Concept

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, Rationalism, Foundationalism, Coherentism, Reformed Epistemology, Presuppositionalism, and 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 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, Rationalism, Foundationalism, Coherentism, Reformed Epistemology, Presuppositionalism, and 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's Theaetetus (~369 BC), is 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'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.

2. How is knowledge obtained? (The source question)

Major positions on the source of knowledge:

Empiricism, all knowledge derives from sense experience (Locke, Berkeley, Hume).
Rationalism, some knowledge is acquired through reason independently of experience (Plato, Descartes, 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, beliefs are justified by being either basic / properly basic or inferred from basic beliefs.
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, 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, De Magistro; Confessions X). Knowledge of necessary truths requires divine light.
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 (Van Til, Bahnsen), the Christian worldview is the necessary precondition for the intelligibility of any knowledge (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, master hub mapping the varieties (Pyrrhonism / Academic / Cartesian / Humean / contemporary external-world / inductive / moral / religious / hyperbolic) and the major anti-skeptical strategies
Pyrrhonism, ancient skepticism: Pyrrho, Sextus Empiricus, epoche, ataraxia, the Ten and Five Modes (the Agrippan trilemma)
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, common-sense anti-skepticism; running the skeptical argument in reverse; "here is one hand"
Closure Principle, the closure premise of the Cartesian argument; Dretske / Nozick's closure denial as anti-skeptical strategy
Epistemic Contextualism, DeRose / Lewis / Cohen; "know" as context-sensitive
Reformed Epistemology, Plantinga's properly-basic-belief response (related to Mooreanism)
Presuppositionalism, Van Til's transcendental anti-skepticism