Epistemology: Theory of Knowledge, Justification, Foundationalism, and Coherentism

Epistemology (from the Greek epistēmē, “knowledge,” and logos, “account”) is the branch of philosophy that investigates the nature, sources, structure, and limits of knowledge. Its central questions look simple enough. What is it to know something? How do we know what we know? Can we be sure that we know anything at all? Yet each question unfolds into technical debates that have occupied philosophers from Plato to contemporary analytic work.

This article offers an overview of the field’s main problems and positions. Several topics already have dedicated treatments on this site and are only summarized here, with pointers to the relevant articles: the Gettier problem, skepticism, the a priori/a posteriori distinction, the cogito, the doxa/episteme contrast, and the theories of truth. For the general entry, see epistemology in the glossary.

1. What Is Knowing? The Tripartite Analysis

1.1 Plato: Meno and Theaetetus

Tradition often credits Plato with defining knowledge as justified true belief (JTB). The attribution is a simplification. In the Meno (97a–98a), Socrates argues that true opinion (alēthēs doxa) can guide action as well as knowledge, but it is unstable, like the statues of Daedalus that run away unless tied down; it becomes knowledge (epistēmē) when it is “tied down” by reasoning about the cause (aitias logismos). In the Theaetetus (201c–210a), the dialogue examines the proposal that knowledge is true opinion accompanied by a logos (“account,” “reason,” “definition”), considers three possible senses of logos, and ends in aporia without endorsing the definition. The relation between these passages and the doctrine of doxa and episteme is discussed in a separate article; the thinker is covered at Plato.

1.2 The Standard Definition

In twentieth-century analytic epistemology the definition became the conventional starting point: S knows that p if and only if (i) p is true, (ii) S believes that p, and (iii) S is justified in believing that p. The truth condition separates knowledge from mere conviction; the belief condition separates it from a truth the subject does not even accept; the justification condition separates it from a lucky guess. In 1963 Edmund Gettier showed that the three conditions together do not seem sufficient. The reactions (anti-luck conditions, causal theories, tracking, safety, virtue, knowledge-first) are detailed in the article on the Gettier problem and organize much of what follows.

1.3 Kinds of Knowledge

Philosophers traditionally distinguish propositional knowledge (knowing that), the main object of the field, from know-how (knowing how), tied to skills, and from knowledge by acquaintance, Bertrand Russell’s term for direct contact with objects, as opposed to knowledge by description. The intellectualist thesis that know-how reduces to propositional knowledge was defended by Jason Stanley and Timothy Williamson in “Knowing How” (2001) and remains disputed.

2. Sources of Knowledge

To ask about sources is to ask where beliefs that can amount to knowledge come from. The usual list includes:

• Perception: the most obvious source of empirical knowledge, but subject to illusion, hallucination, and the question of how experience can justify beliefs at all.
• Reason (rational intuition and reasoning): the source of mathematical and logical knowledge and, for rationalists, of metaphysical truths. Its relation to experience is the subject of the a priori/a posteriori distinction.
• Memory: preserves acquired knowledge; without it, reasoning and inference would be impossible, since they depend on retained premises.
• Introspection (awareness of one’s own mental states), whose authority was central for Descartes.
• Testimony: much of what we know (history, geography, science) depends on what others tell us. It returns in the section on social epistemology.

A separate question is whether these sources are generative or merely transmissive: memory and testimony, for instance, are generally seen as preserving or transmitting knowledge that already exists rather than producing it.

3. Rationalism and Empiricism

The modern debate about the origin of knowledge split into two families of doctrine. See also the glossary entries rationalism and empiricism.

Rationalism. For Descartes, Spinoza, and Leibniz, reason is a privileged source (for some, the principal one) of knowledge, and some truths are accessible independently of sensory experience. In the Meditations on First Philosophy (1641), Descartes seeks a point of indubitable certainty (the cogito) from which to rebuild knowledge. In the New Essays on Human Understanding (written c. 1704 and published posthumously in 1765), Leibniz answers Locke by defending virtually innate ideas and truths.

Empiricism. Locke (Essay Concerning Human Understanding, 1689), Berkeley, and Hume hold that the content of our ideas derives from experience. In Hume this thesis leads to skeptical conclusions about causation and induction, studied in this article.

Kant. In the Critique of Pure Reason (1781; 2nd ed. 1787), Kant proposes a mediation: all knowledge begins with experience, but not all of it derives from experience, because the subject contributes forms of sensibility (space and time) and categories of the understanding. Concepts without intuitions are empty; intuitions without concepts are blind. The price of the synthesis is the distinction between phenomena and things in themselves.

The opposition is partly a didactic simplification: Locke accepts intuitive and demonstrative knowledge; Descartes admits experience in physics. The debate survives, in other forms, in contemporary discussions of innateness, the a priori, and the status of intuition as evidence.

4. The Structure of Justification: Foundationalism, Coherentism, and Foundherentism

4.1 The Regress of Justification

If a belief is justified by another belief, and that one by yet another, what prevents an infinite regress? The problem goes back to Agrippa’s trilemma, transmitted by Sextus Empiricus in the Outlines of Pyrrhonism (I, 164–177): justification seems to lead to an infinite regress, a circle, or an arbitrary assumption (dogma). Each classical response corresponds to a way of accepting one of these branches: skepticism takes the trilemma as a reason to suspend judgment; foundationalism accepts a stopping point; coherentism accepts, in a sophisticated form, a circular or holistic pattern; infinitism (defended by Peter Klein) accepts the regress.

4.2 Foundationalism

For foundationalism, there are basic beliefs, justified without depending on other beliefs, which support the rest of the edifice. Descartes is the classical paradigm, with the cogito and clear and distinct ideas. Contemporary variants differ on what counts as a basic belief: classical foundationalism demands infallibility or incorrigibility (beliefs about the immediate content of consciousness); moderate versions accept fallible but prima facie justified perceptual beliefs, along the lines of authors such as Roderick Chisholm.

The main objection is Wilfrid Sellars’s attack on the “Myth of the Given” in “Empiricism and the Philosophy of Mind” (1956): if sense data justify beliefs, they must have propositional content and therefore already presuppose concepts and other beliefs; if they lack propositional content, they cannot justify. Responses try to show that experience can justify without itself being a belief.

4.3 Coherentism

For coherentism, justification does not flow from a base but from relations of coherence among beliefs: a coherent system supports each of its members. The associated image is Otto Neurath’s boat, rebuilt at sea plank by plank with no dry dock. Well-known defenders include Laurence BonJour (in The Structure of Empirical Knowledge, 1985, a position he later abandoned in favor of foundationalism) and Keith Lehrer. Donald Davidson formulated a coherence theory of truth and knowledge in “A Coherence Theory of Truth and Knowledge” (1983), arguing that belief is essentially veridical for the most part. On coherence as a theory of truth rather than justification, see the article on truth.

Two recurring objections: the isolation problem (a perfectly coherent system can be entirely detached from the world, like a well-constructed novel) and the charge of circularity.

4.4 Foundherentism (Susan Haack)

In Evidence and Inquiry: Towards Reconstruction in Epistemology (1993), Susan Haack proposes foundherentism, which seeks to combine what is acceptable in each position. Haack uses the analogy of a crossword puzzle: the clues correspond to experience (the “foundationalist” factor, since experiential evidence matters to justification without requiring basic beliefs immune to revision), and the mutual fit of intersecting entries corresponds to mutual support among beliefs (the “coherentist” factor). Justification comes in degrees and depends both on experiential evidence and on the integration of beliefs.

5. Internalism and Externalism

A second divide cuts across the first: must what makes a belief justified be accessible to the subject?

Internalism. The justifying factors are internal to the subject’s perspective, available by reflection. It is linked to the deontological idea that justifying is fulfilling epistemic duties (what one ought to believe, given the evidence). Internalism captures the intuition that two subjects with the same evidence and the same perspective should have the same epistemic status.

Externalism. Factors such as a causal relation to the world or the reliability of the belief-forming process can justify even if the subject lacks access to them. The most influential representative is Alvin Goldman: in “A Causal Theory of Knowing” (1967) he proposed a causal condition on knowledge, and in “What Is Justified Belief?” (1979) he defended process reliabilism: a belief is justified if it is produced by a reliable cognitive process, that is, one that tends to yield true beliefs. Later refinements appear in Epistemology and Cognition (1986).

Objections. Against reliabilism stands the new evil demon problem (associated with Keith Lehrer and Stewart Cohen, 1983): a subject systematically deceived by an evil demon but epistemically blameless seems justified even though her processes are unreliable. There is also BonJour’s (1980) case of Norman the clairvoyant, who reliably believes remote facts by a faculty for which he has no evidence and seems irrational in accepting them. And there is the generality problem: which type of process is the relevant one? Externalists reply by distinguishing justification (often tied, in their view, to reliability) from rationality or epistemic responsibility.

Mixed positions and the distinction between accessibilism and mentalism (justification supervenes on the subject’s mental states, whether or not these are accessible) complete the map.

6. Skepticism and Contextualism

Skepticism is the position that we lack knowledge, or justification, in some area of inquiry. From ancient Pyrrhonism (Pyrrho, Sextus Empiricus) to the Cartesian dream and evil-demon arguments in the Meditations (1641), skepticism works as a challenge that theories of knowledge must answer. See also Montaigne and the glossary entry skepticism.

In contemporary epistemology, skepticism is typically framed through the closure principle: if I know that p and know that p entails q, then I am in a position to know q. Given this, if I know that I have hands, I must know that I am not a brain in a vat (a scenario popularized by Hilary Putnam in Reason, Truth and History, 1981); since I cannot rule out the skeptical scenario, I do not know that I have hands.

The classic responses:

• Mooreanism. G. E. Moore, in “A Defence of Common Sense” (1925) and “Proof of an External World” (1939), holds that it is more certain that we have hands than that any skeptical premise is true, so the argument should be run in reverse. See G.E. Moore.
• Denying closure. Fred Dretske, in “Epistemic Operators” (1970), and Robert Nozick, in Philosophical Explanations (1981), reject the principle in certain cases.
• Contextualism. Stewart Cohen, Keith DeRose (for example, “Solving the Skeptical Problem,” 1995), and David Lewis (“Elusive Knowledge,” 1996) argue that the truth conditions of “S knows that p” vary with the context of the person attributing knowledge: in everyday contexts the standard is low and the attribution is true; in philosophical contexts, where skeptical possibilities become salient, the standard rises and the attribution becomes false. Skepticism would thus be correct in the skeptical context and harmless outside it. Criticisms include the claim that contextualism sidesteps rather than solves the problem, and the objection that the semantics of “knows” would be unusually unstable. Alternatives include subject-sensitive invariantism (John Hawthorne, Jason Stanley), on which what varies is the subject’s practical stakes, not the attributor’s context.
• Wittgenstein. In On Certainty (published posthumously in 1969), Wittgenstein suggests that certain propositions function as “hinges” that are not objects of doubt or justification because they underpin the practice of doubting and justifying.

7. Virtue Epistemology

Virtue epistemology shifts the focus from the isolated belief to the faculties and traits of the cognitive agent, by analogy with virtue ethics. There are two main strands.

Virtue reliabilism. Ernest Sosa, beginning with “The Raft and the Pyramid” (1980) and the essays collected in Knowledge in Perspective (1991), holds that knowledge is true belief that manifests a competence (intellectual virtue) of the subject. In A Virtue Epistemology (2007) he distinguishes animal knowledge (apt belief, true because of competence, without a reflective perspective) from reflective knowledge (in which the subject also assesses the aptness of her own belief). On this view, belief is a performance that can be evaluated as accurate, adroit, and apt.

Virtue responsibilism. Linda Zagzebski, in Virtues of the Mind (1996), takes the character virtues of Aristotelian ethics as her model: open-mindedness, intellectual courage, intellectual humility, honesty. She defines knowledge as a state of cognitive contact with reality arising from acts of intellectual virtue. In “The Inescapability of Gettier Problems” (1994) she argued that any theory that keeps justification logically independent of truth is open to Gettier-type cases, and used this to motivate a virtue-based account. Cf. the Gettier article.

Both strands share an interest in the value of knowledge: why should knowledge be more valuable than mere true belief? The problem goes back to the Meno and is one of the engines of virtue epistemology.

8. Naturalized Epistemology

In “Epistemology Naturalized” (1969), W. V. O. Quine proposes abandoning the Cartesian project of a “first philosophy” that would justify scientific knowledge from foundations prior to it. With the failure of the program of reducing statements about the world to sense-data terms (the project of Carnap in the Aufbau, 1928), Quine suggests that epistemology should become a chapter of empirical psychology: the study of how human beings actually move from sensory stimulation to theories about the world. Human knowledge is seen as a whole in which no statement is immune from revision, a thesis associated with the holism of “Two Dogmas of Empiricism” (1951).

The main objection, pressed by Jaegwon Kim (1988), is that abandoning normative justification removes what was distinctive about epistemology: without norms there would be no difference between well-grounded and ill-grounded belief. In later writings Quine replied that normativity remains as a technology of the pursuit of truth, internal to science. The relation of the project to the philosophy of science is treated in another article; pragmatism is another root of epistemological naturalism (pragmatism).

The legacy of naturalism includes Goldman’s reliabilism and experimental epistemology, which empirically tests intuitions about cases of knowledge, including Gettier cases, with results suggesting variation across cultures and groups, findings that are still debated.

9. Social Epistemology and Testimony

Traditional epistemology treated the knower as an isolated individual. Social epistemology starts from the observation that knowledge is, to a large extent, acquired, distributed, and evaluated socially.

Testimony. Can testimony be a basic source of justification? For reductionism, associated with Hume (Enquiry Concerning Human Understanding, section X), trust in testimony must itself be justified by independent evidence that informants are generally reliable. For anti-reductionism, inspired by Thomas Reid (Inquiry into the Human Mind, 1764), we have a natural disposition to accept what we are told, and this is prima facie justified absent defeaters. C. A. J. Coady’s Testimony (1992) is a landmark defense of anti-reductionism.

Goldman’s social epistemology. In Knowledge in a Social World (1999), Alvin Goldman assesses social practices (communication, institutions, media, law) by their effects on the truth of beliefs, a “veritistic” approach.

Peer disagreement. If someone as informed and intelligent as I am disagrees with me, should I revise my belief? Answers range from “conciliationism” (lower one’s confidence) to the view that one may keep the original belief under certain conditions.

Epistemic injustice. Miranda Fricker, in Epistemic Injustice: Power and the Ethics of Knowing (2007), identifies testimonial injustice (reduced credibility due to identity prejudice) and hermeneutical injustice (a gap in shared interpretive resources that makes a social experience unintelligible), tying epistemology to ethics and politics. The discussion converses with the critical tradition on knowledge and power, for example in Foucault.

10. Assessment

The overview shows that epistemology offers no consensus on the analysis of knowledge. In summary:

What these positions share is the recognition that knowledge is a cognitive good involving truth, and that the question of what makes it possible and legitimate cannot be separated from questions about mind, language, and society. For further reading on this site, see the articles on truth, logic, and the philosophy of language.

References

• Plato, Meno (97a–98a); Theaetetus (201c–210a).
• Sextus Empiricus, Outlines of Pyrrhonism, I, 164–177 (modes of Agrippa).
• René Descartes, Meditations on First Philosophy (1641).
• John Locke, An Essay Concerning Human Understanding (1689).
• Gottfried W. Leibniz, New Essays on Human Understanding (written c. 1704; published 1765).
• Immanuel Kant, Critique of Pure Reason (1781; 2nd ed. 1787).
• Edmund Gettier, “Is Justified True Belief Knowledge?”, Analysis 23, 1963, pp. 121–123.
• Alvin Goldman, “A Causal Theory of Knowing,” Journal of Philosophy, 1967; “What Is Justified Belief?”, 1979; Epistemology and Cognition (1986); Knowledge in a Social World (1999).
• Wilfrid Sellars, “Empiricism and the Philosophy of Mind” (1956).
• W. V. O. Quine, “Epistemology Naturalized,” in Ontological Relativity and Other Essays (1969).
• Susan Haack, Evidence and Inquiry: Towards Reconstruction in Epistemology (1993).
• Laurence BonJour, The Structure of Empirical Knowledge (1985).
• Ernest Sosa, Knowledge in Perspective (1991); A Virtue Epistemology (2007).
• Linda Zagzebski, Virtues of the Mind (1996).
• David Lewis, “Elusive Knowledge,” Australasian Journal of Philosophy, 1996.
• Keith DeRose, “Solving the Skeptical Problem,” Philosophical Review, 1995.
• Timothy Williamson, Knowledge and its Limits (2000).
• C. A. J. Coady, Testimony: A Philosophical Study (1992).
• Miranda Fricker, Epistemic Injustice: Power and the Ethics of Knowing (2007).
• Stanford Encyclopedia of Philosophy, entries “Epistemology” and “Virtue Epistemology.”

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