# Epistemology ## Intro *"How do you know what you know?"* Epistemology is the branch of philosophy that asks how knowledge works. The word comes from the Greek *epistēmē*, meaning "knowledge," and *logos*, meaning "study." The whole field is built around three durable questions. **What is knowledge?** When you say *"I know it is raining,"* what makes that different from *"I believe it is raining"* or *"I guess it is raining"*? Most philosophers since Plato have answered: knowledge is justified true belief. You have to believe it. It has to be true. And you have to have a good reason for believing it. All three. **Where does knowledge come from?** Senses? Reason? Memory? Testimony? Religious experience? Different schools of thought give different answers. Empiricists like John Locke and David Hume say all knowledge starts with sense experience. Rationalists like Descartes and Leibniz say some knowledge comes from pure reason alone. Reformed epistemology says some knowledge of God comes naturally to humans in a way that does not need to be argued for. **How is knowledge structured?** Are some beliefs foundational, like the floor of a building, with other beliefs built on top? Or do beliefs hold each other up like the strands of a spider web? Foundationalism takes the first view. Coherentism takes the second. These three questions are the master questions behind every other epistemological term you will see in the codex. [Empiricism](/codex/empiricism/), [Rationalism](/codex/rationalism/), [Foundationalism](/codex/foundationalism/), [Coherentism](/codex/coherentism/), [Reformed Epistemology](/codex/reformed-epistemology/), [Presuppositionalism](/codex/presuppositionalism/), and [Scientism](/codex/scientism/) are all answers to one or more of them. Why does this matter for Christian apologetics? Because most arguments about God are really arguments about epistemology underneath. *"I only believe what science can prove"* is an epistemological claim, not a scientific one. *"You can't know God exists, so the question is closed"* is an epistemological claim, not a theological one. *"Faith is believing what you have no reason to believe"* is an epistemological claim, and a wrong one (see [Faith](/codex/h0530-emunah/) for the actual definition). Apologists who can think clearly about epistemology can answer these moves at the level where they actually live. Apologists who cannot tend to argue around the surface and never reach the foundation. The page covers the three questions in depth, the major schools (Empiricism, Rationalism, Foundationalism, Coherentism, Reliabilism, Virtue Epistemology, Reformed Epistemology, Presuppositionalism), the major problems (the Gettier problem, the problem of the criterion, the regress problem), and the apologetic deployments that follow from each. ## In full **Epistemology** is the branch of philosophy concerned with the nature, sources, structure, and limits of knowledge. From the Greek *epistēmē* (knowledge) + *logos* (study), the discipline asks three durable questions: *What is knowledge?* (the analysis question), *How is knowledge obtained?* (the source question), and *How is knowledge justified?* (the structure question). It is the master discipline behind every other epistemic position in this codex, [Empiricism](/codex/empiricism/), [Rationalism](/codex/rationalism/), [Foundationalism](/codex/foundationalism/), [Coherentism](/codex/coherentism/), [Reformed Epistemology](/codex/reformed-epistemology/), [Presuppositionalism](/codex/presuppositionalism/), and [Scientism](/codex/scientism/) are all answers to one or more of these three questions. ## The three questions ### 1. What is knowledge? (The analysis question) The classical Western answer, traced to [Plato](/codex/plato/)'s *Theaetetus* (~369 BC), is **[Justified True Belief](/codex/justified-true-belief/)** (JTB): a person *S* knows a proposition *p* iff (i) *S* believes *p*, (ii) *p* is true, and (iii) *S* is justified in believing *p*. This analysis dominated Western epistemology for over two millennia. In 1963, [Edmund Gettier](/codex/edmund-gettier/)'s three-page paper *"Is Justified True Belief Knowledge?"* (*Analysis* 23) presented counterexamples in which a subject has a justified true belief that nonetheless fails to be knowledge, the truth-tracking is *accidental*. Post-Gettier epistemology has explored: - **No-defeaters** (Lehrer, Klein), JTB + no overriding defeating evidence. - **Causal theories** (Goldman, 1967), knowledge requires a causal connection between fact and belief. - **Reliabilism** (Goldman, 1979; *"What Is Justified Belief?"*), belief produced by a reliable cognitive process. - **Virtue epistemology** (Sosa, Zagzebski), knowledge is true belief produced by intellectual virtue. - **Proper-function / warrant** (Plantinga, *Warrant: The Current Debate* 1993), see [Reformed Epistemology](/codex/reformed-epistemology/). ### 2. How is knowledge obtained? (The source question) Major positions on the *source* of knowledge: - **[Empiricism](/codex/empiricism/)**, all knowledge derives from sense experience (Locke, Berkeley, Hume). - **[Rationalism](/codex/rationalism/)**, some knowledge is acquired through reason independently of experience (Plato, Descartes, [Leibniz](/codex/leibniz/)). - **Authority / testimony**, much knowledge comes through trustworthy sources (parents, experts, traditions). See Coady, *Testimony* (1992). - **Revelation**, divine self-disclosure as a source (Aquinas, *Summa Theologiae* I.1). - **Intuition / *a priori***, innate or self-evident knowledge (mathematical truths, basic moral judgments). - **Mystical / religious experience**, direct apprehension (Alston, *Perceiving God*, 1991). Most epistemologists today are *moderate*, they grant that some knowledge is empirical and some is *a priori*, while disputing the relative weight. ### 3. How is knowledge justified? (The structure question) Major positions on the *structure* of justification: - **[Foundationalism](/codex/foundationalism/)**, beliefs are justified by being either basic / properly basic or inferred from basic beliefs. - **[Coherentism](/codex/coherentism/)**, beliefs are justified by their coherence within a system, with no privileged foundation. - **Reliabilism**, beliefs are justified when produced by reliable cognitive processes. - **Virtue epistemology**, beliefs are justified when produced by intellectual virtues (open-mindedness, conscientiousness, etc.). - **Infinitism** (Klein), justification is an infinite chain of reasons, never terminating in foundations. ## Adjacent topics - **[Theories of Truth](/codex/theories-of-truth/)**, what *truth* is (correspondence, coherence, pragmatic, deflationary, constructivist). The "T" in JTB depends on which of these is operative. - **Skepticism**, global / Cartesian (am I dreaming?), local (induction, other minds), historical (Pyrrhonian). - **Levels of confidence**, certainty, probability, plausibility (see ). ## Christian engagement with epistemology Christianity has not endorsed a single epistemological theory but appears across the major schools: - **Thomistic** (Aquinas, *Summa Theologiae* I.84-86; *Summa Contra Gentiles* I), moderate empiricism + rational demonstration, *nihil in intellectu nisi prius in sensu* ("nothing in the intellect that was not first in the senses"); revelation supplements but does not contradict reason. - **Augustinian / illuminationist**, the mind is illuminated by divine light to grasp eternal truths ([Augustine](/codex/augustine/), *De Magistro*; *Confessions* X). Knowledge of necessary truths requires divine light. - **[Reformed Epistemology](/codex/reformed-epistemology/)** (Plantinga, Wolterstorff, Alston), belief in God can be properly basic; warrant comes from proper-function cognitive faculties (the *sensus divinitatis* + Holy Spirit's testimony). - **[Presuppositionalism](/codex/presuppositionalism/)** (Van Til, Bahnsen), the Christian worldview is the necessary precondition for the intelligibility of any knowledge ([Transcendental Argument for God](/codex/transcendental-argument-for-god/)). - **Classical / evidentialist** (Aquinas's heirs, Swinburne, Craig, Habermas), Christianity is rationally defensible by argument and evidence; faith is supported by, not opposed to, reason. These positions are not always mutually exclusive, Plantinga uses both natural-theological argument *and* properly-basic belief; the Thomist accepts revelation alongside reason. ## Key tensions and debates - **Internalism vs externalism**: must justifying conditions be cognitively accessible to the subject (internalism, Chisholm, BonJour) or can they be external facts about reliability / proper function (externalism, Goldman, Plantinga)? - **Strong evidentialism vs proper basicality**: Clifford's "*it is wrong always, everywhere, and for anyone, to believe anything upon insufficient evidence*" (*The Ethics of Belief*, 1877) vs Plantinga's properly-basic theistic belief. - **Naturalized epistemology** (Quine, *"Epistemology Naturalized,"* 1969), replace traditional epistemology with empirical psychology of belief-formation. Christian critics (Plantinga, *Warrant and Proper Function*) argue this collapses the normative question. ## Skepticism cluster (added 2026-05-01) The skeptical tradition is the perennial provocation that sets the agenda for any theory of knowledge. The codex gives it sustained treatment in a dedicated cluster: - [Skepticism](/codex/skepticism/), master hub mapping the varieties (Pyrrhonism / Academic / Cartesian / Humean / contemporary external-world / inductive / moral / religious / hyperbolic) and the major anti-skeptical strategies - [Pyrrhonism](/codex/pyrrhonism/), ancient skepticism: Pyrrho, Sextus Empiricus, *epoche*, *ataraxia*, the Ten and Five Modes (the Agrippan trilemma) - [Cartesian Skepticism](/codex/cartesian-skepticism/), modern external-world skepticism via skeptical hypotheses (dream / evil demon / brain in a vat); the closure-style argument that has shaped 20th- and 21st-c. analytic epistemology - [Mooreanism](/codex/mooreanism/), common-sense anti-skepticism; running the skeptical argument in reverse; "here is one hand" - [Closure Principle](/codex/closure-principle/), the closure premise of the Cartesian argument; Dretske / Nozick's closure denial as anti-skeptical strategy - [Epistemic Contextualism](/codex/epistemic-contextualism/), DeRose / Lewis / Cohen; "know" as context-sensitive - [Reformed Epistemology](/codex/reformed-epistemology/), Plantinga's properly-basic-belief response (related to Mooreanism) - [Presuppositionalism](/codex/presuppositionalism/), Van Til's transcendental anti-skepticism ## See also - [Justified True Belief](/codex/justified-true-belief/), the classical analysis - [Empiricism](/codex/empiricism/), [Rationalism](/codex/rationalism/), competing source theories - [Foundationalism](/codex/foundationalism/), [Coherentism](/codex/coherentism/), competing structure theories - [Reformed Epistemology](/codex/reformed-epistemology/), [Presuppositionalism](/codex/presuppositionalism/), Christian-philosophical schools - [Scientism](/codex/scientism/), overreaching empiricism - [Theories of Truth](/codex/theories-of-truth/), what the "T" in JTB is - [Self-refutation](/codex/self-refutation/), common test applied to epistemological positions - [Transcendental Argument for God](/codex/transcendental-argument-for-god/), presuppositionalist signature argument - [Skepticism](/codex/skepticism/), the perennial provocation - [Cartesian Skepticism](/codex/cartesian-skepticism/), [Pyrrhonism](/codex/pyrrhonism/), [Mooreanism](/codex/mooreanism/), [Closure Principle](/codex/closure-principle/), [Epistemic Contextualism](/codex/epistemic-contextualism/), the dedicated skepticism cluster - Plato, *Theaetetus*, the founding text - Edmund Gettier, 1963 counterexamples - [Alvin Plantinga](/codex/alvin-plantinga/), warrant and proper function - [Thomas Aquinas](/codex/thomas-aquinas/), moderate empiricism + revelation - [Rene Descartes](/codex/rene-descartes/), [David Hume](/codex/david-hume/), the modern skeptical interlocutors - Augustine, *Contra Academicos*; *si fallor sum* - Hubs Roadmap
## Common questions this page answers **Q: What is epistemology?** Epistemology is the branch of philosophy concerned with the nature, sources, structure, and limits of knowledge. It asks three durable questions: *What is knowledge?*, *How is knowledge obtained?*, and *How is knowledge justified?* Every other epistemic position, [Empiricism](/codex/empiricism/), [Rationalism](/codex/rationalism/), [Foundationalism](/codex/foundationalism/), [Coherentism](/codex/coherentism/), [Reformed Epistemology](/codex/reformed-epistemology/), [Presuppositionalism](/codex/presuppositionalism/), is an answer to one or more of these questions. **Q: What is the difference between knowledge and belief?** The classical Western answer, traced to [Plato](/codex/plato/)'s *Theaetetus*, is [Justified True Belief](/codex/justified-true-belief/): you know p if you believe p, p is true, and you are justified in believing p. Edmund Gettier's 1963 counterexamples showed JTB can be satisfied accidentally without genuine knowledge, opening contemporary work on no-defeaters, reliabilism, virtue epistemology, and Plantinga's proper-function/warrant account. **Q: Where does knowledge come from?** Different schools answer differently. [Empiricism](/codex/empiricism/) (Locke, Berkeley, Hume) says all knowledge derives from sense experience. [Rationalism](/codex/rationalism/) (Plato, [Descartes](/codex/rene-descartes/), [Leibniz](/codex/leibniz/)) says some knowledge comes from reason alone. Other proposed sources include testimony, intuition, revelation, and religious experience. Most contemporary epistemologists are moderate, granting that some knowledge is empirical and some *a priori*. **Q: Why does epistemology matter for apologetics?** Most arguments about God are really arguments about epistemology underneath. "I only believe what science can prove" is an epistemological claim, not a scientific one. "Faith is believing without evidence" is an epistemological claim, and a wrong one (see [Faith](/codex/h0530-emunah/)). Apologists who can think clearly about epistemology can engage these moves where they actually live, at the level of how knowledge works. **Q: How do Christians understand knowledge?** Christianity has not endorsed a single epistemology but appears across the major schools: Thomistic moderate empiricism plus rational demonstration; Augustinian illumination; [Reformed Epistemology](/codex/reformed-epistemology/) (Plantinga's properly-basic belief in God grounded in the *sensus divinitatis* and the Holy Spirit's testimony); [Presuppositionalism](/codex/presuppositionalism/) (the Christian worldview as precondition for any intelligibility); and classical evidentialism (Swinburne, Craig, Habermas). Most contemporary thoughtful apologists hold a hybrid. See [Christian Theories of Knowledge](/codex/christian-theories-of-knowledge/).