Epistemology
Epistemology is the philosophical theory of knowledge.
It examines knowledge’s nature, sources, structure, limits, and justification.
The Greek roots episteme (knowledge) and logos (account) name an inquiry as old as philosophy itself.
Plato’s Theaetetus (c. 369 BCE) is the founding document of the field.
The classical analysis: justified true belief
The traditional analysis of knowledge, derived from a discussion in Plato’s Theaetetus at 201d, holds that S knows that p if and only if:
- p is true (truth condition)
- S believes that p (belief condition)
- S is justified in believing that p (justification condition)
This JTB analysis was the orthodoxy through 1963.
Each condition is well-motivated.
False beliefs are not knowledge.
Unbelieved truths are not known.
Lucky guesses, even if true and believed, do not constitute knowledge.
Gettier and its aftermath
Edmund Gettier’s three-page paper “Is Justified True Belief Knowledge?” (Analysis 1963) presented two counterexamples showing JTB is insufficient.
In the canonical case, Smith is justified in believing “Jones owns a Ford” (he has seen the registration).
Jones in fact does not own a Ford, but unknown to Smith, Brown is in Barcelona.
So “Jones owns a Ford or Brown is in Barcelona” is justified (by valid disjunction introduction), true (by the second disjunct), and believed.
But it is not knowledge.
Six decades of post-Gettier work have sought a fourth condition.
Defeasibility theory
Lehrer and Paxson’s “Knowledge: Undefeated Justified True Belief” (1969) requires that justification not be defeated by any true proposition the subject does not know.
Causal theory
Alvin Goldman’s “A Causal Theory of Knowing” (Journal of Philosophy 1967) requires that S knows p iff the fact that p is causally connected appropriately to S’s belief that p.
Reliabilism
Goldman’s “What Is Justified Belief?” (1979) introduced process reliabilism.
A belief is justified iff produced by a reliable cognitive process.
Process reliabilism shifts justification to the externalist register.
Tracking theory
Robert Nozick’s Philosophical Explanations (1981) defines knowledge with subjunctive conditionals.
S knows p iff (1) p is true, (2) S believes p, (3) if p were false, S would not believe p, (4) if p were true, S would believe p.
Subjunctive conditionals replace classical justification.
Virtue epistemology
Ernest Sosa’s A Virtue Epistemology (2007), Linda Zagzebski’s Virtues of the Mind (1996), and John Greco’s Achieving Knowledge (2010) treat knowledge as true belief produced by intellectual virtues or competences.
Sosa distinguishes animal knowledge (apt belief) from reflective knowledge (apt belief aptly noted).
The AAA framework — accuracy, adroitness, aptness — analyzes belief like archery: a shot is accurate if it hits the target, adroit if it manifests skill, apt if it hits because it manifests skill.
Knowledge first
Timothy Williamson’s Knowledge and Its Limits (2000) argued that knowledge is not reducible to or analyzable in terms of belief plus other components.
Knowledge is a primitive mental state with belief as a derivative concept.
This has had broad influence; many philosophers now reject the assumption that knowledge needs analysis.
The E=K thesis identifies a subject’s evidence with the propositions she knows.
Sources of knowledge
Traditional sources accepted by most epistemologists include perception, memory, testimony, introspection, and a priori reason.
Perception
Sense experience is the primary input source.
Direct realism (Reid, Gibson) holds that we perceive external objects immediately.
Indirect realism (Locke) holds that we perceive external objects via mental intermediaries.
Phenomenalism (Mill, Ayer) reduces external objects to actual and possible sense data.
Disjunctivism (McDowell, Snowdon) holds that veridical and hallucinatory experiences are fundamentally different mental states.
The contemporary debate is dominated by predictive-processing-inspired views.
Another central question is whether perception is theory-laden (Hanson 1958, Kuhn 1962, against Fodor’s “Observation Reconsidered” 1984).
Susanna Siegel’s The Contents of Visual Experience (2010) and The Rationality of Perception (2017) address cognitive penetration debates.
Memory
Apparent memories serve as evidence.
Preservationism holds that memory preserves prior justification.
Evidentialism holds that current evidence (including seemings of remembering) provides justification.
Testimony
Receiving information from others is a major source.
Reductionism holds that testimony is justified only by inductive support from past reliability (Hume).
Anti-reductionism holds that testimony is a basic source (Tyler Burge “Content Preservation” Philosophical Review 1993).
C. A. J. Coady’s Testimony: A Philosophical Study (1992) is the founding contemporary work.
Jennifer Lackey’s Learning from Words (2008) develops a hybrid view.
Introspection
First-person access to one’s own mental states was traditionally taken as infallible by Descartes.
Contemporary work argues introspection is highly unreliable.
Eric Schwitzgebel’s Perplexities of Consciousness (2011) catalogues introspective failures.
A priori reason
Knowledge independent of experience includes mathematics, logic, modal truths, and conceptual analyses.
Kant defended synthetic a priori knowledge.
Laurence BonJour’s In Defense of Pure Reason (1998) revived rationalism in analytic epistemology after Quine.
Intuition
Direct insight is important particularly in ethics and modal claims.
The role of intuition in philosophy is itself a contested topic in metaphilosophy.
Herman Cappelen’s Philosophy Without Intuitions (2012) challenges the standard story.
Timothy Williamson’s The Philosophy of Philosophy (2007) defends a deflationary account.
Skepticism
Skeptical arguments challenge whether knowledge is possible.
Pyrrhonian skepticism
Sextus Empiricus’s Outlines of Pyrrhonism (c. 200 CE) presents the ten modes and the five modes (Agrippan).
The Agrippan modes: disagreement, regress, relativity, hypothesis, circularity.
The aim is suspension of judgment (epoche) leading to tranquility (ataraxia).
Cartesian skepticism
Descartes’s evil demon (Meditation I 1641) and the dream argument introduce radical doubt.
Modern versions include the brain in a vat (Hilary Putnam, Reason, Truth and History 1981) and the Matrix scenario.
Humean inductive skepticism
Hume’s Enquiry (1748) Section IV holds that no non-circular justification of induction is possible.
The future may not resemble the past.
Wittgensteinian
Wittgenstein’s On Certainty (1969, posthumous) holds that some propositions are not subject to doubt because they structure the language game.
Responses to skepticism
Closure denial responds to skeptical arguments.
The closure principle states that if S knows p and S knows that p entails q, then S can know q.
Nozick (1981) denies closure to block skeptical arguments while preserving ordinary knowledge.
Contextualism (Keith DeRose, The Case for Contextualism 2009; Stewart Cohen; David Lewis “Elusive Knowledge” Australasian Journal of Philosophy 1996) holds that “knows” is context-sensitive.
Standards shift with conversational context.
In philosophy seminars, skeptical standards are high; in ordinary life, low.
Subject-sensitive invariantism (John Hawthorne Knowledge and Lotteries 2004, Jason Stanley Knowledge and Practical Interests 2005) holds that knowledge depends on the practical stakes the subject faces.
Mooreanism — G. E. Moore’s “Proof of an External World” (1939) — runs: “Here is one hand, and here is another; therefore there are at least two external things.”
This is the modus tollens of the skeptic.
Neo-Kantian transcendental arguments show that skepticism presupposes what it denies.
The new riddle of induction
Nelson Goodman’s Fact, Fiction, and Forecast (1955) introduced “grue.”
Grue applies to things examined before time t and found green, or not so examined and blue.
All emeralds examined so far are both green and grue.
Why do we project “green” rather than “grue”?
Goodman’s answer invokes entrenchment of predicates in our linguistic practice.
Structure of justification
How are beliefs justified?
Three main views on the regress of justification:
- Foundationalism — some beliefs (basic beliefs) are justified non-inferentially; others derive from these by inference.
- Classical (Cartesian) foundationalism requires infallible foundations.
- Modest foundationalism accepts fallible ones (Chisholm’s Theory of Knowledge 1966).
- Coherentism — beliefs are justified by their coherence with the whole web of beliefs; no foundations needed.
- Quine’s “Two Dogmas of Empiricism” (1951) and BonJour’s The Structure of Empirical Knowledge (1985, since renounced) defended coherentism.
- Infinitism (Peter Klein) — justification requires an infinite chain of non-repeating reasons.
- Foundherentism (Susan Haack, Evidence and Inquiry 1993) — a hybrid combining anchoring in experience with mutual support among beliefs.
Internalism vs externalism about justification
A foundational divide in contemporary epistemology.
Internalism
Internalism holds that what justifies a belief is something internal to the subject’s mental life, accessible by reflection.
Access internalism (BonJour, Chisholm) requires conscious access to justifying factors.
Mentalist internalism (Earl Conee and Richard Feldman, Evidentialism 2004) requires justifying factors to be mental states.
Externalism
Externalism holds that justification depends on factors external to the subject’s mental life.
Such factors include the reliability of the belief-forming process.
Goldman’s reliabilism, Plantinga’s proper function (Warrant and Proper Function 1993), and Sosa’s virtue reliabilism are externalist.
The new evil demon problem
Stewart Cohen’s “Justification and Truth” (Philosophical Studies 1984) challenges externalism.
A brain in a vat with our experiences would have beliefs formed by unreliable processes.
But it seems unfair to deny her justification.
Externalists respond with concepts like prima facie reasonableness.
Or they distinguish justification (externalist) from rationality (internalist).
Probability and Bayesian epistemology
Formal epistemology models belief as a credence — a degree of belief ranging over [0,1].
Bayesian epistemology imposes:
- Probabilism — credences satisfy the axioms of probability (Kolmogorov 1933).
- Conditionalization — upon learning E, replace prior P(H) with posterior P(H|E) by Bayes’s theorem.
Justifications include:
- Dutch book arguments (Ramsey “Truth and Probability” 1926, de Finetti 1937) — incoherent credences expose the agent to a guaranteed loss
- Cox’s theorem (R. T. Cox 1946) — derive probability axioms from minimal rationality desiderata
- Representation theorems — preferences satisfying axioms can be represented by expected utility maximization with probabilistic credences (Savage 1954)
- Accuracy-dominance arguments (Joyce 1998, Pettigrew Accuracy and the Laws of Credence 2016) — non-probabilistic credences are dominated in accuracy
Paradoxes
The lottery paradox (Henry Kyburg, Probability and the Logic of Rational Belief 1961) holds that for each ticket, it is rational to believe it will lose (probability 0.9999…).
Yet it is not rational to believe all will lose, contradicting closure under conjunction.
The preface paradox (David Makinson, “The Paradox of the Preface” Analysis 1965) holds that an author rationally believes each claim in her book.
But she also rationally believes some claim is mistaken (announced in the preface).
These motivate threshold (Lockean thesis, Foley Working Without a Net 1993) or context-sensitive (Hawthorne, Stanley) theories of how credences relate to outright belief.
Reflection principle
Bas van Fraassen’s “Belief and the Will” (1984) Reflection Principle holds that a rational agent’s current credences in p given that she will later have credence x in p should equal x.
This connects diachronic rationality with current credences.
Formal epistemology
Epistemic logic
Jaakko Hintikka’s Knowledge and Belief (1962) gave a possible-worlds semantics for “S knows that p” and “S believes that p” using modal logic.
S5 for knowledge implies positive introspection (Kp → KKp).
KD45 for belief is a typical choice.
Common knowledge
David Lewis’s Convention (1969) and Robert Aumann’s “Agreeing to Disagree” (Annals of Statistics 1976) developed common knowledge.
p is common knowledge among a group iff everyone knows p, everyone knows everyone knows p, and so on.
Common knowledge is central to game theory and coordination.
Dynamic epistemic logic
Public announcement logic (Plaza 1989, Gerbrandy and Groeneveld 1997) and dynamic epistemic logic (van Ditmarsch, van der Hoek, Kooi Dynamic Epistemic Logic 2007) model how knowledge updates with information.
Social epistemology
The shift from the lone Cartesian knower to the social context of knowledge has produced rich literature.
Testimony (social epistemology)
See Coady 1992, Lackey 2008, Goldman Knowledge in a Social World (1999), Faulkner Knowledge on Trust (2011) for the social-epistemic treatment.
Disagreement
David Christensen’s “Epistemology of Disagreement: The Good News” (Philosophical Review 2007), Adam Elga’s “Reflection and Disagreement” (Nous 2007), and Thomas Kelly’s “The Epistemic Significance of Disagreement” (2005) opened the field.
The conciliationist view holds that steadfast belief conflicts with peer status.
The steadfast view preserves one’s own assessment.
Expert testimony
When should non-experts defer to experts?
See Goldman’s “Experts: Which Ones Should You Trust?” (Philosophy and Phenomenological Research 2001).
Jury aggregation
Condorcet’s Jury Theorem (1785) shows that under certain conditions, majorities track truth.
Judgment aggregation paradoxes (List and Pettit Group Agency 2011) reveal the discursive dilemma.
Echo chambers
C. Thi Nguyen’s “Echo Chambers and Epistemic Bubbles” (Episteme 2020) distinguishes echo chambers (which discredit outside sources) from epistemic bubbles (which merely lack them).
Standpoint epistemology
Sandra Harding’s Whose Science? Whose Knowledge? (1991) and Patricia Hill Collins’s work hold that social location confers epistemic privilege on certain topics.
Pragmatism
The American pragmatist tradition includes Charles Sanders Peirce, William James, and John Dewey.
Peirce
Peirce’s “How to Make Our Ideas Clear” (Popular Science Monthly 1878) gave the pragmatic maxim.
The meaning of a concept is the practical consequences of its applicability.
Truth is what would be agreed in the long run by the community of inquirers.
James
James’s Pragmatism (1907) held that truth is what “works” — what guides successful action.
Dewey
Dewey’s Logic: The Theory of Inquiry (1938) held that knowledge is the outcome of inquiry — the warranted assertibility produced by intelligent practice.
Neo-pragmatism
Neo-pragmatism is associated with Richard Rorty (Philosophy and the Mirror of Nature 1979), Hilary Putnam, and Robert Brandom (Making It Explicit 1994).
Epistemology of science
Closely related to philosophy of science but with epistemic focus.
Falsificationism
Karl Popper’s Logik der Forschung (1934, English The Logic of Scientific Discovery 1959) holds that scientific theories cannot be verified, only falsified.
Demarcation proceeds by falsifiability.
Corroboration replaces confirmation.
Paradigm shifts
Thomas Kuhn’s The Structure of Scientific Revolutions (1962) describes normal science within a paradigm and periodic revolutions of paradigm shift.
Incommensurability between paradigms is a central thesis.
Research programmes
Imre Lakatos’s “Falsification and the Methodology of Scientific Research Programmes” (1970) describes a hard core protected by a belt of auxiliary hypotheses.
Programmes are progressive or degenerating based on whether their modifications generate confirmed novel predictions.
Epistemic anarchism
Paul Feyerabend’s Against Method (1975) holds that no methodological principle universally applies.
His slogan: “anything goes.”
Constructive empiricism
Bas van Fraassen’s The Scientific Image (1980) holds that we should accept theories as empirically adequate, not as true about unobservables.
Naturalized epistemology
Quine’s “Epistemology Naturalized” (1969) proposed that epistemology should become a chapter of psychology.
It should study how human cognition in fact produces beliefs from stimuli.
Critics charged a confusion of descriptive and normative.
Defenders argued normative principles can be informed by cognitive science.
Evolutionary epistemology
Donald Campbell’s “Evolutionary Epistemology” (1974) and Henry Plotkin’s Darwin Machines and the Nature of Knowledge (1994) treat knowledge as a biological adaptation.
Cognitive science of belief formation
Research on dual-process theories (Kahneman Thinking, Fast and Slow 2011), heuristics and biases (Tversky and Kahneman Science 1974), and Bayesian models of cognition (Tenenbaum, Griffiths) informs contemporary work.
Virtue epistemology
The virtue-theoretic turn (Sosa, Zagzebski, Greco, Roberts and Wood) shifts focus from belief-evaluation to person-evaluation.
Intellectual virtues include:
- Curiosity — appropriate desire for knowledge
- Open-mindedness — willingness to revise on evidence
- Intellectual humility — recognition of one’s epistemic limits
- Intellectual courage — willingness to defend unpopular positions
- Integrity — coherence of belief and action; sincerity
- Carefulness, attentiveness, diligence
Whitcomb, Battaly, Baehr, and Howard-Snyder address intellectual humility in The Limitations of the Open Mind (2014).
Alessandra Tanesini’s The Mismeasure of the Self (2021) gives a contemporary treatment of vices like arrogance and servility.
This connects epistemology to virtue ethics.
Some (Zagzebski) argue intellectual and moral virtues form a continuum.
Contemporary topics
Epistemology of perception
See Susanna Siegel’s work above on cognitive penetration.
Epistemology of modality
How do we know what is necessary or possible?
See Williamson’s The Philosophy of Philosophy (2007) ch. 5 and Chalmers’s “Does Conceivability Entail Possibility?” (2002).
Epistemic injustice
Miranda Fricker’s Epistemic Injustice: Power and the Ethics of Knowing (2007) distinguishes two forms.
Testimonial injustice involves deflated credibility due to prejudice.
Hermeneutical injustice involves inability to articulate experience for lack of concepts.
AI epistemology and LLM-generated content
Luciano Floridi’s The Ethics of Information (2013) and recent work address epistemic dependence on opaque systems.
Seth Lazar on algorithmic epistemology raises concerns about how LLMs reshape information ecosystems.
Bullshit, misinformation, and post-truth
Harry Frankfurt’s On Bullshit (2005) distinguishes bullshit from lying.
The bullshitter is indifferent to truth, while the liar engages with truth (by trying to conceal it).
Recent applied work addresses deepfakes and trust.
C. Thi Nguyen’s work on cognitive islands and trust is influential.
Regina Rini’s “Deepfakes and the Epistemic Backstop” (Philosophers’ Imprint 2020) treats video recording as an epistemic backstop now eroded.
Higher-order evidence
Higher-order evidence is evidence about your own reasoning.
Christensen, Kelly, and Lasonen-Aarnio have developed competing accounts of how to respond.
When you learn that your reasoning may have been impaired, should you revise the first-order conclusion?
Pragmatic encroachment
Pragmatic encroachment is the thesis that practical stakes affect whether one knows.
Stanley and Hawthorne defend it; others (Brown, Fantl and McGrath in different ways) elaborate or resist.
The bank cases (DeRose 1992) — whether one knows the bank is open Saturday when much or little hangs on it — are the standard motivating examples.
Epistemic norms of assertion
Williamson defends the knowledge norm: assert only what you know.
Weiner defends the truth norm; Lackey defends a reasonable-to-believe norm; others defend a justification norm.
The debate engages broader questions about the relation between knowledge, action, and assertion.