction cannot be made by anyone who takes the objects of thought to be simple in the way that the Aviary theorist seems to.

At 199e1 ff. Theaetetus suggests an amendment to the Aviary. This is that we might have items of ignorance in our heads as well as items of knowledge. As Socrates remarks, these ignorance-birds can be confused with knowledge-birds in just the same way as knowledge-birds can be confused with each other. So the addition does not help.

At 200d–201c Socrates argues more directly against D2 . He offers a counter-example to the thesis that knowledge is true belief. A skilled lawyer can bring jurymen into a state of true belief without bringing them into a state of knowledge; so knowledge and true belief are different states.

McDowell 1976: 227–8 suggests that this swift argument “contradicts the most characteristic expositions of the Theory of Forms, which indicate that the title ‘knowledge’ should be reserved for a relation between the mind and the Forms untainted by any reliance on perception.” By contrast Plato here tells us, quite unambiguously, that the jury are persuaded into a state of true belief “about things which only someone who sees them can know” (201b8). This implies that there can be knowledge which is entirely reliant on perception. (One way out of this is to deny that Plato ever thought that knowledge is only of the Forms, as opposed to thinking that knowledge is paradigmatically of the Forms. For this more tolerant Platonist view about perception see e.g. Philebus 58d–62d, and Timaeus 27d ff.)

The jury argument seems to be a counter-example not only to D2 but also to D3 , the thesis that knowledge is true belief with an account (provided we allow that the jury “have an account”).

A third problem about the jury argument is that Plato seems to offer two incompatible explanations of why the jury don’t know: first that they have only a limited time to hear the arguments (201b3, 172e1); and second that their judgement is second-hand (201b9).

8. Third Definition ( D3 ): “Knowledge is True Judgement With an Account”: 201d–210a

Theaetetus’ third proposal about how to knowledge is ( D3 ) that it is true belief with an account ( meta logou alêthê doxan ).

D3 apparently does nothing at all to solve the main problems that D2 faced. Besides the jurymen counter-example just noted, 187–201 showed that we could not define knowledge as true belief unless we had an account of false belief. This problem has not just evaporated in 201–210. It will remain as long as we propose to define knowledge as true belief plus anything. Significantly, this does not seem to bother Plato—as we might expect if Plato is not even trying to offer an acceptable definition of knowledge, but is rather undermining unacceptable definitions.

One crucial question about Theaetetus 201–210 is the question whether the argument is concerned with objectual or propositional knowledge. This is a basic and central division among interpretations of the whole passage 201–210, but it is hard to discuss it properly without getting into the detail of the Dream Theory: see section 8a.

A second question, which arises often elsewhere in the Theaetetus , is whether the argument’s appearance of aporia reflects genuine uncertainty on Plato’s part, or is rather a kind of literary device. Is Plato thinking aloud, trying to clarify his own view about the nature of knowledge, as Revisionists suspect? Or is he using an aporetic argument only to smoke out his opponents, as Unitarians think?

The evidence favours the latter reading. There are a significant number of other passages where something very like Theaetetus’ claim ( D3 ) that knowledge is “true belief with an account” is not only discussed, but actually defended: for instance, Meno 98a2, Phaedo 76b5–6, Phaedo 97d–99d2, Symposium 202a5–9, Republic 534b3–7, and Timaeus 51e5. So it appears that, in the Theaetetus , Plato cannot be genuinely puzzled about what knowledge can be. Nor can he genuinely doubt his own former confidence in one version of D3 . If he does have a genuine doubt or puzzle of this sort, it is simply incredible that he should say what he does say in 201–210 without also expressing it.

What Plato does in 201–210 is: present a picture (Socrates’ Dream) of how things may be if D3 is true (201c–202c); raise objections to the Dream theory which are said (206b12) to be decisive (202c–206c); and present and reject three further suggestions about the meaning of logos , and so three more versions of D3 (206c–210a). But none of these four interpretations of D3 is Plato’s own earlier version of D3 , which says that knowledge = true belief with an account of the reason why the true belief is true . If what Plato wants to tell us in Theaetetus 201–210 is that he no longer accepts any version of D3 , not even his own version, then it is extraordinary that he does not even mention his own version, concentrating instead on versions of D3 so different from Plato’s version as to be obviously irrelevant to its refutation.

Unitarians can suggest that Plato’s strategy is to refute what he takes to be false versions of D3 so as to increase the logical pressure on anyone who rejects Plato’s version of D3 . In particular, he wants to put pressure on the empiricist theories of knowledge that seem to be the main target of the Theaetetus . What Plato wants to show is, not only that no definition of knowledge except his own, D3 , is acceptable, but also that no version of D3 except his own is acceptable.

Rather as Socrates offered to develop D1 in all sorts of surprising directions, so now he offers to develop D3 into a sophisticated theory of knowledge. This theory, usually known as the “Dream of Socrates” or the “Dream Theory,” posits two kinds of existents, complexes and simples, and proposes that “an account” means “an account of the complexes that analyses them into their simple components.” Thus “knowledge of x ” turns out to mean “true belief about x with an account of x that analyses x into its simple components.”

Taken as a general account of knowledge, the Dream Theory implies that knowledge is only of complexes, and that there can be no knowledge of simples. Socrates attacks this implication.

A common question about the Dream Theory is whether it is concerned with objectual or propositional knowledge. Those who take the Dream Theory to be concerned with propositional knowledge include Ryle 1990: 27–30: “from 201 onwards Plato concentrates on ‘know’ ( connaître ): [Socrates’ Dream] is a logician’s theory, a theory about the composition of truths and falsehoods.” Those who take the Dream Theory to be concerned with objectual knowledge include White 1976: 177, and Crombie 1963: II: 41–42; also Bostock 1988. A third way of taking the Dream Theory, which may well be the most promising interpretation, is to take it as a Logical Atomism : as a theory which founds an account of propositional structure on an account of the concatenation of simple objects of experience or acquaintance such as “sense data.”

The Logical-Atomist reading of the Dream Theory undercuts the propositional/objectual distinction. On this reading, the Dream Theory claims that simple, private objects of experience are the elements of the proposition; thus, the Dream Theory is both a theory about the structure of propositions and a theory about simple and complex objects. It claims in effect that a proposition’s structure is that of a complex object made up out of simple objects, where these simple objects are conceived in the Russellian manner as objects of inner perception or acquaintance, and the complexes which they compose are conceived in the phenomenalist manner as (epistemological and/ or semantic) constructs out of those simple objects.

This supposition makes good sense of the claim that we ourselves are examples of complexes (201e2: “the primary elements ( prôta stoikheia ) of which we and everything else are composed…”). If the Dream theorist is a Logical Atomist, he will think that there is a clear sense in which people, and everything else, are composed out of sense data. He will also think that descriptions of objects, too, are complexes constructed in another way out of the immediately available simples of sensation.

For such a theorist, epistemology and semantics alike rest upon the foundation provided by the simple objects of acquaintance. Both thought and meaning consist in the construction of complex objects out of those simple objects. Philosophical analysis, meanwhile, consists in stating how the complexes involved in thought and meaning are constructed out of simples. This statement involves, amongst other things, dividing down to and enumerating the (simple) parts of such complexes.

What then is the relation of the Dream Theory to the problems posed for empiricism by the discussion of D2 in 187–201? The fundamental problem for empiricism, as we saw, is the problem how to get from sensation to content : the problem of how we could start with bare sense-data, and build up out of them anything that deserved to be called meaning . Plato thinks that there is a good answer to this, though it is not an empiricist answer. Sense experience becomes contentful when it is understood and arranged according to the structures that the Forms give it. So to understand sense experience is, in the truest sense, “to give an account” for it.

The empiricist cannot offer this answer to the problem of how to get from sensation to content without ceasing to be an empiricist. What the empiricist can do is propose that content arises out of sets of sense experiences. We get to the level of belief and knowledge only when we start to consider such sets: before that we are at the level only of perception. Our beliefs, couched in expressions that refer to and quantify over such sets, will then become knowledge (a) when they are true, and (b) when we understand the full story of their composition out of such sets.

If this is the point of the Dream Theory, then the best answer to the question “Whose is the Dream Theory?” is “It belongs to the empiricist whom Plato is attacking.”

The Dream Theory says that knowledge of O is true belief about O plus an account of O ’s composition. If O is not composite, O cannot be known, but only “perceived” (202b6).

Socrates’ main strategy in 202d8–206c2 is to attack the Dream’s claim that complexes and elements are distinguishable in respect of knowability. To this end he deploys a dilemma. A complex, say a syllable, is either (a) no more than its elements (its letters), or (b) something over and above those elements.

202d8–203e1 shows that unacceptable consequences follow from alternative (a), that a complex is no more than its elements. If I am to know a syllable SO , and that syllable is no more than its elements, then I cannot know the syllable SO without also knowing its elements S and O . Indeed, it seems that coming to know the parts S and O is both necessary and sufficient for coming to know the syllable SO . But if that is right, and if the letter/syllable relation models the element/complex relation, then if any complex is knowable , its elements will be knowable too; and if any complex’s elements are unknowable , then the complex will be unknowable too. This result contradicts the Dream Theory.

203e2–205e8 shows that unacceptable consequences follow from alternative (b), that a complex is something over and above its elements. In that case, to know the syllable is to know something for which knowledge of the elements is not sufficient. The syllable turns out to be “a single Idea that comes to be out of the fitted-together elements” (204a1–2). But then the syllable does not have the elements as parts: if it did, that would compromise its singularity. And if the elements are not the parts of the syllable, nothing else can be. So the syllable has no parts, which makes it as simple as an element. Thus if the element is unknowable, the syllable must be unknowable too. This result contradicts the Dream Theory too.

Finally, in 206a1–c2, Plato makes a further, very simple, point against the Dream Theory. Our own experience of learning letters and syllables shows that it is both more basic and more important to know elements than complexes, not vice versa as the Dream Theory implies. The thesis that the complexes are knowable, the elements unknowable, is false to our experience, in which “knowledge of the elements is primary” (Burnyeat 1990:192).

The refutation of the Dream Theory’s attempt to spell out what it might be like for D3 to be true is followed by three attempts to give an account of what a logos is. The first attempt to give an account of “account” takes logos just to mean “speech” or “statement.” This is deemed obviously insufficient (206c1–206e3).

A second attempted explanation of “ logos of O” takes it as “enumeration of the elements of O .” The logos is a statement of the elements of the object of knowledge. You have knowledge of something when, in addition to your true belief about it, you are able also to “go through the elements” of that thing.

Plato’s objection to this proposal (208b) is that it leaves open the possibility that someone could count as having knowledge of the name “Theaetetus” even if they could do no more than write out the letters of the name “Theaetetus” in the right order. Since such a person can enumerate the elements of the complex, i.e., the letters of the name (207c8–d1), he has an account. Since he can arrange those letters in their correct order (208a9–10), he also has true belief. For all that, insists Plato, he does not have knowledge of the name “Theaetetus.”

Why not, we might ask? To see the answer we should bring in what Plato says about syllables at 207d8–208a3. Suppose someone could enumerate the letters of “Theaetetus,” and could give their correct order, and yet knew nothing about syllables. This person wouldn’t count as knowing “Theaetetus” because he would have no understanding of the principles that get us from ordered letters to names. Those principles are principles about how letters form syllables, and how syllables form names. A person who can state only the letters of “Theaetetus” and their order has no awareness of these principles.

To put it a modern way, a robot or an automatic typewriter might be able to reproduce or print the letters of “Theaetetus” correctly and in order. It might even be able to store such a correct ordering in its electronic memory. That would not show that such a machine understood how to spell “Theaetetus,” any more than the symbol-manipulating capacities of the man in Searle’s Chinese Room show that he understands Chinese. What is missing is an awareness of bridging or structuring principles, rules explaining how we get from strings of symbols, via syllables, to representations of Greek names.

Knowledge of such bridging principles can reasonably be called knowledge of why the letters of “Theaetetus” are what they are. So it is plausible to suggest that the moral of the argument is to point us to the need for an account in the sense of an explanation “Why?,” and so to the version of D3 that Plato himself accepts.

The third proposed account of logos says that to give the logos of O is to cite the sêmeion or diaphora of O . In the Wax Tablet passage, sêmeion meant ‘imprint’; in the present passage, it means the ‘sign’ or diagnostic feature wherein x differs from everything else, or everything else of O ’s own kind. So, presumably, knowledge of (say) Theaetetus consists in true belief about Theaetetus plus an account of what differentiates Theaetetus from every other human.

Socrates offers two objections to this proposal. First, if knowledge of Theaetetus requires a mention of his sêmeion , so does true belief about Theaetetus. Second, to possess “an account of Theaetetus’ sêmeion ” must mean either (a) having true belief about that sêmeion, or else (b) having knowledge of it. But it has already been pointed out that any true belief, if it is to qualify as being about Theaetetus at all, must already be true belief about his sêmeion. So interpretation (a) has the result that knowledge of Theaetetus = true belief about Theaetetus’ sêmeion + true belief about Theaetetus’ sêmeion . As for (b): if we want to know what knowledge is, it is no help to be told that knowledge of O = something else + knowledge of the sêmeion of O . We still need to know what knowledge of the sêmeion of O is. Nor will it help us to be launched on a vicious regress: as we will be if we are told that knowledge of the sêmeion of O = something else + knowledge of the sêmeion of the sêmeion of O .

This is where the argument ends, and Socrates leaves to meet his accusers.

The Theaetetus is an extended attack on certain assumptions and intuitions about knowledge that the intelligent man-in-the-street—Theaetetus, for instance—might find initially attractive, and which some philosophers known to Plato—Protagoras and Heracleitus, for instance—had worked up into complex and sophisticated philosophical theories. Basic to all these assumptions and intuitions, which here have been grouped together under the name “empiricism,” is the idea that knowledge is constructed out of perception and perception alone.

The first part of the Theaetetus attacks the idea that knowledge could be simply identified with perception. Perceptions alone have no semantic structure. So if this thesis was true, it would be impossible to state it.

The second part attacks the suggestion that knowledge can be defined as true belief, where beliefs are supposed to be semantically-structured concatenations of sensory impressions. Against this Plato argues that, unless something can be said to explain how impressions can be concatenated so as to give them semantic structure, there is no reason to grant that the distinction between true and false applies to such beliefs any more than it does to perceptions.

Finally, in the third part of the Theaetetus , an attempt is made to meet this challenge, and present some explanation of how semantic structures can arise out of mere perceptions or impressions. The proposed explanation is the Dream Theory, a theory interestingly comparable to Russellian Logical Atomism, which takes both propositions and objects to be complexes “logically constructed” out of simple sensory impressions. On this conception, knowledge will come about when someone is capable not only of using such logical constructions in thought, but of understanding how they arise from perception.

Socrates’ basic objection to this theory is that it still gives no proper explanation of how this logical construction takes place. Without such an explanation, there is no good reason to treat the complexes that are thus logically constructed as anything other than simples in their own right. We need to know how it can be that, merely by conjoining perceptions in the right way, we manage to achieve a degree of semantic structure that (for instance) makes it possible to refer to things in the world , such as Theaetetus. But this is not explained simply by listing all the simple perceptions that are so conjoined. Nor—and this is where we reach the third proposal of 208b11–210a9—is it explained by fixing on any of those perceptions in particular, and taking it to be the special mark of Theaetetus whereby reference to Theaetetus is fixed.

The third proposal about how to understand logos faces the difficulty that, if it adds anything at all to differentiate knowledge of O from true belief about O , then what it adds is a diagnostic quality of O . If there is a problem about how to identify O , there is a problem about how to identify the diagnostic quality too. This launches a vicious regress.

One way of preventing this regress is to argue that the regress is caused by the attempt to work up a definition of knowledge exclusively out of empiricist materials. Hence there is no way of avoiding such a vicious regress if you are determined to try to define knowledge on an exclusively empiricist basis. The right response is to abandon that attempt. Knowledge is indeed indefinable in empiricist terms. In those terms, it has no logos . In those terms, therefore, knowledge itself is unknowable.

The official conclusion of the Theaetetus is that we still do not know how to define knowledge. Even on the most sceptical reading, this is not to say that we have not learned anything about what knowledge is like. As Theaetetus says (210b6), he has given birth to far more than he had in him.

And as many interpreters have seen, there may be much more to the ending than that. It may even be that, in the last two pages of the Theaetetus , we have seen hints of Plato’s own answer to the puzzle. Perhaps understanding has emerged from the last discussion, as wisdom did from 145d–e, as the key ingredient without which no true beliefs alone can even begin to look like they might count as knowledge. Perhaps it is only when we, the readers, understand this point—that epistemological success in the last resort depends on having epistemological virtue—that we begin not only to have true beliefs about what knowledge is, but to understand knowledge.

References to Plato’s Theaetetus follow the pagination and lineation of E.A.Duke, W.F.Hicken, W.S.M.Nicholl, D.B.Robinson, J.C.G.Strachan, edd., Platonis Opera Tomus I.

• Allen, R. E. (ed.), 1965, Studies in Plato’s Metaphysics , London: Routledge.
• Anonymous Commentator (“Anon”), 1905, Commentary on Plato’s Theaetetus , Diels and Schubart (eds.), Berlin: Berliner Klassikertexte II.
• Ast, F., 1816, Platons Leben und Schriften , Leipzig: Weidmann.
• Berkeley, G., 1744, Siris: A Chain of Philosophical Reflexions and Inquiries concerning the Virtues of Tar-Water , London: Innys, Hitch & Davis.
• Bostock, D., 1988, Plato’s Theaetetus , Oxford: Oxford University Press.
• Burnyeat, M.F., 1990, The Theaetetus of Plato , with a translation by Jane Levett, Hackett: Indianapolis.
• Campbell, L., 1883, The Theaetetus of Plato , Oxford: Oxford University Press.
• Castagnoli, Luca, 2010), Ancient Self-Refutation: The Logic and History of the Self-Refutation Argument from Democritus to Augustine , Cambridge: Cambridge University Press.
• Chappell, T.D.J., 1995, “Does Protagoras Refute Himself?,” Classical Quarterly , 45(2): 333–338.
• –––, 2005, Reading Plato’s Theaetetus , Indianapolis: Hackett.
• –––, 2006, “Reading the peritrope”, Phronesis , 51(2): 109–139.
• Cherniss, H., 1965, “The relation of the Timaeus to Plato’s Later Dialogues,” in H. Cherniss, Selected Papers , Leiden: Brill, 1977, 298–339.
• Cornford, F.M., 1935, Plato’s Theory of Knowledge , London: Routledge.
• Crombie, I., 1963, An Examination of Plato’s Doctrines , London: Routledge.
• Denyer, N., 1991, Language, Thought and Falsehood in Ancient Greek Philosophy , London: Routledge.
• Diès, A., 1923, Platon: Oeuvres Complètes , Paris: Belles Lettres. (The Theaetetus is in Volume VII, Part I.)
• Fine, Gail, 1979, “False belief in the Theaetetus ”, Phronesis , 24: 70–80.
• Fine, Gail, 1996, “Protagorean relativisms”, in J.Cleary and W.Wians (eds.), Proceedings of the Boston Area Colloquium in Ancient Philosophy , Lanham, MD: University Press of America, 211–243.
• Geach, P., 1966, “Plato’s Euthyphro ,” The Monist , 50: 369–382.
• Locke, J., 1689, Enquiry concerning Human Understanding , P. Nidditch (ed.), Oxford: Oxford University Press, 1975.
• Lutoslawski, W., 1905, Origin and Growth of Plato’s Logic , London: Longmans.
• McDowell, J., 1973, Plato’s Theaetetus , Oxford: The Clarendon Plato Series.
• Owen, G.E.L., 1965, “The place of the Timaeus in Plato’s Dialogues,” in G. E. L. Owen, Logic, Science, and Dialectic , M. Nussbaum (ed.), London: Duckworth, 1986, 65–84.
• Penner, T., and Rowe, C., 2005, Plato’s Lysis. Cambridge: Cambridge University Press.
• Proclus, 1965, Commentary on the First Alcibiades of Plato , William O’Neill, trans., Martinus Nijhoff: The Hague.
• Quine, W.V.O., 1953, From a Logical Point of View , Cambridge, Mass.: Harvard University Press.
• Robinson, R., 1950, “Forms and error in Plato’s Theaetetus ,” Philosophical Review , 59: 3–30.
• Ross, W.D., 1953, Plato’s Theory of Ideas , Oxford: Oxford University Press.
• Runciman, W., 1962, Plato’s Later Epistemology , Cambridge: Cambridge University Press.
• Russell, B., 1956, Lectures on Logical Atomism , in Logic and Knowledge , R.C. Marsh (ed.), London: Allen and Unwin, 175–282.
• Ryle, G., 1939, “Plato’s Parmenides ”, Mind , 48: 129–151.
• –––, 1960, “Letters and Syllables in Plato,” Philosophical Review , 69: 431–451.
• –––, 1966, Plato’s Progress , Bristol: Thoemmes Press 1990.
• –––, 1990, “Logical Atomism in Plato’s Theaetetus ,” Phronesis , 35: 21–46.
• Sayre, K., 1969, Plato’s Analytic Method , Chicago: University of Chicago Press.
• –––, 1983, Plato’s Late Ontology , Princeton: Princeton University Press.
• Schleiermacher, F., 1817–1828, Platons Werke , Berlin: Realschulbuchhandlung.
• Sedley, D., 2004, The Midwife of Platonism , Oxford: Oxford University Press.
• White, N.P., 1976, Plato on Knowledge and Reality , Indianapolis: Hackett.
• Wittgenstein, L., 1961, Tractatus Logico-Philosophicus , Pears and McGuinness (trans.), London: Routledge.
• Wittgenstein, L., 1958, The Blue and Brown Books , Oxford: Blackwell.

How to cite this entry . Preview the PDF version of this entry at the Friends of the SEP Society . Look up topics and thinkers related to this entry at the Internet Philosophy Ontology Project (InPhO). Enhanced bibliography for this entry at PhilPapers , with links to its database.

• Original texts of Plato’s Dialogues (Perseus Digital Library, Tufts University)

Plato | Plato: method and metaphysics in the Sophist and Statesman | Plato: middle period metaphysics and epistemology | Platonism: in metaphysics

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The authors and SEP editors would like to thank Branden Kosch for noticing a point of Greek grammar in need of correction.

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Essays About Knowledge: 5 Examples and 7 Prompts

Discover our guide with example essays about knowledge and helpful writing prompts to inspire you and assist with your next piece of writing.

Knowledge refers to information, facts, and skills acquired through education, life experience, and others. It’s critical in achieving power, wisdom, and respect as it lets us be conscious of our surroundings. Our knowledge sets us apart from others as we apply it to every aspect of our lives, such as problem-solving and skill development.

Since knowledge is a broad topic, it’s used in various writings, such as academic and personal essays . Before writing, ensure you understand the subject, know the proper format, and have the main points ready to add to your piece.

5 Essay Examples

1. long essay on knowledge by prasanna, 2. knowledge is power essay for students and children by anonymous on toppr.com, 3. importance of historical knowledge by kristopher fitzgerald, 4. knowledge is power – essay by kirti daga, 5. knowledge is a lifelong process and leads to inventions by ankita yadav, 1. what is knowledge, 2. the true meaning of knowledge is power, 3. the value of knowledge, 4. how to boost knowledge, 5. knowledge vs. wealth, 6. the effect of insufficient knowledge, 7. how does knowledge help me in my everyday life.

“If there is no knowledge or not acquiring knowledge, such a person is merely existing or surviving and not living. Because to live a life, we are bound to make decisions. An appropriate decision can be made if we have the proper knowledge to analyze the problem and decide it.”

Prasanna defines knowledge as a weapon, shield, and the key to life. It’s something that sustains our existence. She deems that apart from books, one can learn from other people, nature, and even things we think are too trivial to matter. Prasanna includes a quote from Alexander Pope to discuss the importance of having extensive knowledge.

She suggests that it’s essential to apply knowledge to enjoy all of its perks. But ultimately, Prasanna believes that while knowledge is limitless, people should prioritize filling their brains with the information they can share with others. You might also be interested in these essays about leadership .

“… We can say that true knowledge help [a] person to bloom. Also, it keeps people away from fights and corruption. Besides, knowledge brings happiness and prosperity to the nation. Above all, knowledge opens the door of success for everyone.”

In this essay, the author refers to knowledge as something that can create and destroy life and balance on the planet. Although many are educated, only a few know the importance of knowledge. The writer further lists some benefits of knowledge, such as making impossible ideas possible, avoiding repeated mistakes, and realizing the difference between good and evil. Ultimately, the author believes that knowledge makes a person richer than billionaires because, unlike money, no one can steal knowledge.  

“Understanding our past is vitally important to the present and future of our civilization. We must find out to grow from our previous successes and errors. It is humanity to make errors, however the less we make, the stronger and smarter we end up being.”

Fitzgerald explains that understanding history is essential to learning from past mistakes. He points to the results of past failures recorded in books, such as death and damages. In addition, historical knowledge improves our lifestyle through modern technologies and efforts to restore the environment.

By studying the history of the world, people can understand the differences in customs and beliefs of different religions. This knowledge gives way to acceptance and appreciation, which are critical to avoiding conflicts originating from ignorant perceptions.

“Knowledge is power because it is intangible whereas money is tangible. An individual with knowledge is better than a fool with money because money cannot buy knowledge whereas knowledge can carve a part which will ultimately help in gaining loads and loads of money.”

In her essay, Daga provides two situations demonstrating how knowledge is more valuable than money. First, she states that wealth, skills, resources, and talent are useless if one doesn’t have the proper knowledge to use them. Meanwhile, even if you have few skills but are knowledgeable enough in a particular field, you have a higher chance of succeeding financially.

The essay also contains information about general knowledge vital to achieving life goals. It incorporates ways to gain knowledge, including reading books and newspapers, watching the latest news, and networking with people. 

“The whole life we learn and gain knowledge. Knowledge increases day by day. We work on the process of learning to gain more knowledge.”

Yadav relates knowledge to something that makes life beautiful. However, unlike an ordinary ornament, knowledge isn’t easily acquired. Knowledge is a lifelong process that people get from experiences, media, books, and others. It has many benefits, such as creating new inventions that improve society and the country. Yadav concludes her essay by saying that knowledge is a valuable asset. It assists people in achieving life goals and honing their moral values.

7 Prompts for Essays About Knowledge

There are many essays that define the word “knowledge”, you can use this prompt to explain the concept of knowledge in your own words. First, explain its textbook definition briefly, then analyze it using your own words and understanding. To conclude your piece, write about how you intend to use knowledge in your life. 

“Knowledge is power” is a famous quotation from Francis Bacon in his book Neues Organon. It’s a powerful quote that sparked various interpretations. For this prompt, you can compile meanings you see online or interview people on what they think the quote means. Then, compare it with the actual intention and origin of the citation.

Tip : Remember to add your analysis and ask the readers to create their interpretation to involve them in the discussion.

Continuous learning makes us better individuals and opens more opportunities for us. When we do what we can to collect knowledge from various media, we also feel a sense of accomplishment. For this prompt, list the reasons why you want to enrich your knowledge. Use this prompt to show the good and bad sides of cultivating knowledge by including what can happen if an individual applies their knowledge to do despicable things. 

You don’t need to follow a strict program or enroll in top universities to build your knowledge. In this essay, enumerate easy ways to enhance someone’s knowledge, such as having a healthy curiosity, being a reasonable observer and listener, and attending gatherings to socialize. Write down all the possible ways and tools someone needs to acquire more knowledge. Then, explain why it’s essential never to stop learning new things.

At the start of your essay, ask your readers what they prefer: Extensive knowledge or ample wealth? Some will choose knowledge because money runs out quickly. They will argue that knowing how to handle cash will help secure and grow their finances. On the other hand, others will choose wealth and insist that they can hire people to manage their sizable assets. Share what your thoughts are on the question and answer it as well. You can look for surveys, interviews, and other research materials to gather data that can support your reasoning.

Identify the effects of having insufficient knowledge about a specific topic or in general terms. Add any negative results that can stem from this deficiency. Then, discuss why people need to get more knowledge today. For example, people automatically believe what they see on social media without fact-checking.

Tip : You can include steps the government and organizations should take to provide people with the correct information to avoid false claims.

For this essay topic, describe how knowledge assists you in your day-to-day life and enhances your experiences. Ensure to tackle how knowledge plays a part in your decision-making and your pathway in life.

For instance, you watched a documentary about greenhouse gasses and learned about light pollution. So, on bright mornings, you turn off all the lights in your house to decrease your bill and protect the environment .

If you want to use the latest grammar software for your paper, read our guide to using an AI grammar checker.

Maria Caballero is a freelance writer who has been writing since high school. She believes that to be a writer doesn't only refer to excellent syntax and semantics but also knowing how to weave words together to communicate to any reader effectively.

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Definition Essay

Definition Essay - Writing Guide, Examples and Tips

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Published on: Oct 9, 2020

Last updated on: Jan 31, 2024

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Many students struggle with writing definition essays due to a lack of clarity and precision in their explanations.

This obstructs them from effectively conveying the essence of the terms or concepts they are tasked with defining. Consequently, the essays may lack coherence, leaving readers confused and preventing them from grasping the intended meaning.

But don’t worry!

In this guide, we will delve into effective techniques and step-by-step approaches to help students craft an engaging definition essay.

Continue reading to learn the correct formation of a definition essay. 

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What is a Definition Essay?

Just as the name suggests, a definition essay defines and explains a term or a concept. Unlike a narrative essay, the purpose of writing this essay is only to inform the readers.

Writing this essay type can be deceivingly tricky. Some terms, concepts, and objects have concrete definitions when explained. In contrast others are solely based on the writer’s understanding and point of view.

A definition essay requires a writer to use different approaches when discussing a term. These approaches are the following:

• Denotation - It is when you provide a literal or academic definition of the term.
• Connotation - It is when the writer provides an implied meaning or definition of the term.
• Enumeration - For this approach, a list is employed to define a term or a concept.
• Analogy - It is a technique in which something is defined by implementing a comparison.
• Negation - It is when you define a term by stating what it is not.

A single or combination of approaches can be used in the essay. 

Definition Essay Types

There are several types of definition essays that you may be asked to write, depending on the purpose and scope of the assignment. 

In this section, we will discuss some of the most common types of definition essays.

Descriptive Definition Essay 

This type of essay provides a detailed description of a term or concept, emphasizing its key features and characteristics. 

The goal of a descriptive definition essay is to help readers understand the term or concept in a more profound way.

Stipulative Definition Essay 

In a stipulative definition essay, the writer provides a unique definition of a term or concept. This type of essay is often used in academic settings to define a term in a particular field of study. 

The goal of a stipulative definition essay is to provide a precise and clear definition that is specific to the context of the essay.

Analytical Definition Essay 

This compare and contrast essay type involves analyzing a term or concept in-depth. Breaking it down into its component parts, and examining how they relate to each other. 

The goal of an analytical definition essay is to provide a more nuanced and detailed understanding of the term or concept being discussed.

Persuasive Definition Essay 

A persuasive definition essay is an argumentative essay that aims to persuade readers to accept a particular definition of a term or concept.

The writer presents their argument for the definition and uses evidence and examples to support their position.

Explanatory Definition Essay 

An explanatory definition essay is a type of expository essay . It aims to explain a complex term or concept in a way that is easy to understand for the reader. 

The writer breaks down the term or concept into simpler parts and provides examples and analogies to help readers understand it better.

Extended Definition Essay 

An extended definition essay goes beyond the definition of a word or concept and provides a more in-depth analysis and explanation. 

The goal of an extended definition essay is to provide a comprehensive understanding of a term, concept, or idea. This includes its history, origins, and cultural significance. 

How to Write a Definition Essay?

Writing a definition essay is simple if you know the correct procedure. This essay, like all the other formal pieces of documents, requires substantial planning and effective execution.

The following are the steps involved in writing a definition essay effectively:

Instead of choosing a term that has a concrete definition available, choose a word that is complicated . Complex expressions have abstract concepts that require a writer to explore deeper. Moreover, make sure that different people perceive the term selected differently. 

Once you have a word to draft your definition essay for, read the dictionary. These academic definitions are important as you can use them to compare your understanding with the official concept.

Drafting a definition essay is about stating the dictionary meaning and your explanation of the concept. So the writer needs to have some information about the term.

In addition to this, when exploring the term, make sure to check the term’s origin. The history of the word can make you discuss it in a better way.

Coming up with an exciting title for your essay is important. The essay topic will be the first thing that your readers will witness, so it should be catchy.

Creatively draft an essay topic that reflects meaning. In addition to this, the usage of the term in the title should be correctly done. The readers should get an idea of what the essay is about and what to expect from the document.

Now that you have a topic in hand, it is time to gather some relevant information. A definition essay is more than a mere explanation of the term. It represents the writer’s perception of the chosen term and the topic.

So having only personal opinions will not be enough to defend your point. Deeply research and gather information by consulting credible sources.

The gathered information needs to be organized to be understandable. The raw data needs to be arranged to give a structure to the content.

Here's a generic outline for a definition essay:

Are you searching for an in-depth guide on crafting a well-structured definition essay?Check out this definition essay outline blog!

6. Write the First Draft

Drafting each section correctly is a daunting task. Understanding what or what not to include in these sections requires a writer to choose wisely.

The start of your essay matters a lot. If it is on point and attractive, the readers will want to read the text. As the first part of the essay is the introduction , it is considered the first impression of your essay.

To write your definition essay introduction effectively, include the following information:

• Start your essay with a catchy hook statement that is related to the topic and the term chosen.
• State the generally known definition of the term. If the word chosen has multiple interpretations, select the most common one.
• Provide background information precisely. Determine the origin of the term and other relevant information.
• Shed light on the other unconventional concepts and definitions related to the term.
• Decide on the side or stance you want to pick in your essay and develop a thesis statement .

After briefly introducing the topic, fully explain the concept in the body section . Provide all the details and evidence that will support the thesis statement. To draft this section professionally, add the following information:

• A detailed explanation of the history of the term.
• Analysis of the dictionary meaning and usage of the term.
• A comparison and reflection of personal understanding and the researched data on the concept.

Once all the details are shared, give closure to your discussion. The last paragraph of the definition essay is the conclusion . The writer provides insight into the topic as a conclusion.

The concluding paragraphs include the following material:

• Summary of the important points.
• Restated thesis statement.
• A final verdict on the topic.

7. Proofread and Edit

Although the writing process ends with the concluding paragraph, there is an additional step. It is important to proofread the essay once you are done writing. Proofread and revise your document a couple of times to make sure everything is perfect.

Before submitting your assignment, make edits, and fix all mistakes and errors.

If you want to learn more about how to write a definition essay, here is a video guide for you!

Definition Essay Structure 

The structure of a definition essay is similar to that of any other academic essay. It should consist of an introduction, body paragraphs, and a conclusion. 

However, the focus of a definition essay is on defining and explaining a particular term or concept. 

In this section, we will discuss the structure of a definition essay in detail.

Introduction 

Get the idea of writing an introduction for a definition essay with this example:

Body Paragraphs

Here is an example of how to craft your definition essay body paragraph:

Types of the Term/Concept 

If applicable, the writer may want to include a section that discusses the different types or categories of the term or concept being defined. 

This section should explain the similarities and differences between the types, using examples and anecdotes to illustrate the points.

Examples of the Term/Concept in Action 

The writer should also include real-life examples of the term or concept being defined in action. 

This will help the reader better understand the term or concept in context and how it is used in everyday life.

Conclusion 

This example will help you writing a conclusion fo you essay:

Definition Essay Examples

It is important to go through some examples and samples before writing an essay. This is to understand the writing process and structure of the assigned task well.

Following are some examples of definition essays to give our students a better idea of the concept. 

Understanding the Definition Essay

Definition Essay Example

Definition Essay About Friendship

Definition Essay About Love

Family Definition Essay

Success Definition Essay

Beauty Definition Essay

Definition Essay Topics

Selecting the right topic is challenging for other essay types. However, picking a suitable theme for a definition essay is equally tricky yet important. Pick an interesting subject to ensure maximum readership.

If you are facing writer’s block, here is a list of some great definition essay topics for your help. Choose from the list below and draft a compelling essay.

• Authenticity
• Sustainability
• Mindfulness

Here are some more extended definition essay topics:

• Social media addiction
• Ethical implications of gene editing
• Personalized learning in the digital age
• Ecosystem services
• Cultural assimilation versus cultural preservation
• Sustainable fashion
• Gender equality in the workplace
• Financial literacy and its impact on personal finance
• Ethical considerations in artificial intelligence
• Welfare state and social safety nets

Need more topics? Check out this definition essay topics blog!

Definition Essay Writing Tips

Knowing the correct writing procedure is not enough if you are not aware of the essay’s small technicalities. To help students write a definition essay effortlessly, expert writers of CollegeEssay.org have gathered some simple tips.

These easy tips will make your assignment writing phase easy.

• Choose an exciting yet informative topic for your essay.
• When selecting the word, concept, or term for your essay, make sure you have the knowledge.
• When consulting a dictionary for the definition, provide proper referencing as there are many choices available.
• To make the essay informative and credible, always provide the origin and history of the term.
• Highlight different meanings and interpretations of the term.
• Discuss the transitions and evolution in the meaning of the term in any.
• Provide your perspective and point of view on the chosen term.

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Essay on Knowledge for Students and Children

500+ words essay on knowledge.

Knowledge is understanding and awareness of something. It refers to the information, facts, skills, and wisdom acquired through learning and experiences in life. Knowledge is a very wide concept and has no end. Acquiring knowledge involves cognitive processes, communication, perception, and logic. It is also the human capacity to recognize and accept the truth. Knowledge can be used for positive as well as negative purposes. Thus knowledge can create and destroy at the same time. One may use knowledge for personal progress as well as the progress of the community, city, state, and nation. Some may use it for negative purposes that may not only harm individuals but can also harm the community.

Importance of Knowledge

* Knowledge is a success – In today’s world without education and the power of knowledge, it is not possible to succeed in life or even keep up with the fast-paced life. It is not just enough to have knowledge on a particular subject to succeed but it is also important to have knowledge about how to use it effectively to succeed. One should have knowledge about various aspects of a subject.

* Personal Development- Knowledge can last for a lifetime and it impacts our growth which influences everything in our life from relationships to work. Knowledge is important for personal growth and development . We can gain knowledge on everything that we find interesting like any dance form, art, architecture, history or just about anything for our personal development. It makes us wise enough to independently make our decisions in life. But it is important to adopt a positive mindset to become a constant learner only then it helps us progress and achieve our goals.

* Knowledge solves problems – problems in life which can be solved with the power of knowledge. Knowledge sharpens our skills like reasoning and problem-solving . A strong base of knowledge helps brains function more smoothly and effectively. We become smarter with the power of knowledge and solve problems more easily.

* Everyday Life- Knowledge is important and useful in day to day events. For example, if I have to buy air tickets online, I need to have knowledge about the various sites and their discounts, their terms & conditions or like online banking. If I don’t have knowledge then I end up paying more. So gaining knowledge is a constant process and is useful every single day.

Get the huge list of more than 500 Essay Topics and Ideas

The process to increase knowledge

Open-Minded- We always learn something new by building on the knowledge that we have. We must always be open to accepting knowledge or information from anywhere we get. It may be from books, virtual media, friends, etc. To move on from one step to another we need to know more. Like in school we start from LKG, KG and then move on to 1st standard, 2nd standard and so on. It builds a strong base.

Reading Magazines- Reading helps to decode text and improves fluency to pronounce the speech sounds clear. Reading gives an idea about different topics and different views about them. One can get the actual global knowledge. Apart from that one can learn many new terms and phrase.

Communication- Shared knowledge allows you to communicate. Shared knowledge is important for communicating and understanding each other. When we discuss a certain topic with classmates, friends or relatives they have certain knowledge about it. So through communication, we get new ideas, facts and develops our knowledge. We can also identify what have we learned and what still we don’t know that helps us to clear our doubts later.

Watch documentaries or educational videos-  Discovery Channel, for example, provides excellent documentaries that keep you engaged. If you don’t like reading, this is an excellent alternative to getting your daily dose of knowledge while still relaxing in your couch!

The more knowledge we have the more power we possess. It is important for our personal and professional development and leads us to achieve success in life. Knowledge helps us in several ways but the best part is that it helps us understand ourselves as well as those around us better. It also helps us act wisely in different situations

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IB Theory of Knowledge (TOK) Vocabulary: The Complete Guide

by  Antony W

January 9, 2024

Theory of Knowledge has many terminologies and concepts that take time to understand. However, you don’t have to study and memorize all the IB TOK vocabulary words only a few of them are applicable to the assessment components.

So, in this guide, we’ve put together a list of only the most relevant TOK vocabularies that you need to be familiar with to pass your Theory of Knowledge Essay and Theory of Knowledge Exhibition.

To be clear, this guide contains only the most relevant terms you need to know about, some with links to related posts where you can learn more about the respective TOK subject.

Our goal with this list is simple. We want to keep you from trawling through hundreds of phrases and becoming overwhelmed by convoluted explanations.

TOK Vocabularies: The Only Terminologies You Need to Know

The following are the TOK vocabularies that matter the most in the Theory of Knowledge course: 

Truth is one of the most contentious topics in TOK, as no one can agree on what it is, but there are different theories that can make it easier for you to have a sense of how complicated the “truth” is. 

1. Truth based on statements that come together

Assume you're sitting in your bedroom and hear a kitchen 'drip, drip, drip'. Your sister, who arrives in the corridor, likewise hears the same 'drip, drip, drip' and inquires, "Did you leave the tap on?"

You proceed to check kitchen tap, which is definitely dripping due to the water not being completely turned off.

Three factors establish the veracity of this situation:

• You heard the tap leaking
• Your sister heard the tap dripping
• You saw the tap dripping.

These three assertions "coincide," and hence constitute the truth.

2. A truth that depicts reality

According to the Correspondence Theory of Truth , truth depends on your current situation. For example, if it’s raining outside and someone asks, “Is it raining?” there can only be one “true” response: yes, it’s raining outside. 

3. Truth based on your belief

One of your friends may strongly feel that money is the key to happiness, whereas your dad may fervently believe that teaching is the finest career choice for her. These are all extremely true for those who believe them, and hence may "truth."

In TOK and philosophy, knowledge is a theoretical or practical comprehension of a subject. Plato defined knowledge as justified genuine belief. According to his theory, knowledge is objective and founded on true assertions about real objects.

Philosophers concur on the existence of at least four distinct categories of knowledge:

• Logical knowledge derived from the logical relationships between concepts and interactions compatible with logic's norms.
• Semantic knowledge derived from the definition of words (semantics). In other words, from the commonly recognized definitions of the terms used to define Forms.
• Mathematics and geometry are the sources of systemic knowledge gained through time, education and research.
• The five senses provide empirical information.

You can click here to read more about the Plato’s Theory of Knowledge.

Ways of Knowing

Ways of Knowing in Theory of Knowledge refers to the approaches an individual use to attempt to understand how or why something occurs. There are 8 ways of knowing, each of which you can employ independently as a means to perceive the environment. These are:

• Sense perception
• Imagination

Ways of knowing are critical components because they enable you to obtain fundamental information and understanding about the world around you, which you may then develop into knowledge. 

Areas of Knowledge

Areas of Knowledge are distinct areas of thoughts concerned with how groups think. There are eight AOKs:

• Mathematics
• Natural Sciences
• Religious Knowledge
• Indigenous knowledge

All Areas of Knowledge include historical discoveries and innovations, disagreements between specialists in the subject, disagreements between professionals and the broader public, paradigm changes, and information passed down through generations.

Shared Knowledge

When you're in a group, some thoughts and views are acceptable to a majority, if not to all, members. This knowledge is disseminated among group members and is therefore considered 'shared'.

Take our planet, for example. Many people worldwide accept that "the planet is round”. Few people reach this conclusion on their own and rely heavily on the acceptance and subsequent dissemination of this knowledge by their group members.

Personal Knowledge

There’s a small difference between shared and personal knowledge, but it’s critical.

Personal knowledge is the information that an individual accepts and believes, often based on personal experiences that occurred in the absence of other individuals.

For instance, you would be the only one on the planet who understands why your favorite mug shattered, as you were the only one who witnessed it fall from the counter to the floor.

Paradigm Shift

Paradigm shift refers to a significant change that takes place in one of the Areas of Knowledge. This can relate to a significant shift in the way people do or understand things.

• A paradigm shift in the manner in which someone does something: The transition from photographic film to digital photography fundamentally altered the way people took photographs.
• A paradigm shift in how one understands something: The transition from Newtonian to Quantum Mechanics marked a sea change in how people understood physics.

A premise is a fundamental assertion upon which you build an argument and serves as the foundation for all arguments in logic. A premise needs not be true.

Empirical Knowledge

Empiricism is a term that refers to justification derived from experience, which indicates that empirical knowledge results from observation, experimentation, and direct contact with the senses.

Rationalism

This is a philosophical perspective according to which reason is the primary source and arbiter of truth and knowledge.

In this situation, truth is deductive and derived from logical conclusions established by intuition or innate knowledge based on a set of guiding axioms.

Also known as truth criteria, these are standards used to determine the accuracy of assertions and claims. There are three primary tests of truth:

• The coherence test determines if something makes sense, fits together (coheres), and is reasonable.
• Correspondence examination looks at the available evidence and reasoning.
• The pragmatic test examines a subject matter's practical utility and workability.

Need Help With IB Theory of Knowledge Assignment? 

Theory of knowledge is wide and complex. These TOK terms and their meanings are just a scratch on the surface of the whole area, and you will typically need many hours of reading and researching to even get an idea of what it is about. 

If you have a pending Theory or Knowledge assignment or project that is stressing you out, we can help you write it at a  pocket-friendly price . 

Help for Assessment is a team of premier experts in IB TOK essay writing, and we are ready to write your TOK assignment for you at the most student-friendly rates. All you have to do is order the TOK service here.  

About the author 

Antony W is a professional writer and coach at Help for Assessment. He spends countless hours every day researching and writing great content filled with expert advice on how to write engaging essays, research papers, and assignments.