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From the "Routledge Encyclopedia of Philosophy"

CONCEPT OF KNOWLEDGE

The branch of philosophy concerned with the nature and extent of human knowledge is called epistemology (from the Greek episteme meaning knowledge, and logos meaning theory). Knowledge seems to come in many varieties: we know people, places and things; we know how to perform tasks; we know facts. Factual knowledge has been the central focus of epistemology.

We can know a fact only if we have a true belief about it. However, since only some true beliefs are knowledge (consider, for example, a lucky guess), the central question asked by epistemologists is 'What converts mere true belief into knowledge?'. There are many, and often conflicting, answers to this question. The primary traditional answer has been that our true beliefs must be based upon sufficiently good reasons in order to be certifiable as knowledge.

Foundationalists have held that the structure of reasons is such that our reasons ultimately rest upon basic reasons that have no further reasons supporting them. Coherentists have argued that there are no foundational reasons. Rather, they argue that our beliefs are mutually supporting. In addition to the constraints upon the overall structure of reasons, epistemologists have proposed various general principles governing reasons. For example, it seems that if my reasons are adequate to affirm some fact, those reasons should be adequate to eliminate other incompatible hypotheses. This initially plausible principle appears to lead directly to some deep puzzles and, perhaps, even to scepticism. Indeed, many of the principles that seem initially plausible lead to various unexpected and unwelcome conclusions.

Alternatives to the primary traditional answer to the central epistemic question have been developed, in part because of the supposed failures of traditional epistemology. These alternative views claim that it is something other than good reasons which distinguishes (mere) true beliefs from knowledge. Reliabilists claim that a true belief produced by a sufficiently reliable process is knowledge. Good reasoning is but one of the many ways in which beliefs can be reliably produced. The issue of whether the objections to traditional epistemology are valid or whether the proposed substitutes are better remains unresolved.

  1. The varieties of knowledge
  2. Propositional knowledge is not mere true belief
  3. Warrant
  4. Foundationalism and coherentism
  5. Defeasibility theories
  6. Externalism
  7. Epistemic principles
  8. The epistemic principles and scepticism
  9. The epistemic principles and some paradoxes
  10. Some challenges to traditional epistemology

1 The varieties of knowledge

Knowledge comes in many varieties. I can know how to adjust a carburettor. I can know a person. I can know that mixing bleach and ammonia is dangerous. In the first case, I possess a skill. In the second, I am acquainted with someone. In the third, I know a fact. Epistemologists have differed on the relationships between these types of knowledge. On the one hand, it could be held that knowing a person (place or thing), should be construed as nothing more (or less) than knowing certain facts about that someone and possessing the skill of being able to distinguish that person from other objects. On the other hand, it has been held that knowing facts depends upon being acquainted with particular objects. Whether the reduction of one form of knowledge to another is ultimately successful is an area of contention among epistemologists (see ACQUAINTANCE AND DESCRIPTION, KNOWLEDGE BY).

Nevertheless, it is knowledge of facts, so-called propositional knowledge, as opposed to knowledge by acquaintance or the possession of skills, that has been the central concern of epistemologists. The central question can be put this way: which beliefs of mine are to be counted as knowledge? This question presupposes that knowledge is a species of belief, but some might think that knowledge and belief are mutually exclusive: for example, we say such things as 'I do not believe that; I know it'. But we also say such things as 'I am not happy; I am ecstatic'. A suggested paraphrase of this expression seems to capture what is meant without denying the obviously true claim that ecstasy is a form of happiness. The paraphrase is: I am not merely happy, I am ecstatic . The parallel is: I do not merely believe it; I know it. Thus, this type of linguistic evidence does not support the suggestion that belief and knowledge are mutually exclusive. In general, epistemologists have held that propositional knowledge is a species of belief.

2 Propositional knowledge is not mere true belief

Propositional knowledge is a species of belief; but which beliefs are knowledge? The first thing to note is that a belief must be true in order for it to count as knowledge. But that is obviously not enough. First, true beliefs can be based upon faulty reasoning. Suppose that I believe that smoking is a leading cause of fatal lung cancer because I infer it from the fact that I know two smokers who died of lung cancer. The generalization is true, but my evidence is too meagre for my belief to count as knowledge. Second, true beliefs can be based on false beliefs. Modifying an example used by Bertrand Russell, suppose that I believe truly that the last name of the President of the United States in 1996 begins with a 'C'. Also suppose this belief is based upon the false belief that the President is Winston Churchill. My true belief that the President's name begins with a 'C' is not knowledge because it is based on a false belief.

Third, even some true beliefs resulting from good reasoning based upon true beliefs are not knowledge. Suppose that I believe (truly) that my neighbours are at home. My belief is based upon good reasoning from my true belief that I see lights on and that, in the past, the lights have been on only when they were at home. But suppose further that this time the lights were turned on by a guest and that my neighbours had just entered the house and would not have had time to turn on the lights. In this case, I fail to know that my neighbours are home. So, the central question becomes: what must be added to true belief to convert it into knowledge?

3 Warrant

The property, whatever it is, that, if added to true belief converts it into knowledge, we may refer to as 'warrant'. Knowledge, then, is true, warranted, belief. But simply to name the missing property does not bring us closer to understanding it and we must be careful not to think of 'warrant' as a sophisticated synonym for 'justified'. Let us say that a belief is justified just in case we are entitled to hold it on the basis of suitable reasons available to us. In the neighbour/lights case mentioned above, we have already seen that justification is not sufficient for warrant. Whether it is even necessary will be important in the discussion that follows, especially in §6.

Given the great variety of approaches to an account of warrant, is there any common, underlying starting point embraced by epistemologists? Yes: a warranted belief is one that is not held on the basis of mere cognitive luck. Plato appeals to that intuition in the Theaetetus; Aristotle's account of the transition from ignorance of the first principles in science to knowledge of them in the Posterior Analytics is designed to demonstrate that there are reliable cognitive mechanisms whose output is not the result of chance; Descartes (1641) proposes methods for acquiring beliefs that would necessarily lead to truth;suggests that Locke (1689) even if persons arrive at a true belief by accident, they are not thereby free from criticism.

Let us start with the assumption that a proposition is known just in case it is not an accident, from the cognitive point of view, that it is both believed and true. Hence the task becomes one of developing an account of warrant that accurately portrays what it is that makes a belief non-accidentally true from the cognitive point of view.

4 Foundationalism and coherentism

There are two main, traditional approaches to the account of justification: foundationalism and coherentism. Both are normative views about rules in virtue of which propositions ought to be accepted or ought to be rejected or ought to be suspended (see COHERENCE THEORY OF JUSTIFICATION AND KNOWLEDGE; FOUNDATIONALISM; NORMATIVE EPISTEMOLOGY). In order to characterize these approaches, recall how the ancient Pyrrhonian Sceptics divided the possible structures of reasons that provide a basis for accepting a belief (see EPISTEMOLOGY, HISTORY OF; PYRRHONISM). Suppose you hold a belief and offer another belief as the reason for the first – for example, suppose you believe that Ford cars are generally less expensive than BMWs. Your reason could be your belief that you were told so by a reliable person. An obvious question arises: what is your basis for believing that the person is reliable? You could answer with another reason and that reason could, itself, be supported by a further reason, and so on.

This process of providing reasons for your beliefs can have only three possible structures:

Foundationalism: The process of giving reasons could be such that not every reason is supported by another reason because there are basic reasons which have no need of further reasons supporting them.

Coherentism: The process of giving reasons could have no reason that is not supported by another reason, but there is not an infinite number of reasons. Thus, beliefs are mutually supporting.

Infinitism: The process of giving reasons could have no reason that is not supported by another reason, but there is an infinite number of reasons.

Foundationalism and coherentism have both been developed and defended, and there are well-known objections to each view. In contrast, the prima facie objections to infinitism have seemed so overwhelming that it has not been investigated carefully. Infinitism seems to require that a person should have an infinite number of beliefs (which seems on its face to be false). In addition, it seems to lead inevitably to the conclusion that no belief could ever be justified, since the process of justification would never come to an end.

The standard objections to foundationalism are several. First, as the Pyrrhonians would point out, there must be a distinction between what makes a belief properly basic and what makes it simply one for which no other reason is, in fact, given. Otherwise, the offered 'basic' reason is arbitrary. But if there is some further reason for thinking that an offered reason is not arbitrary, then there is a reason for accepting it, and the offered reason is, thereby, not basic. Hence, there can be no foundational propositions.

Second, some preferred candidates for properly basic reasons seem not to be properly basic on closer inspection. Consider perceptual judgments – the source of most of our knowledge of the external world according to many philosophers (see EMPIRICISM; A POSTERIORI). A reason for believing that there is a tree before me is that I see a tree before me. But the latter proposition does not appear to be properly basic because one could be required to explain what it is about what is seen that leads one to believe that it is a tree that one sees (as opposed to an illusion). Thus, some foundationalists have retreated to sensation-beliefs (so-called sense-data propositions) as their candidates for properly basic beliefs: for example, 'I seem to see a green, brown, tallish object' (see AYER, A.J.; BROAD, C.D.; MOORE, G.E.). But although these propositions might seem to be properly basic, there are notorious problems with the sense-data view (see PERCEPTION, EPISTEMIC ISSUES IN; SENSE DATA). First, the proffered basic beliefs seem to be too meagre to provide a sufficient basis for the rich scope of things we seem to know. For example, how can my knowledge that objects persist when not being perceived be traced to particular sense-data? Second, it appears that our knowledge of the way in which to characterize our sensations (private sensations accessible only to the individual having them) depends upon our knowledge of public objects (see CRITERIA; WITTGENSTEIN, L.). How could we know, for example, that we have a throbbing pain without first recognizing what it is for a public object (say, a muscle) to be throbbing?

Foundationalists have developed answers to these objections in part by liberalizing the requirements either for being properly basic or for being an acceptable pattern of inference from the foundational propositions to the non-foundational ones (see INFERENCE TO THE BEST EXPLANATION). For example, contextualist accounts of knowledge have been developed that hold that a proposition is properly basic just in case it is accepted by the relevant community of putative knowers. In a discussion with a friend I could offer as my reason for believing another moon of Jupiter had been discovered that 'I read it in the newspaper'. I would not need further reasons for believing that I read it. In contrast, at a convention of astronomers that reason would not be accepted. Hence, contextualists claim, what counts as a basic reason is context-dependent.

There are two obvious responses to contextualism. The first is that it might be an accurate description of some aspects of our epistemic practices, but the fundamental Pyrrhonian question remains: what distinguishes a properly basic proposition from one that is merely offered and accepted by a community of putative knowers? The issue concerns what beliefs, if any, ought to be offered and accepted without further reasons. The question is not what beliefs are offered and accepted without further reason. The second response is a corollary of the first. Knowledge seems to be a highly prized state of belief (as PLATO put it). But, if the contextualists were right, I would gain knowledge by joining a community of rather epistemically gullible and permissive folk. That hardly seems right! (see CONTEXTUALISM, EPISTEMOLOGICAL)

In sum, it remains a subject of dispute among epistemologists whether the stock of purported foundational propositions can be made sufficiently rich and abundant without including too many that clearly require evidential support, or whether the patterns of inferences can be liberalized sufficiently without allowing patterns that are not sufficiently truth-conducive.

The historical rival of foundationalism is coherentism. Coherentists deny that there are basic reasons and claim that all propositions derive their warrant, at least in part, from other propositions. The fundamental objection is this: Typically, we recognize that arguing in a circle is not an acceptable pattern of inference, so what makes it acceptable in some cases? Suppose I believe that apples contain vitamin C, at least in part because I believe that fruits contain vitamin C. I would surely be appropriately accused of circular reasoning if I believed, in part, that fruits contain vitamin C because apples do.

Coherentists would be quick to point out that they are not really suggesting that one should argue in a circle. Rather, they would point to the fact that our beliefs come in bunches with a web-like structure (see QUINE, W.V.O.). They are 'mutually supporting' just as the poles in a tepee are mutually supporting. A belief is warranted just in case it is a member of a set of coherent beliefs.

But whether these colourful analogies answer the basic objection is not clear. Presumably, circular reasoning is not acceptable because although it might be the case that if you believe b1 it might be reasonable to believe b2, and if you believe b2 it might be reasonable to also believe b1, their mutual support gives you no reason for believing them both. Thus, the fundamental question is this: What makes one total set of coherent beliefs, say T1, any more acceptable than an alternative total set of coherent beliefs, say T2?

The Pyrrhonian Sceptics would point out that coherentists either have an answer for that question or they do not. If they do, then they seem to have abandoned their central view, since there now seems to be a reason for adopting the set of beliefs, T1, that is not one of the beliefs in T1. Indeed, if they provide an answer, they have embraced foundationalism. If they do not have an answer, then it seems that adopting T1 is arbitrary. Coherentists have attempted to answer this objection by giving a 'meta-justification' for thinking that certain kinds of coherent belief systems are likely to contain true members. Indeed, some have argued that coherent beliefs are, by their very nature, likely to be true (see DAVIDSON, D.). But whether that strategy will suffice to answer the objections remains an open question in epistemology.

5 Defeasibility theories

A basic objection to the foundationalist's and coherentist's accounts of justification is that neither seems to be able to show that a true belief which satisfied their accounts would be non-accidentally true. First, as the neighbour/lights case showed, a true belief could be fully justified on their accounts, but not be knowledge. Second, as the Pyrrhonians pointed out, either the beliefs seem to rest upon arbitrary foundations or they seem to be only one of many, equally coherent sets of beliefs. The defeasibility theory was developed, in part, to address these issues. It holds, roughly, that it is not only the evidence that one possesses that makes a belief warranted; it is equally important that there is no defeating evidence that one does not possess. That is, in order for a belief to be warranted it must not only be justified (in the sense required by either the foundationalists or the coherentists) but its justification must be such that there is no truth which, if added to the reasons that justify the belief, is such that the belief would no longer be justified (see DEFEASIBILITY).

The defeasibility theory can explain why it is not a cognitive accident that the warranted belief is true. If any of the important supporting reasons (those that if removed would destroy the justification) were false, then adding the denial of those reasons (in other words, adding the truth) to one's beliefs would undermine the justification. In addition, if there is evidence that one does not possess such that it makes it an accident that the belief is true, the propositions describing that evidence would undercut the justification.

A well-known case will help to illustrate this (see GETTIER PROBLEMS). Suppose that I know Tom Grabit well and I see what appears to be Tom stealing a library book: I come to believe that Tom stole a library book. And, let us suppose that Tom did indeed steal the book. Foundationalists and coherentists could deploy their accounts in order to show that the belief is justified. Nevertheless, suppose that, unknown to me, Tom has an identical twin, John, who is a kleptomaniac and was in the library on the day in question and stole a copy of the same book. Even though I arrived at a true belief as a result of good reasoning based upon true propositions, I do not know that Tom stole the book since it is accidental, from the cognitive point of view, that I arrived at the truth. I could just as easily have based my belief on having seen John stealing the book.

The defeasibility theorists would point out that the belief that Tom stole the book is defeated; if the true proposition describing John were added to my beliefs, I would no longer be justified in believing Tom stole the book. In general, the defeasibility theory can rule out accidentally true beliefs as warranted because those beliefs would not be able to stand up to the truth.

Nevertheless, the defeasibility theory has its problems. The primary one is that it seems to exclude too much from what we know. Returning to the Grabit Case, suppose that everything is as it was except that Tom does not have a twin but that Tom's mother sincerely avows the claims about John. Now, there is a true proposition (Tom's mother has said sincerely that Tom has an identical twin, John) that defeats the original justification. Hence the belief that Tom stole the book would be defeated. But if Tom's mother were demented and there never was a twin, it seems that I knew all along that Tom stole the book.

Defeasibility theorists have tried to answer this objection by suggesting ways to distinguish between so-called misleading defeaters (for example, Mrs Grabit sincerely avows that Tom has an identical twin, John) and genuine ones (for example, Tom has an identical twin, John), but there is no agreement among epistemologists that any of these suggestions has succeeded in correctly capturing the distinction between genuine and misleading defeaters.

6 Externalism

Partly in response to the difficulties with foundationalism and coherentism even as supplemented by the defeasibility theory, epistemologists have developed a variety of alternative accounts of warrant. They have been called 'externalistic' because their accounts of warrant focus on features of the world other than the knower's reasons for belief. Two important ones are the causal theory and the reliabilist theory (see CAUSAL THEORY OF KNOWLEDGE; RELIABILISM).

In their purest forms, these accounts begin with the view that knowledge, and hence warrant, does not require justification. The foundationalists had already conceded that there are no reasons for properly basic beliefs. This seemed to create a problem for foundationalism only because it was assumed that all beliefs needed to be justified and the 'basic' reasons appeared to be arbitrary. But drop the requirement that beliefs need to be justified in order to be warranted, and this problem immediately disappears.

Roughly, the causal theory of warrant holds that a belief is warranted if and only if the state of affairs represented in the belief is appropriately causally related to the belief. For example, suppose I come to believe that there is a bird in a tree as a causal consequence of seeing the bird in the tree. Sometimes the causal connection is more complex; but this direct type of causal connection between the belief and what it represents will suffice for our purposes.

This theory is initially appealing because it appears to satisfy the basic requirement that a warranted belief be non-accidentally true since the state of affairs represented in the belief is a cause of my belief. However, it is easily seen to be both too weak and too strong; and there seem to be some deep problems with it as a general account of warrant. It is too weak because it would count some true beliefs as warranted that clearly are not known. Recall the Grabit case. My belief that I see Tom stealing the book is caused by Tom's stealing the book, but if he has an identical twin, I do not know that Tom stole the book. It is too strong because there seem to be many beliefs that count as knowledge which can not be appropriately causally related to what they represent. Suppose I know that there is no elephant smaller than a kitten: what possible causal connection could there be between there being no elephant smaller than a kitten and my belief? In addition, potential difficulties arise about knowledge of a priori propositions (such as 2 + 2 = 4) and counterfactuals (such as, if it were raining today, we would have called off the picnic). It looks as though there is no possible way to produce a causal connection between my belief and what is represented in the belief – at least as 'cause' is usually understood (see A PRIORI).

Nevertheless, a basic tenet of the causal theory might still be correct: Not all beliefs need to be based on reasons in order to count as knowledge. The reliabilist theory of warrant can be seen as the successor of the causal theory. Instead of requiring an appropriate causal connection between the states of affairs represented in the belief and the belief itself, a typical form of reliabilism holds that a belief is warranted just in case the process resulting in the belief produces true beliefs sufficiently often.

Thus, the non-accidental nature of the true belief receives a very straightforward analysis. The belief is non-accidentally true because the process that produces the belief produces true beliefs sufficiently often. This view has many advantages over the causal theory. My belief that elephants are larger than kittens need not be caused by that state of affairs. All that is required is that the process by which I come to believe that proposition typically (often enough) results in true beliefs. A priori or ethical propositions present no problem since there could be reliable processes that produce those beliefs.

Nevertheless, there are problems confronting this view. Suppose that you require that the process should produce true beliefs on 100 per cent of the occasions on which it arises. That is a very stringent condition; but it is not stringent enough! For if the belief that Tom Grabit stole a book arises only once in the history of the world – the time I saw him stealing the book – the actual process produced a true belief 100 per cent of the times it arose; but it is not knowledge. The obvious move for the reliabilist is not only to include the actual occasions when the particular belief is produced but rather to consider whether the type of process that produced this belief would produce true beliefs of this type sufficiently often. But correctly characterizing those types has not proved easy. Is the type of belief one in which Tom is involved? Or identical twins? Or libraries? That seems too narrow. Is the type of process one in which there is first a perception and then some inferences? That seems too broad. It remains an open question whether reliabilism can produce an acceptable account of the types of processes and the types of beliefs.

Finally, there is one further objection that some epistemologists have brought against reliabilism. Perhaps it is best illustrated in a case presented by Keith Lehrer (1990: 163) that can be summarized as follows: a certain Mr Truetemp has a thermometer-with-temperature-belief-generator implanted in his head so that within certain ranges of temperatures he has perfectly reliable temperature beliefs. When it is 50 degrees, he comes to believe that it is 50 degrees. When it is not 50 degrees, he does not come to believe that it is 50 degrees. He holds these beliefs without knowing why he does.

Such beliefs would satisfy all of the requirements suggested by the reliabilists, but many epistemologists would hold that although Mr Truetemp has true beliefs and they are not accidentally true because his thermometer-with-temperature-belief-generator is reliable, they are accidentally true from the cognitive point of view, as he has no reasons at all for his beliefs. Indeed, some would say that what Mr Truetemp possesses is a skill (of telling the temperature) and not propositional knowledge at all.

Here we can detect a fundamental clash of intuitions. The reliabilists would hold that Mr Truetemp does know; the traditional normativists would hold that he does not. There appears to be no way to satisfy both. But this much seems clear: There are some situations in which the steps in the process that brings about a belief include the holding of reasons. In those cases in which there is no automatic true-belief-generator (as in the Truetemp case) and in which we must rely upon our reasoning to arrive at a belief, the questions asked by the traditional normativists are crucial: what must the structure of our reasons be so as to make a true belief acceptable? Are there foundational reasons? Can mutually supporting reasons be offered without begging the question? (Could reasons be infinite in number?) And need those reasons be such that they are not undermined by the truth, as the defeasibility theorists would hold? At least in some cases, it seems that normative standards for belief-acquisition apply and their satisfaction will determine whether a belief ought to be accepted. Thus, it appears that an evaluation of the conditions under which beliefs ought to be accepted, denied or suspended is inescapable (see INTERNALISM AND EXTERNALISM IN EPISTEMOLOGY; JUSTIFICATION, EPISTEMIC).

7 Epistemic principles

Epistemic principles describe the normative epistemic status of propositions under varying conditions (see EPISTEMIC LOGIC). It is generally agreed that if a person, S, is justified in believing any proposition, x, then S is not at the same time justified in believing that not-x. Foundationalists and coherentists alike can, and typically do, accept this principle. Other principles are more controversial. They are intuitively plausible but they seem to provide a basis for scepticism and for some deep epistemic puzzles. Here are three of the more interesting principles.

Conjunction principle (CON-P): If S is justified in believing that x, and S is justified in believing that y, then S is justified in believing that (x and y).

Closure Principle (CLO-P): If S is justified in believing x, and x entails y, then S is justified in believing that y.

Evidence Transfer Principle (ET-P): If there is some evidence, e, that justifies S in believing that x, and x entails y, then e justifies S in believing that y.

In each principle and with suitable grammatical modifications 'justified' could be replaced by other epistemic terms, such as 'reasonable', 'plausible', 'evident', 'certain'. Furthermore, each principle is designed to capture a basis upon which a positive normative epistemic status of a proposition can be transferred to another proposition. As a corollary, 'S is justified in believing x' is not taken to entail 'S does believe that x, justifiably'. For S may not form the belief because of a failure to see the connection between the propositions. Finally, with regard to CLO-P and ET-P, since a tautology is entailed by every proposition, the entailment must be restricted to some form of relevant entailment and/or the range of propositions must be restricted to contingent ones (see RELEVANCE LOGIC AND ENTAILMENT). Other restrictions are no doubt necessary; but these three seemingly intuitive principles have been challenged at their core.

It is important to see some of the relationships between these principles. CLO-P does not entail CON-P since the CLO-P is about one proposition that S is justified in believing, not sets of propositions. In addition, CLO-P does not entail ET-P because CLO-P does not require that it is the very same evidence, e, that S has for x that justifies y for S. Thus, one can accept CLO-P without accepting either of the other principles.

8 The epistemic principles and scepticism

Scepticism – the view that we lack knowledge in those areas commonly thought to be within our ken – comes in many varieties. The most extreme view is global scepticism. It holds that we have very little, if any, knowledge. That view seems preposterous at first glance. Indeed, some epistemologists think that any theory that leads to global scepticism should, ipso facto, be rejected (see COMMONSENSISM; SCEPTICISM). Yet there are many arguments for global scepticism that are difficult to answer. In addition, more modest forms of scepticism about particular subject matters (for example, other minds or the future) have been developed. But since the more modest sceptics employ strategies similar to those employed by the global sceptics, I here consider only the most extreme form of scepticism – global scepticism (see OTHER MINDS).

We have already seen the basis for one such argument for global scepticism that can be gleaned from the Pyrrhonians, namely:

(1) All knowledge requires having reasons that are neither arbitrary nor question-begging nor infinitely many.

(2) The only structures for reasons are such that reasons are either arbitrary (foundationalism), question-begging (coherentism) or infinitely many (infinitism).

Therefore, there is no knowledge.

There are at least four possible responses to this argument: (1) the foundational, basic propositions are not arbitrary; (2) coherentism does not necessarily lead to question-begging arguments; (3) requiring infinitely many reasons for a belief does not entail that a belief cannot be justified; (4) not all knowledge entails having reasons. All but (3) have been systematically developed by epistemologists.

Pyrrhonism does not rely directly upon the epistemic principles discussed in the preceding section. But there are other important forms of scepticism that do. Consider this argument that can be traced to Descartes (see DESCARTES, R. §4):

(1) If I am justified in believing that there is a table before me, then I am justified in believing that I am not in one of the sceptical scenarios (evil demon worlds, for example) in which there is no table but it appears just as though there were one.

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(2) I am never justified in believing that I am not in one of the sceptical scenarios in which there is no table but it appears just as though there were one.

Therefore, I am never justified in believing that there is a table before me.

Premise 1 is a clear instance of CLO-P. Since the argument is valid (if the premises are true, the conclusion must be true), there are only three plausible responses: (1) CLO-P is false; (2) the second premise is false; (3) the argument begs the question. Responses (1) and (2) are relatively easy to envisage; the third is not so obvious. Roughly, the argument goes as follows: since one of the potentially available grounds for my being justified in believing that I am not in a sceptical scenario is any proposition that entails that I am not in such a scenario, every good argument for the second premise would have to establish that I am not justified in believing that there is a table before me. But that, of course, is the very conclusion.

It is important to note that there is an apparently similar argument for scepticism employing the stronger epistemic principle, ET-P:

(1) If the evidence, e, that I have for believing that there is a table before me is adequate to justify that belief, then it is adequate to justify the belief that I am not in one of the sceptical scenarios.

(2) The evidence, e, is not adequate to justify that I am not in one of the sceptical scenarios.

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Therefore, the evidence, e, is not adequate to justify that there is a table before me.

Of course, it is open to epistemologists to deny ET-P. Since one can deny ET-P without abandoning CLO-P (because CLO-P does not entail ET-P), that certainly seems to be a strategy worth considering. The discussion in the next section provides additional reasons for considering that strategy.

9 The epistemic principles and some paradoxes

There are many epistemic paradoxes (see PARADOXES, EPISTEMIC). I here consider two in order to show how they depend upon some of the epistemic principles considered earlier.

The Lottery Paradox: Suppose that enough tickets (say n tickets) have been sold in a fair lottery for you to be justified in believing that the one ticket you bought will not win. In fact, you are justified in believing about each ticket that it will not win. Thus, you are justified in believing the following individual propositions: t1 will not win. t2 will not win. t3 will not win.… tn will not win.

Now if the conjunction principle is correct, you can conjoin them, ending up with the obviously false but apparently justified proposition that no ticket will win. So, it seems that you are in the awkward position of being justified in believing each of a series of propositions individually, but not being justified in believing that they are all true. Some philosophers have thought that this seemingly awkward position is not so bad after all, since there is no outright contradiction among any of our beliefs as long as the conjunction principle is rejected. But others have thought that making it rational to hold, knowingly, a set of inconsistent beliefs is too high a price to pay.

Others have suggested that we are not actually justified in believing of any ticket that it will lose; rather what we are justified in believing is only that it is highly likely that it will lose. But the lottery can be made as large as one wants, so that any level of probability (below 1) is reached. Thus, this suggestion seems to rule out our being justified in believing any proposition with a probability of less than 1. That is a very high price to pay! There is no generally agreed-upon solution for handling the Lottery Paradox (see PROBABILITY THEORY AND EPISTEMOLOGY; CONFIRMATION THEORY).

The Grue Paradox: The so-called 'Grue Paradox' was developed by Nelson Goodman and has been recast in many ways (see GOODMAN, N.). Here is a way that emphasizes the role of ET-P:

All of the very many emeralds examined up to the present moment, tnow, have been green. In fact, one would think that since we have examined so many of them, we are justified in believing that (G): all emeralds are green. But consider another proposition, namely that all emeralds examined up to tnow are green, but otherwise they are blue. Let us use 'grue' to stand for the property of being examined and green up to tnow but otherwise blue. It appears that the evidence which justifies us in believing that all emeralds are green does not justify us in believing that (N): no emerald is grue.

What are we to make of this version of the paradox? First, note that it depends upon ET-P. Although (1) our inductive evidence (the many examined green emeralds) justifies (G), and although (2) (G) does entail (N), the inductive evidence does not justify (N). In other words, this version of the paradox arises because the evidence does not transfer as the principle would require. Second, note that CLO-P is not threatened by this paradox since it is the evidence for (G) that is inadequate for (N). (The issue is not whether we are justified in believing (N) whenever we are justified in believing that (G).)

But if ET-P were not valid, then the sting of this version of the paradox can be pulled. Recall the original Grabit case. In that case, I had adequate evidence for being justified in believing that Tom stole the book, that is, the person stealing the book looked just like Tom. It seems clear that this evidence is not adequate to justify the proposition that it was not Tom's identical twin who stole the book. If it were the twin, things would appear to be just as they did appear to be. But this tends to show that we do not typically impose ET-P on our evidence. There are other versions of the Grue Paradox that do not make explicit use of ET-P. For example, since 'all emeralds are green' and 'all emeralds are grue' are alternative hypotheses, it seems paradoxical that the very same evidence that justifies believing the first alternative also seems to support the second. But perhaps, like the version considered above, this apparent paradox rests on a mistaken intuition. Consider the Grabit Case once again. Here, the evidence which justifies the belief that Tom is the thief would also support the claim that Tom's identical twin stole the book. To generalize further, consider any hypothesis, say h, that is justified by some evidence that does not entail h. It is always possible to formulate an alternative hypothesis that is supported by that very evidence, namely (not-h, but it appears just as though h because of…). Thus, an intuitively plausible epistemic principle similar to ET-P might be invalid. That principle is: if there is some evidence, e, that justifies S in believing that x, and x is an alternative hypothesis to y, then e does not support y.

To sum up, if ET-P and similar epistemic principles do not accurately capture our normative epistemic practices and if the argument for scepticism that depends upon CLO-P begs the question, then the sting of Cartesian scepticism (considered in the previous section) is numbed and the Grue Paradox can be addressed. But those are big 'ifs', and the issue remains open (see INDUCTION, EPISTEMIC ISSUES).

10 Some challenges to traditional epistemology

A traditional question asked by epistemologists is 'what ought we to believe?' Typically, the answer is given by (1) describing the types of reasons that contribute to warranting a belief, and (2) developing a set of necessary and sufficient conditions for knowledge in which the types of reasons depicted in (1) play a prominent role. But there are many challenges to this answer.

We have already seen the challenge developed by the causal theorists and the reliabilists. Roughly, they hold that our beliefs need not be the result of proper reasoning to be counted as knowledge. Sufficiently reliable belief-acquisition methods are all that is required. Indeed, some have held that epistemology, when done correctly, is a branch of psychology because the primary issue is the study of reliable belief-acquisition methods. This programme has often been referred to as 'naturalized epistemology' and, in one form, its basic tenet is there are no a priori knowable epistemic principles (see NATURALIZED EPISTEMOLOGY; QUINE, W.V.O.).Another challenge to traditional epistemology comes from `virtue epistemology', which makes the primary object of epistemic evaluation traits of persons rather than properties of beliefs or belief-forming processes. The virture approach has been taken farthest by Linda Zagzebski (1996) who proposes an epistemic theory modelled on virtue ethics and argues that such a theory permits the recovering of such neglected epistemic values as understanding and wisdom (see VIRTUE EPISTEMOLOGY).

A further type of challenge is that of Edward Craig (1990). While allowing that the debate has been shaped by real features of the concept of knowledge, he rejects the project of analysing it in necessary and sufficient conditions. Instead, he tries to 'synthesize' the concept by deriving these features from a pragmatic hypothesis about its purpose, thus explaining the debate rather than joining it.

Even more radical challenges have been developed. First, some have argued that there is no unique method of acquiring and revising beliefs that ought to be employed by all people (see COGNITIVE PLURALISM). Second, it has been argued that the proposed conditions of good reasoning (for example, objectivity and neutrality) tacitly aim at something other than truth. They are developed to prolong entrenched power (see FEMINIST EPISTEMOLOGY). Finally, it has been argued that successful belief acquisition occurs when the future can be adequately anticipated and controlled (see PRAGMATISM).

The defenders of traditional epistemology have two basic types of reply. First, they can examine the particular arguments developed by the critics to determine whether any one of them is sound. Second, they can point out that the critics will have to defend the reasonableness of their views by at least tacitly employing the very principles of good reasoning investigated by traditional epistemologists. Of course, this would not show that the critic's position is false, but it does at least illustrate the universality of the question `what ought we to believe?'.

References and further reading

Alston, W. (1989) Epistemic Justification, Ithaca, NY: Cornell University Press. (Develops and defends a theory of knowledge containing elements of internalism and externalism.)

Annis, D. (1978) 'A contextualist theory of epistemic justification', American Philosophical Quarterly 15 (3): 213–19. (A non-technical contextualist account of justification.)

*Aristotle (3rd century BC) Posterior Analytics, ed. and trans. J. Barnes, Oxford: Clarendon Press, 1975. (Aristotle proposes and defends an empirical foundationalist account of knowledge. It can be viewed as containing a basis for a reliabilist account of knowledge of first principles in science.)

Armstrong, D. (1973) Belief, Truth and Knowledge, Cambridge: Cambridge University Press. (One of the first carefully developed reliabilist accounts of knowledge.)

Audi, R. (1993) The Structure of Justification, Cambridge: Cambridge University Press. (Develops and defends a version of foundationalism.)

Ayer, A.J. (1940) Foundations of Empirical Knowledge, London: Macmillan. (Develops and defends a foundationalist account of the structure of reasons.)

Bonjour, L. (1985) The Structure of Empirical Knowledge, Cambridge, MA: Harvard University Press. (Contains a sophisticated defence of coherentism.)

Broad, C.D. (1965) 'The Theory of Sensa' in R. Swartz (ed.) Perceiving, Sensing and Knowing, Berkeley, CA: University of California Press. (Develops the sense-data theory of knowledge. The collection contains many of the most important papers on perception written in the early- and mid-twentieth century.)

Chisholm, R. (1966) Theory of Knowledge, Englewood Cliffs, NJ: Prentice Hall, 2nd edn, 1977; 3rd edn, 1989. (The successive editions contain increasingly complex foundationalist accounts of knowledge along with versions of the defeasibility account.)

Code, L. (1991) What Can She Know? Feminist Theory and the Construction of Knowledge, Ithaca, NY: Cornell University Press. (Contains a sophisticated feminist challenge to traditional epistemology.)

*Craig, E. (1990) Knowledge and the State of Nature, Oxford: Oxford University Press. (The concept of knowledge approached by asking 'why do we have it?' Assumes some familiarity with the current debate. Mentioned in §10above.)

Davidson, D. (1983) 'A coherence theory of truth and knowledge', in E. LePore (ed.) Truth and Interpretation: Perspectives on the Philosophy of Donald Davidson, Oxford: Blackwell, 1986 . (Contains an account of the coherence theory of knowledge, as well as arguments for the claim that coherent beliefs must be true in the main.)

DeRose, K. (1995) 'Solving the Skeptical Problem', Philosophical Review 104 (January): 1–52. (Develops a contextualist theory of knowledge and uses it to address the problem of scepticism.)

*Descartes, R. (1641) Meditations on First Philosophy, in E. Haldane and G.R.T. Ross (eds) The Philosophical Works of Descartes, vol. 1, Mineola, NY: Dover Publications, 1955. (Contains a classic formulation of rationalistic foundationalism. Meditation I contains the 'Cartesian' argument for scepticism which he rejects in the following five meditations; Mediation IV employs the notion of warrant requiring non-accidentally true beliefs – see especially paragraphs 11–13 on page 176 of this edition.)

Dewey, J. (1929) The Quest for Certainty: Gifford Lectures 1929, New York: Capricorn, 1960. (Contains a contextualist account of doubt and justification.)

Dretske F. (1981) Knowledge and the Flow of Information, Cambridge, MA: MIT Press. (Contains a reliabilist account of knowledge employing information theory.)

Foley, R. (1987) A Theory of Epistemic Rationality, Cambridge, MA: Harvard University Press. (Develops and defends a sophisticated version of subjective justification.)

Gettier, E. (1963) 'Is justified true belief knowledge?', Analysis 23 (6): 121–3. (This article was responsible for focusing attention on the inadequacies of characterizing warrant in terms of justification alone.)

Goldman, A. (1967) 'A causal theory of knowing', Journal of Philosophy 64 (12) 357–72. (The first careful statement of the causal theory of warrant.)

—— (1986) Epistemology and Cognition, Cambridge, MA: Harvard University Press. (Contains a sophisticated development and defence of reliabilism.)

* Goodman, N. (1965) Fact, Fiction and Forecast, New York: Bobbs-Merrill, 2nd edn. (Contains the formulation of the Grue Paradox discussed in§9 above.)

Klein, P. (1981) Certainty: A Refutation of Scepticism, Minneapolis, MN: University of Minnesota Press. (Examines various forms of scepticism and develops the defeasibility theory of knowledge as a response to scepticism.)

—— (1996) 'Skepticism and closure: why the evil genius argument fails', Philosophical Topics 23 (1) spring 1995: 215–38. (Develops the 'question-begging' reply to scepticism briefly discussed in §8 above.)

*Lehrer, K. (1990) Theory of Knowledge, Boulder, CO: Westview Press. (An accessible introduction to the fundamental questions in epistemology that defends a version of coherentism and contains arguments against externalism including the TrueTemp example cited in §6 above; see especially pages 163–75.)

*Locke, J. (1689) An Essay Concerning Human Understanding, ed. A.C. Fraser, Mineola, New York: Dover Publications, 1959. (Contains the classic defence of empirical foundationalism conforming to the constraint that knowledge cannot be accidentally true belief. See especially Book XI, chapter 23, section 28 – pages 413–14 of this edition.)

Lucey, K. (1996) On Knowing and the Known, Buffalo, NY: Prometheus Books. (A comprehensive and accessible collection of essays on the concept of knowledge.)

Moore, G.E. (1953) Some Main Problems of Philosophy, New York: Collier Books, 1962. (The text of lectures given in 1910–11. See especially chapter 2 which develops the sense-data foundationalist theory of knowledge.)

Moser, P. (1989) Knowledge and Evidence, Cambridge: Cambridge University Press. (Contains a sophisticated development of foundationalism.)

Nozick, R. (1981) Philosophical Explanations, Cambridge, MA: Harvard University Press. (Develops and defends a reliabilist account of knowledge.)

Plantinga, A. (1993) Warrant: The Current Debate, Oxford: Oxford University Press. (A good source for discussions of various accounts of warrant.)

*Plato (4th century BC) Theaetetus, in The Collected Dialogues of Plato, ed. E. Hamilton and H. Cairns, Princeton, NJ: Princeton University Press, 1961. (Suggests that knowledge cannot be mere true belief even with a justification; but Plato does not suggest what the missing feature is.)

Pollock, J. (1986) Contemporary Theories of Knowledge, Totowa, NJ: Rowman & Littlefield. (Examines various contemporary accounts of knowledge and justification and develops a sophisticated version of the defeasibility theory.)

Prichard, H.A. (1950) Knowledge and Perception, Oxford: Clarendon Press. (Defends the view that knowledge is not a species of belief. See page 88 and following.)

Quine, W.V.O and Ullian, J. (1978) The Web of Belief, 2nd edn, New York: Random House. (A very accessible defence of coherentism.)

Radford, C. (1966) 'Knowledge – by examples' Analysis 27 (1): 1–11. (Defends the view that belief is not a necessary condition of knowledge.)

Sextus Empiricus (c.200) Outlines of Pyrrhonism, trans. R.G. Bury, Cambridge, MA: Harvard University Press and London: Heinemann, 1976. (See especially book I, chapter 15, for the argument that the three logically possible theories of justification lead to scepticism.)

Shope, R. (1983) The Analysis of Knowing, Princeton, NJ: Princeton University Press. (A thorough discussion of the Gettier Problem and the various approaches to solving it.)

Sosa, E. (1991) Knowledge in Perspective, Cambridge: Cambridge University Press. (Contains an interesting version of reliabilism that is designed to address issues generated by traditional normative epistemology.)

—— (ed.) (1994) Knowledge and Justification, vols 1 and 2, Brookfield, VT: Ashgate Publishing Company. (Contains a comprehensive set of essays on knowledge and justification.)

* Zagzebski, L. (1996) Virtues of the Mind, Cambridge: Cambridge University Press. (Contains a fully developed account of virture epistemology.)

PETER D. KLEIN

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