# Justified True Belief ## Intro What does it mean to *know* something? Plato proposed an answer in the *Theaetetus* around 2,400 years ago, and most of Western philosophy went along with it for the next two thousand years. To know that some claim *p* is true, you need three things at once: You have to *believe* it. You cannot know something you do not believe; if you actively disbelieve global warming, you cannot also be said to know it. It has to actually *be true*. You cannot know a falsehood. If you confidently believe the earth is flat, that is not knowledge; it is delusion. You have to be *justified* in believing it. Random guessing does not count, even when you happen to be right. If you flip a coin to decide whether your bus will be on time and the coin says yes and the bus is on time, you did not *know* the bus would be on time; you got lucky. The combination is *justified true belief*, JTB for short. It was the textbook account of knowledge until 1963, when a short, three-page paper by a philosopher named Edmund Gettier blew it apart. Gettier showed cases where someone has a belief that is true, and is justified, but where we would not say they *know*, because the justification just happened to land on a true conclusion by accident. That sounds technical. The Gettier examples are the kind of puzzle philosophers have been arguing about ever since, and they matter because they force a more careful account of what *knowing* really requires. For Christian apologetics this matters in two directions. First, when someone says *"I don't know whether God exists,"* the right question back is, *what would count as knowing?* If they are demanding mathematical certainty, almost nothing about the real world counts as knowledge, including most of what they confidently believe. The honest standard for serious belief is something like *justified true belief* with the Gettier qualifications worked in, which is the same standard you would apply to history, science, or trust in another person. Second, the question of *how Christians know* God, through Scripture, through the Holy Spirit's witness, through reason, through experience, has been the subject of major work in Christian epistemology (Alvin Plantinga's *Warranted Christian Belief* is the landmark). Plantinga argues Christian belief is rationally appropriate even apart from the standard JTB framework, on something he calls *warrant*. The page below walks the JTB account, the Gettier counterexamples, the contemporary alternatives (reliabilism, virtue epistemology, Plantinga's proper-function account), and the application to religious knowledge. ## In full Justified True Belief (JTB) is the classical analysis of knowledge, discussed by [Plato](/codex/plato/) in the *Theaetetus* and dominant in Western epistemology, that holds a person knows a proposition *p* when three conditions are jointly met: the person believes *p*, *p* is true, and the belief is suitably justified. JTB sits at the head of ris3n's epistemology stream and is the framework against which later theological accounts of knowledge (revelation, proper basicality, self-authentication) are positioned. ## The three conditions 1. **Belief.** The knower must hold the proposition to be true. 2. **Truth.** The proposition must in fact be true. 3. **Justification.** The knower must have adequate grounds, reason, evidence, testimony, or some other warrant, for holding it. ## The Gettier problem [Edmund Gettier](/codex/edmund-gettier/)'s 1963 counterexamples show that JTB is *insufficient* for knowledge: a belief can be justified and true but only true by luck, in which case it falls short of genuine knowledge. The Gettier literature has driven epistemologists toward additional conditions (no-defeaters, reliable-process, virtue-theoretic, etc.) or toward abandoning the JTB framework entirely. ## Tensions - **Pragmatic vs objective truth.** *Ingredients in the Truth* absorbs pragmatic and constructivist framings into a unified picture, while the theological extension in [Belief Vs Knowledge](/codex/belief-vs-knowledge/) treats truth as objective, revelation-grounded. The "T" in JTB is doing different work in each note. - **Faith and JTB.** [Belief Vs Knowledge](/codex/belief-vs-knowledge/) argues theological faith satisfies JTB through revelation as justification. Whether revelation counts as "justification" in the same sense as empirical evidence is contested across traditions. ## See also - Plato, the *Theaetetus* origin. - Edmund Gettier, the canonical counterexample. - [Empiricism](/codex/empiricism/), [Rationalism](/codex/rationalism/), [Presuppositionalism](/codex/presuppositionalism/), competing theories of what makes a belief justified. - [Foundationalism](/codex/foundationalism/), the structural view that justification rests on basic beliefs. - [Revelation](/codex/revelation/), divine self-disclosure proposed as a route to justification.
## Common questions this page answers **Q: What is justified true belief?** The classical Platonic definition of knowledge: a person knows X if (1) they believe X, (2) X is true, and (3) they have justification for believing X. Without all three, you do not have knowledge. With all three, you have what philosophy called *episteme*. **Q: What is the Gettier problem?** In 1963, Edmund Gettier published a three-page paper showing cases where someone has a true, justified belief that we hesitate to call knowledge because the justification just happens to land on a true conclusion by accident. The cases forced philosophy to refine the JTB account. **Q: How does this apply to Christianity?** Christianity has classically held that faith is a form of knowledge with grounds (general revelation, special revelation, the inner witness of the Spirit), not blind belief. See [Belief Vs Knowledge](/codex/belief-vs-knowledge/) and [Reformed Epistemology](/codex/reformed-epistemology/) for the warrant-based account. **Q: What counts as justification?** Competing theories include foundationalism (some beliefs are basic, others are justified by them), coherentism (beliefs justify each other in a web), reliabilism (beliefs are justified when produced by reliable cognitive processes), and Plantinga's warrant account (proper function in the right environment). **Q: Is faith a kind of knowing?** Christianity has historically said yes. [Romans 1:18-21](/codex/romans-1-18-21/) says God's existence and power are *plain*. [Hebrews 11:1](/codex/hebrews-11-1/) uses Greek terms for substance and proof, not guesswork. Plantinga's [Reformed Epistemology](/codex/reformed-epistemology/) develops Christian belief as properly basic and warranted.