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Epistemology attempts to explain the nature and scope of knowledge and rational belief. Its purview also includes formulating and assessing arguments for skeptical conclusions that we do not have knowledge of various kinds. In addition, epistemologists address topics that are closely related to these core concerns, including evaluations of thought processes and the relationship of science to philosophy. What follows is an overview of contemporary developments in epistemology.

The Analysis of Knowledge

The traditional analysis of knowledge is that it is a combination of three conditions: truth, belief, and justification. The idea is that for someone to have factual knowledge, what is known has to be a fact and thus true; the person has to regard it as true, that is, believe it; and the person must have an adequate basis for believing itthat is, have sufficient justification for believing it. These conditions yield knowledge defined as a sufficiently justified true belief.

The publication by Edmund Gettier (1963) of one brief critical discussion of the traditional analysis brought about a flurry of activity in epistemology. Gettier refuted the traditional analysis by offering convincing counterexamples. He described examples in which someone forms a belief on the basis of strong justifying evidence, but the belief merely happens to be true as a result of a fortunate accident, independently of the evidence. Here is an example similar to Gettier's. Someone sees something that looks perfectly sheeplike in a nearby field. On that basis the person justifiably believes that there is a sheep in the field. As it turns out, what the person sees is not a sheep. It is a highly realistic statue. However, the person's belief that there is a sheep in the field is true because of the fortunate coincidence that there is a real sheep hidden from view elsewhere in the field. Such a belief is clearly not a case of knowledge despite its being an instance of justified true belief. So justified true belief is not sufficient for knowledge.

Arguing that the person in the example does not have an adequate basis for believing that there is a sheep in the field seems to require taking the general position that few beliefs are justified. For if that person does not have an adequate basis and is not justified, then someone in a similar situation who actually does see a sheep would also be unjustified, given that her visual information would be no better. In almost all cases of actual knowledge of the world, there are possible, although unusual, cases in which one has the same belief on the basis of comparable reasons, yet that belief is only true in this accidental way. Therefore, responding to the Gettier cases by raising the standards for justification leads to the conclusion that we know very little.

Most epistemologists responded to Gettier's examples by seeking a fourth condition for knowledge in addition to justified true belief. Some proposed that to have knowledge, it is also required that the justification for one's belief be undefeated, meaning roughly that there is no truth that would undermine the justification for the belief (Klein 1976). Others have suggested that in cases of knowledge the justification does not involve a falsehood (Chisholm 1989). Still others have required that the reasons justifying a known belief be conclusive roughly, reasons that would not exist unless the belief were true (Dretske 1971). Counterexamples refuted the original versions of these analyses, more complex analyses replaced the originals, and new counterexamples followed. (See Shope [1983] for a detailed summary of responses to Gettier's examples.)

Not all epistemologists accept the necessity of the three traditional conditions for knowledge. Some reject the justification condition. One proposed replacement requires a suitable causal connection between a known belief and the facts that make the belief true (Armstrong 1973, Goldman 1967). Another proposed replacement requires a known belief to vary counterfactually with the truth of that belief: if the belief were not true, it would not be believed by the same method, and if it were true, it would be believed by the same method (Nozick 1981). Others have taken the more drastic tack of denying that any set of necessary and sufficient conditions for knowledge can be given. An alternative explanation of knowledge is that it is the most inclusive factive mental state (Williamson 2000). A mental state is factive if the existence of the state guarantees its truth. Unlike the traditional analysis, this approach does not imply that the concept of knowledge can be decomposed into parts.

Although epistemologists have learned much about knowledge from this research, no consensus has emerged about the solution to the problem raised by examples like Gettier's.

Justification: Foundationalism and Coherentism

Justification itself has been investigated intensively in the wake of the Gettier problem. A central issue underlying views about justification is the infinite-regress problem. Typically, a belief is justified because it has support from other beliefs. For example, someone might be justified in believing that there are people in the next room by inference from the justified belief that Allen, Barbara, and Carol are in the next room. The supporting beliefs garner support from still other beliefs. The belief that Allen, Barbara, and Carol are in the next room might be justified by inference from the justified belief that they said they would enter the next room and then shouted that they had done so. However, given that our minds are finite, there cannot be an infinite regress of justifying beliefs. Therefore, either there are some beliefsbasic beliefsthat are justified without the support of other beliefs; or our beliefs form some sort of circle or web, with each justified/rational belief getting support from other beliefs within the system; or our beliefs are not justified at all. Foundationalism favors the first alternative, while coherentism favors the second. The third alternative, that no belief has any justification, seems indefensible.

The classic foundationalist view is that a belief is justified provided that it is a basic belief or rests upon a foundation of basic beliefs. Usually, the contents of basic beliefs are taken to be propositions about the mental states of the believer. For example, when someone observes an ordinary physical object in good viewing conditions, that person's visual system produces an experiential state. This is an internal mental state of the observer, knowable by introspection. Believing about oneself that one is in this experiential state is said to be a basic belief. Beliefs of this sort are supposed to provide a secure foundation for the rest of our justified beliefs. Classic foundationalists differ about the source of the security of basic beliefs. Candidate sources include the alleged infallibility of our introspective capacities and the alleged immunity from doubt of some beliefs. According to classic foundationalism, we acquire whatever justified beliefs we can get about the external world by inference from our introspectively justified beliefs about our own states. Some foundationalists hold that only a deductive (logically necessary) connection can secure sufficient justification for knowledge, whereas others hold that inductive or explanatory relations also suffice. The question of what support is sufficiently strong for knowledge is central to the discussion of epistemological skepticism.

Some foundationalists have relaxed the requirements for basic beliefs (Chisholm 1989, Huemer 2001). The central foundationalist view is that each justified belief is basic or derives its justification from basic beliefs. This view does not require basic beliefs to be certain or infallible. A more modest level of independent support is enough to stop the regress of derived justification. Foundationalists can consistently hold that support from other beliefs gets the basic beliefs beyond this modest level. If the basic beliefs need not be maximally secure, then another departure from the classic view becomes attractive. Basic beliefs can include ordinary perceptual beliefs. For example, the belief that one sees a dog can be basic. It can gain some justification that is independent of other beliefs directly from an experience, which is visually just as though one is seeing a dog. Modest foundationalism is widely thought to be an improvement upon classical foundationalism.

Modest foundationalism has its share of critics, however. Its defenders have been challenged to explain how the basic beliefs can receive even modest support from experience (BonJour 1985). The main problem is that the best understood sort of epistemic support is the justification that is given by the premises of a strong argument for its conclusion, yet the experiences cited by modest foundationalists as providing foundational support do not seem to qualify as premises of arguments. This is because experiences are not statements, but the only kinds of things that can be premises are statements.

Coherentism is the chief rival to foundationalism (Lehrer 1974, BonJour 1985). Coherentists deny that there are any basic beliefs. The secure foundations that classic foundationalists have sought are, according to coherentists, impossible. They contend that all justified beliefs get their justification from a relation of coherence that holds among a body of beliefs. Coherentists have attempted to say what constitutes coherence, often appealing to explanatory relations among beliefs as the source of coherence. Some propose that justification arises from reflective equilibrium a mutual adjustment of beliefs about particular cases and beliefs about general principles covering these cases that maximizes explanatory relationships among them (Goodman 1984).

Coherentists have been challenged to avoid the apparent implication of their theory that justified beliefs can have an implausible sort of detachment from sensory input. A body of beliefs can be internally coherent while the beliefs fail to take into account the person's experience, yet coherentism seems to imply that these cohering beliefs would be justified. Intuitively, however, such beliefs seem to be as unjustified as the beliefs formed by accepting as true everything in some well-crafted, elaborate, but fantastic story.

Not all philosophers agree that we must choose sides between foundationalism and coherentism. Several have argued that the central epistemological considerations on both sides can be reconciled (Alston 1989, Haack 1993, Sosa 1991).

Justification: Other Issues

In addition to formulating and assessing foundationalism, coherentism, and other theories of justification, epistemologists have addressed a variety of other questions about epistemic justification. Standard versions of foundationalism and coherentism share the presupposition that justification is determined by relations among the reflectively accessible contents of our mindsexperiential states, beliefs, memories, inferences, and so on. Some philosophers, however, have opposed this internalist presupposition, engendering extensive discussion of the contrast between this view about justification and its externalist alternatives. (See Kornblith 2001 for essays on these issues.)

For internalists, justification is determined entirely by internal mental factors, whereas externalists assert that justification is at least partly determined by other things. Some internalists also require the believer to be aware of all justifying factors. A typical internalist theory is evidentialism, which holds that evidence held in mind determines the epistemic status of beliefs (Conee and Feldman 2004, Haack 1993). Reliabilism exemplifies the externalist viewpoint (Goldman 1979). Reliabilism maintains that a belief's justification is determined by a propensity to produce true beliefs of the process or mechanism leading to the belief. This reliability is not an internal factor because the truth of a belief is usually not an internal fact.

A good example to point out the difference between an internalist theory and reliabilism involves the victim of a deceptive demon. The demon induces the victim to have the experiences like those a reasonable person might have through the perception of an ordinary environment. The demon's victim forms the same external world beliefs on the basis of these experiences. It is a further part of the example that the external world of the demon's victim is not at all an ordinary environment, and so her beliefs about her external world are not true. In such an example, the processes leading to the victim's external world beliefs seem to be unreliable because they produce her thoroughly false external world beliefs. So reliabilism seems to imply that such beliefs are not justified. The belief-forming processes of the counterpart person in a normal environment are presumed to be reliable, so that reliabilism implies that this person's beliefs are justified. In contrast, according to any internalist theory, the beliefs of both the normally situated person and the demon's victim are equally well justified if the individuals are in the same internal states.

Reliabilism has been a subject of intensive critical scrutiny since its introduction. Critics contend that reliabilists cannot plausibly specify the types of belief-forming processes or mechanisms on which the theory relies (Conee and Feldman 2004). For instance, the process of forming a typical visual belief can be classified as perception, visual perception, belief acquisition while relaxed, uninferred belief acquisition, and so on, indefinitely. The problem is to specify which of these process types has to be reliable in order for the resulting beliefs to be justified. Reliabilists must specify the relevant type for all of the processes that lead to justified beliefs. Critics have also charged that beliefs resulting from a reliable process can be unjustified when accompanied by a sufficient reason to think that the process is not reliable (BonJour 1985) and that beliefs resulting from an unreliable process can be justified when accompanied by reason to think that the process is reliable.

Some theories of justification require supplements to reliability. For instance, a proper functionalist theory holds that a belief is justified when the belief results from the operation of a generally reliable cognitive system that is functioning properly in an appropriate environment. One theistic variant of this view holds that the proper function of human cognitive systems is the result of the intentions of a creator (Plantinga 1993). In a nontheistic version, proper function is determined by natural selective forces. One prominent criticism of the proper functionalist approach is that it is possible for a cognitive mechanism to function improperly but felicitously. A perceptual mechanism might accidentally happen to work much better than it was designed to work. A resulting belief could be especially well justified by the acute perception.

Epistemologists also make comparisons between epistemic justification and ethical concepts such as obligation. Discussions of what a person is justified in believing easily slide into discussions of what the person should believe or is entitled to believe. Such talk is at least superficially similar to ethical evaluations of how a person should behave and what things the person is entitled to do. It can seem that the epistemic and ethical evaluations are fundamentally the same. However, there is some question about the applicability of ethical evaluations to beliefs. It is widely thought that what one morally should do is limited to those things that one can do. If something similar holds in epistemology, then what one should believe is limited to those things that one can believe. It apparently follows from this premise that beliefs must be under our voluntary control if we are to speak of our being justified in having them. Yet it seems that beliefs are not typically under voluntary control. Some philosophers respond by arguing that, contrary to appearances, we have sufficient control over our beliefs; some contend that it is acceptable to hold that we have justification for believing some propositions even though we are not able to control whether we believe them; and others conclude that few, if any, beliefs are justified since few, if any, are under our control. There is also concern about the connections between the epistemic justification of a belief and the moral or practical benefits of the belief. (Essays on this topic are collected in Steup 2001.)

Another widely discussed set of issues turns on a distinction between a priori justification and a posteriori justification. Justification of a belief is a priori when it does not derive from experience, and justification is a posteriori when it does. The leading candidates for a priori justification and knowledge are beliefs in basic truths of mathematics and logic. Other candidates include beliefs apparently made true entirely by conceptual relations, such as the belief that anything red is colored. These allegedly a priori justified propositions are, if true, necessarily true.

A priori justification seems mysterious to many philosophers, since it is difficult to understand what could justify beliefs independently of experience. A wide range of proposals has been made concerning how beliefs can have a priori justification. In the naturalistic approach a priori justification results from the operation of belief-forming processes that guarantee truth and justification (Kitcher 1980). The modal-reliability approach holds that conceptual intuitions necessarily present us with mostly truths (Bealer 2000). And a resolutely traditional approach holds that humans have a capacity for rational insight that finds truth-making, necessary connections in some thoughts (BonJour 1998).

It appears that a belief could not be a priori justified or known unless its truth is somehow abstractly guaranteed. It also appears that if there is an abstract guarantee that a belief is true, then the truth of the belief must not be merely contingent. So a priori knowledge of contingent truths would be surprising. Yet some philosophers have argued that we can have such knowledge (Kripke 1980), advancing the following kind of argument: Suppose that there is a unique tallest spy; knowing nothing about this and reasoning entirely in our armchairs, we can stipulate that the name "Stretch" refers to whoever happens to be the tallest spy, if there is one. Having done this, it seems that we can logically infer from what we have done, and thereby know a priori, the following contingent truth: if there is a unique tallest spy, then Stretch is a spy. Perhaps this knowledge would not be strictly a priori, since we would be using the experience of our introduction of the name "Stretch." Nonetheless, it seems to be a way to know a contingent truth that is at least remarkably similar to a priori knowledge.


Many traditional skeptical arguments appeal to the possibility of error. Skeptics often point out that it is possible for us to be wrong about even our most confident beliefs about the world external to our minds, perhaps because we are under the influence of a deceptive demon or some other source of deception. Skeptics typically make the further claim that this possibility implies that we lack knowledge of even the things about the world that we most confidently believe. (Many influential essays on skepticism may be found in DeRose 1999.)

Fallibilism is the heart of one influential response to skepticism (Chisholm 1989, Pryor 2000). Fallibilism is the view that knowledge is compatible with the possibility that the same belief on the same basis is false. For example, someone who has a clear view of a tree in the front yard and believes on a normal perceptual basis that there is a tree in the front yard is subject to some possibility of error. An experience that is visually just as though one is seeing a tree could have resulted from things like the efforts of a deceptive demon. However, a typical person who sees a tree has no reason at all to think that any such odd thing is actually occurring and every reason to think that there really is a tree present. Fallibilists hold that in such cases people often have sufficiently strong justification to know that there is a tree in the yard. According to fallibilists, a skeptical argument like the one about the possibility of error relies on setting the standard of justification for knowledge too high. We can have knowledge even though we cannot have the sort of absolute immunity from error that the skeptics wrongly associate with knowledge.

Fallibilism is not without problems. It is no easy task to explain what it is about our experiential evidence that makes it a good reason for thinking that we are in the presence of ordinary objects rather than the victims of some sort of deception. Some epistemologists contend that our justification for our external world beliefs depends upon an inference to the best explanation of our experiences (Vogel 1990), whereas others contend that there is something intrinsic to the character of experiences that makes them indicative of external world objects. Adequately spelling out just why our beliefs are even fallibly justified remains an unfulfilled task.

Some influential arguments for skepticism are updated versions of arguments based on possibilities of deception by dreams or demons. The newer arguments often appeal to the possibility of being a brain in a vat. The brain-in-a-vat arguments make use of the possibility that a fully functioning human brain, immersed in a life-sustaining vat of chemicals, receives computer-controlled neural stimulation that exactly matches the neural stimulation of an ordinary person in an ordinary environment. A premise of one brain-in-a-vat argument is that any of us might, for all we know, actually be such a brain in a vat. The argument also assumes that, since this possibility might be actual, we lack knowledge of the actual external world.

A much-discussed reply to such arguments employs a causal view of reference (Putnam). On one interpretation, the reply begins with the surprising contention that what a vat-entrapped brain would express by I am a brain in a vat would be a falsehood. A lifelong vat-entrapped brain would have learned the term vat from some computer-generated stimulations. The origin of the stimulation within the computer would have no causal connection to the brain's container of a sort that would be required for the brain's term vat to apply to the container. Hence, according to a causal view of reference, the brain's sentence I am a brain in a vat would not be true. Of course, what people in normal circumstances express by that same sentence is also false. Thus, the sentence I am a brain in a vat does not express a truth, whichever of these situations we are actually in. The antiskeptical reply concludes that by this use of a causal view of reference, we can justify denying the brain-in-a-vat argument's premise that, for all we know, we might be brains in a vat.

The success of this sort of antiskeptical reply is in dispute. In any event, a notable limitation of the approach is that at best it refutes skeptical arguments that rely on only some brain-in-a-vat possibilities. For instance, one possibility that is unaffected by the reply is that we recently became brains in a vat, and our term vat refers to the vat containing us because proper causal connections were forged in our pre-vat situation.

Skeptical arguments frequently rely on an epistemic-closure principle that says that if a person knows one proposition and sees that another proposition follows immediately from it, then the person knows the latter proposition, too. If someone knows an ordinary fact such as that she is seeing a table, then the closure principle implies that she could know by deduction that she is not a mere brain in a vat. Since, according to some skeptics, she cannot know that she is no brain in a vat, the skeptics conclude that she does not know anything from which she could deduce this, such as that she is seeing a table. Some philosophers have denied the closure principle in an effort to argue against this case for skepticism about knowledge of ordinary facts. Most philosophers, however, contend that some version of the closure principle must be true and any mistakes in skeptics' arguments must lie elsewhere (Hawthorne 2004).

Another response to skepticism appeals to epistemic contextualism (Cohen 1999, Lewis 1996). Contextualists endeavor to account for the intuitive pull of the arguments for skepticism while allowing that many of our ordinary attributions of knowledge are correct. Their central thesis is about truth conditions for uses of sentences including the word know and kindred terms. A statement of the truth conditions for a particular use of a sentence specifies the conditions that have to be realized in order for that use of the sentence to state a truth. The main form of epistemic contextualism holds that the truth conditions of particular uses of any sentence including know, or cognate expressions, vary with the context in which the sentence is used.

Typically, the varying aspect of the truth conditions is said to be the strength of the epistemic position that is required of the subject of the sentence for a use of know to apply to the subject. Usually, contextualists assert that the required strength of epistemic position varies across a range that allows, at its low end, many true sentences that attribute "knowledge" to someone. Thus, what we say is often true when, in ordinary circumstances, we classify as "knowledge" beliefs that are based on perception, memory, testimony, and perhaps inductive generalization and inference to the best explanation. Contextualists typically also assert that some contexts, at the high end of the range of variation, are demanding enough to make true denials of "knowledge" of the external world. For instance, contextualists often claim that where issues concerning skepticism are salient, the standards for true attributions of "knowledge" are very high and that consequently, in those contexts, skeptical denials of "knowledge" are correct.

Some critics of contextualism deny that skepticism is true even when arguments for it are salient. Appealing to antiskeptical grounds such as the fallibilism discussed above, the critics contend that the arguments fail and that skepticism is wrong whether or not we are thinking about it (Conee and Feldman 2004). Other critics question the linguistic foundations of contextualism (Stanley 2004).

Departures from Tradition

The philosophical study of knowledge, justification, and skepticism is the core of traditional epistemology. Some epistemologists have extended the discipline. One such extension involves connecting epistemology to scientific research about how people form beliefs and how they process information. Naturalism in epistemology is roughly the view that there is substantial overlap between epistemology and the sciences that study human cognition. Some philosophers endorse naturalism, whereas others find a reasonably clear distinction between the scientific/empirical questions about cognition and the conceptual questions at the heart of epistemology. A radically naturalistic epistemology advocates abandoning traditional epistemology and replacing it with the closest empirical discipline, cognitive psychology (Quine 1969). Few philosophers defend this extreme view. However, many urge close ties between epistemology and empirical studies of human cognition. For example, epistemologists who highlight the search for ways to improve our reasoning contend that the empirical study of how people actually reason is crucial for developing useful recommendations (Kornblith 1994). Philosophers who believe that the primary role of epistemology is to explain the concepts of knowledge, justification, and the like typically see less room for empirical input. Some advocate a less extreme form of naturalized epistemology that requires explaining central epistemic concepts in terms that they deem naturalistically legitimate.

Traditional epistemology has been largely individualistic in its emphasis on questions about knowledge and justification as they apply to individuals. However, a social epistemology has arisen that raises questions about what it is for groups to have knowledge and how social factors influence the spread and development of knowledge (Schmitt 1994, Goldman 1999).

Another approach in epistemology highlights epistemic virtues (Sosa 1991). One version of virtue epistemology is a variant on the reliabilist view discussed earlier. This approach attempts to characterize knowledge or justification in terms of epistemic virtues that yield reliably true beliefs, such as open-mindedness and a willingness to consider new evidence. In a greater departure from traditional issues, other versions of virtue epistemology propose that epistemologists replace or supplement the traditional topics with that of virtuous epistemic conduct.

Epistemology and Related Disciplines

There has been extensive and significant epistemological work done in relation to issues in the philosophy of mind. Externalism in the philosophy of mind, usually called content externalism, is the widely held view that environmental factors can help to determine the identity of some mental states. One simple content-externalist claim is that the content of a person's thoughts formulated with natural kind terms, such as elm and water, depends on causal connections to the kind that was actually involved in the person's learning the term. If the connection had been to a different natural kind, then the person's thoughts formulated with the same term would have included a concept referring instead to the other kind. There need not be any distinguishing feature that displays to the person which kind the person's thoughts are about.

Seemingly, if this simple content externalist theory is true, then we can know it a priori. We can know that external causes help to determine some thought contents by just considering how the reference of our natural-kind terms intuitively varies in some causally different hypothetical situations. If this is correct, then the theory appears to be incompatible with the conjunction of two plausible epistemological doctrines. One of the doctrines is that we can know the contents of our own thoughts by just giving introspective attention to them. If so, then we could combine our a priori knowledge of the simple content externalist theory with our introspective knowledge of the content of one of our thoughts that is expressible using water. We could infer that water is causally connected to the thought and that water therefore exists. Yet, according to a second plausible epistemological doctrine, knowledge of our environment is not so easy. It requires empirical information. Thus, the simple content externalist theory seems to imply that either we cannot know the contents of our thoughts as easily as it otherwise seems we can, or that empirical knowledge of the existence of things in our environment is easier than it otherwise seems to be.

Critics of this line of reasoning have asked whether it can really be known, without empirical investigation, that content externalism applies to any of our concepts. The applicability of the version of content externalism described here to a concept is contingent on the existence of an appropriate causal connection between the concept and some natural kind. This dependence suggests that empirical information about the existence of a properly connected kind is needed to justify applying content externalism to our concepts. (For further discussion, see the essays in Nuccetelli 2003.)

Much that qualifies as epistemology has been done in other areas of philosophy. What follows is a brief inventory of some epistemic work in allied fields. One classic epistemological topic is the problem of induction. This is the problem of establishing whether or not people can use observation of some cases to draw justified conclusions about unobserved cases, and if this can be done, explaining when and why such inferences are reasonable. This problem has been pursued within the part of philosophy of science known as confirmation theory. Second, factual knowledge entails truth. Truth is a traditional topic in epistemology. Various theories of truth are also presented and discussed in metaphysics, the philosophy of language, and philosophical logic. Third, rational change of belief is closely related to the epistemological topic of justified belief. Rational belief change is a focus of probability theory, especially under the classification of Baysian epistemology. Fourth, epistemological issues are often important to issues of morality and religion. Epistemic concerns pertaining to morality, such as the question of how we can know what is morally right, are usually discussed in works that are primarily about moral philosophy. Similarly, epistemic issues pertaining to God are discussed primarily in works in the philosophy of religion. Finally, in the vicinity of the border between epistemology and cognitive science there has been considerable attention devoted to the nature of purported sources of knowledge and to the ways in which they do their epistemic work. Topics here include perception, memory, intuition, and testimony.

See also A Priori and A Posteriori; Basic Statements; Classical Foundationalism; Coherentism; Contextualism; Doubt; Epistemology, History of; Evidentialism; Experience; Illusions; Inference to the Best Explanation; Internalism versus Externalism; Introspection; Intuition; Knowledge and Belief; Knowledge and Truth, The Value of; Knowledge, A Priori; Memory; Naturalized Epistemology; Perception; Propositional Knowledge, Definition of; Rationalism; Reason; Relevant Alternatives; Reliabilism; Self-Knowledge; Skepticism, History of; Social Epistemology; Solipsism; Subjectivist Epistemology; Testimony; Virtue Epistemology.


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Earl Conee (1996, 2005)

Richard Feldman (1996, 2005)

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  • Most online reference entries and articles do not have page numbers. Therefore, that information is unavailable for most content. However, the date of retrieval is often important. Refer to each style’s convention regarding the best way to format page numbers and retrieval dates.
  • In addition to the MLA, Chicago, and APA styles, your school, university, publication, or institution may have its own requirements for citations. Therefore, be sure to refer to those guidelines when editing your bibliography or works cited list.