II. Epistemology [Theory of Knowledge]

Epistemology is the philosophical investigation of knowledge. There is no question that knowledge is really good - vital for survival and success. But you are not aware, perhaps, that knowledge is more elusive than you think, and certain philosophers have doubted that certain knowledge is possible at all. This sounds puzzling, but realize this: The survival of animals - and of the human animal - in an evolutionary sense does not require certain knowledge. For everyday life purposes, too, 99% certainty - the relative certainty we have if something has happened in 99 of 100 previous instances - is enough. And yet, knowledge, properly speaking, must mean 'certain knowleddge' if it means anything at all. How is that? Think of this: If you found out that you were wrong about something, you will have to say, logically, that you thought you knew but now realize that you did not really know what you turned to be mistaken about. In other words, knowledge means that error is impossible - knowledge requires incorrigibility [impossibility of correcting what you 'know' - because if there is error in what you think you know, then, you don't really know.] It is surprising, and sombering, to realize that we live everyday life without having - and without needing - knowledge. Justified true opinion suffices. You will see what I mean by claiming that knowledge is impossible in everyday life - this will become clear as you read Descartes' Meditations and Russell on the problem of Induction. For the moment, think of the following: Your everyday beliefs are neither indibitable nor incorrigible - they can be doubted and can be corrected. You never reach the point in which you can have absolute certainty in the sense that you can no longer doubt or ever need to correct what you believe. If you ever reached that point, movement and change would have to cease. Moreover, as Descartes points out, there is always the possibility that what you take for real is not real - think here of the 'Matrix,' or of the possibility of dreaming or being deceived across the board and on a massive scale. We have had difficulties when we tried to develop criteria that would enable us to tell, with 100% certainty, that an event is real rather than induced in a 'virtual reality' fashion. Obviously, we don't need to worry about all this - but realize that what is at stake is 100% certainty, which, by definition, means knowledge. How can there be knowledge, considering that the next moment is unpredictable, and we are not certain about how we could independently verify the reality of what we take for real - independently means that you could be certain that what you believe as real is indeed real: since it is you who has to do the confirming, how can you know that you are still not deceived in this second confirmation step? Nor are our senses to be relied upon for 100% certainty: they have 'lied' to us before - they have deceived us about sticks that bend when immersed in water, and about 'Hollywood barns' and about many other things; and, moreover, the object of the senses is the mutable ever-changing world; an undpredictable world; a world we can only understand to the extent we are able to understand - and how could we independently verify this?

Difference between Knowledge and Opinion

So, we can state the difference between knowledge and opinion now. Knowledge does not admit of the possibility of error - knowledge is certain; opinion or belief might always be in error - it is not and cannot be 100% certain.

True Opinion and Knowledge

What about opinions we take pains to confirm - and such opinions turn out to be true after all, don't they? Well, are you sure? Let's take a famous example - conceived by no other than Bertrand Russell himself. Suppose that, one bright morning, you are rushing to work and you check out the ancient clock at the center of downtown. It says 9:00 exactly. You cannot be certain of course. But, then, you begin to ask everyone around you. They all say that it is indeed 9:00 by their watches. Still, they could be mistaken - by some uncanny and unlikely coincidence, all their watches could be wrong - and pointing to the exact same time. This is extremely unlikely but not impossible. But, suppose you have access to the official service that announces the time - so you finally confirm that it is nine o'clock, and ther eis no doubt about it. So, now, you have a true belief - your belief that the clock downtown has the right time is confirmed. It is, furthermore, a justified true belief - one that has been confirmed by a reasonable and rigorous process. But, here is what Russell suggests: What if the big clock had stopped exactly 24 - or 12- hours ago? So, you cannot really say that you KNOW that the clock has not stopped. This is an apt illustration of how even justified true belief [JTB] is still not the same as knowledge. Here is another example: Suppose that you buy a lottery ticket. Your chances of winning are one in ten thousand. So, you tell yourself, 'I know that I am not going to win.' And, indeed, you don't win. Your belief turns out to be true, and it is justified on the basis of the odds, which were against your winning. But, still, don't we think that you used the word 'know' inappropriately when you said that you 'knew' you were not going to win? There was still a 1/10,000 chance that you would win. It was extremely unlikely but it was not impossible. You did not KNOW that you were not going to win.

But, at least, you know now that you have not won - right? If you are thinking of the statement - 'since it turned I have not won, then, I have not won' - then, of course, you know this. But notice that this is an analytic truth - it does not give you any real information. If you are asking, 'is it possible that I have still won even though I believe that I have not won,' then, it is indeed possible that you are being deceived. Notice: the chances that something so odd and exotic is the case might be extremely small - but it is not impossible!

Necessary Truths

There are truths - true statements - that are necessary: they cannot be otherwise. Applied to such statements, knowing does make sense. Where do we find such statements, at last? Well, think here of geometry. A theorem is something you prove in geometry: you could not be mistaken about that! Of course, you can still make mistakes in geometry - but then YOU would be mistaken, not geometry. Think here also of the statement '2+3=5.' How can there ever be any doubt about that? Put {II} and {III} together and you always get {II III} - always. In a thousand years from now, we are sure that two oranges and three apples will five pieces of fruit - anywhere, under any circumstances, for anyone who is performing this operation. [Keep this example in mind. These are truths about which there can be no mistake. You are tempted to say that they must be analytic - statements like 'a bald man is bald', which are necessarily true but empty of any real information. You will find later in the course that Kant actually denies that such statements are empty of information. But you need to wait for this.]

Think here of the difference between geometry and physics. We really know in geometry - we cannot be in error about the Pythagorean theorem. But, in physics, we know only by keeping the 'real' facts out - by leaving out friction, the possibility that surfaces are not smooth, the chance that there will be a disturbance in the wind, or even the possibility that a comet will strike and disrupt the movements we are studying. In geometry, on the other hand, comet or no comet, the triangle always has three angles and the sum of the three angles of an equilateral trianle is always equal to two right angles. So, geometrical knowledge is real knowledge - there can be no error in it. You can think of Descartes' task - as you are reading his Meditations - in this way: he is trying to discover at least one geometrical truth about our everyday, experienced and sensed existence - at least one statement that we can know without the possibility of being deceived about it ever. On this basis - or foundation- Descartes thinks that he can build further statements of true knowledge. This means that Descartes is a RATIONALIST - his model of how to think about real life leads him to seek certain knowledge about it, as we do in geometry; and Descartes is also a FOUNDATIONALIST - he thinks of knowledge as a bulding whose solidity and stability require having sound and unshakable foundations - necessary and indubitable truths.

Theories of Truth

1. Correspondence Theories of Truth

According to Correspondence Theories of Truth, our perceptions are true only insofar as they correspond to something that is independently actual - independently from its being in our minds as an idea - and which serves as a guaranteee and standard of the truth of our perceptions and thoughts.

Think about this type of theory and you will realize two things: a. It is a commonsense view, in that we operate with it - even without realizing it, we assume that the ideas we form of things correspond to actual things out there, which give this specific meaning and content to the ideas in our minds. b. The theory is not as unassailable as it seems at first. The trick is this: The external, real, entities or standards that are so crucial to this theory CANNOT be tested. We must assume that they are there and that they can and do perform their important functions. We are acquainted with them only through the ideas of them we form in our minds. So, how can we possibly TEST them independently? We rather assume them to be serving this important role - of being the real things, by CORRESPONDENCE to which, our perceptions can be declared to be true.

2. Coherence Theories of Truth

Coherence Theories of Truth posit that what makes our perceptions and ideas in the mind true is that they form one coherent whole; in this case, we can cjeck, internally within our ideas, to see if any idea is not consistent with the rest or disrupts the overall coherence; then, this recalcitrant idea is to be declared false.

Although not as immeidately appealing to common sense, coherence theories might have a better chance of standing up to scrutiny in that they do not presuppose - as coherence theories do - an independent and prior acceptance of standards of truth.

3. Pragmatic Theories of Truth

An enticing famimly of theories is that of so-called Pragmatic Theories of Truth. According to such theories, ideas in my mind are true if the results from accepting those ideas as true are meaningful, efficacious, and consistent with ever-unfolding practical purposes that life presents to me all the time.

I suspect that most of you introduce assumptions from a pragmatic theory of truth when you make certain statements about truth. Notice, however, that this kind of theory is NOT as commonsense as the first category. It has a very obvious problem: What if something is FALSE BUT proves USEFUL? What if such a thing, moreover, remains useful down the line - maybe because it has helped bring about its own peculiar results. It is not implausible that we could live in a context of delusion and even illusions and yet have all our practical needs satisfied adequately. So, what kind of a theory of TRUTH can a pragmatic theory be?? Don't let its easy appeal mislead you.

How do we Know? – Sources of Knowledge -- Theories


Empiricism is the view that all knowledge we have originates from experience. Even novel notions we might conceive must have their origins in sense data, subsequently recombined in the brain to form strange forms. Obviously, if you are an empiricist, you don't give much credence to any notion about innate ideas - you don't buy into the notion that we are born with any knowledge that is prior to and independent of experience. In other words, you reject what is called a priori knowledge - an important concept which we will encounter again when we discuss Kant's monumental contribution to philosophy.


Descartes was a rationalist. Notice how Descartes is preoccupied with knowledge that is indubitable and incorrigible - cannot be doubted and cannot be further corrected or proven wrong by subsequent increments of knowledge. Indeed, technically speaking, this would not really be knowledge because, by definition, knowledge is what can never be proven wrong. [If proven wrong, I have to say that 'I thought I knew this but I was really wrong - I did NOT know it.' Descartes noticed that geometry deals with necessary truths - truths that cannot be doubted. Whether you are awake or asleep, 2+3=5; I mean that {II} and {III} put together give {II III}. If you dream that, suddenly, an extra element, a sixth element, appeared, this is odd and requires an explanation [did any of the five things split into two or what?] even in your dreams.]

Geometrical knowledge is what is accessible to the human mind, to reason - outside of the trappings of everyday experience. When we do geometry we are not dealing with experienced or natural objects. If this is your model of knowledge and you are looking for some way to account for ordinary knowledge problems in the same geometrical way, then you are a rationalist. This is what Descartes, who is a rationalist, does in his Meditations. He proceeds to find that one indubitable truth - "I think, therefore, I am" - which is a geometrical truth, isn't it? If x is asking questions, doubting, being duped, is uncertain, then x is [in the sense of exists.] You don't really need recourse to experience or your senses or ordinary everyday life to tell you that this is the case.Of course, this is related to life too, and this is why Descartes was satisfied that he scored a triumph when he hit upon this indubitable truth. Note that there is an underlying claim: That what is known to be as such - whether it is in geometry or in experience - IS of such a kind that it can be only known by reason. This is rationalism.

Review Suggestions:

How Can I Tell that I Am Awake? [Check the following criteria. Can you think objections and counter-examples to each of the following criteria?]

1. Dreaming: Less vivid impressions?

2. Dreaming: No pain! – would pinching oneself work?

3. Dreaming: Less detail?

4. Dreaming: Incoherent?

5. Being Awake: Capable of formulating and applying criteria?

6. Wondering about the question proves that I am awake?

7. Are there certain mental operations I cannot perform when asleep?

See what I said above, under discussion of rationalism. Even when asleep, 2+3=5. Do you agree? How do you understand this? Does this help Descartes? If this is the case, then, why can't we say that another test, to check if we are awake, is to try to perform a complex mental operation - for instance, to wirte a poem? What about trying to solve a mathematical problem? Would inability to solve the problem wake me up, or at least show to me that I am not awake? Probably not. Why, and how, is this different from the example from algebra [2+3=5 even in sleep]? The answer is this: 'I am able to perform this complex mental operation' show INDUBITABLY only that I am - I exist as in Descartes' example. It does not confirm that I am right - I might be deluding myself that I am able to perform this complex operation. Notice also that 'I am not able to perform this operation' also point to first-person certainty in Descartes' sense - it shows that I exist insofar as I am trying to perform this operation and failing.

Further Examples

Surgical Prodding of Brain Regions

“Brains in Vats”

Virtual Reality

Chuang Tzu’s Question [‘I slept and dreamed that I was a butterfly; then, I woke up; how do I know that I am not a butterfly dreaming that I am human?’ What is wrong with this question?]


You should know the meaning of this word by now. Descartes wanted to avoid skepticism - doubt that anything can be known with certainty. Descartes played the role of the skeptic not to reach skeptical conclusions but for the opposite reason: because he wanted a secure, solid foundation for knowledge; he thought that by doubting everything in a radical way, he could then reach that one statement; or a few statements, that cannot be doubted because they withstood the skeptical attack. Hume, who is associated with the Problem of Induction, which we will study next, contributed to skepticism by showing that the method of inference we use - and can only use - dealing with experience cannot possibly be shown to lead to certain knowledge.

Insistence on Reliability of Knowledge – ‘Knowing that I know.’

Why are these thinkers so serious about absolute certainty? Certainty is important, of course, but is the difference between 99.9% and 100% certainty that important? Perhaps the problem that agitates Descartes, and Hume, arises from these thinkers' foundationalism: They see knowledge as building from the foundation up. Without solid foundations, we cannot hope to have good knowledge. Inevitably, then, these thinkers are impressed by the impossibility of having 100% certainty [true knowledge] whenever experience and sensory data and time [unpredictability] and constant flux enter the picture. Perhaps foundationalism leads to skepticism and to efforts - like Descartes' - to combat it. But, notice: if you say that knowledge is to be assessed, for instance, only on the basis of its consequences - does what we think we know lead to useful results we can put to practice? - you are still holding to a philosophical theory of knowledge: the one we called above 'pragmatism.' Go back to the brief discussion of pragmatism above to see what kind of critique can be leveled at pragmatism.