Concept

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.

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In full

Justified True Belief (JTB) is the classical analysis of knowledge, discussed by 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'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 treats truth as objective, revelation-grounded. The "T" in JTB is doing different work in each note.
• Faith and JTB. 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, Rationalism, Presuppositionalism, competing theories of what makes a belief justified.
• Foundationalism, the structural view that justification rests on basic beliefs.
• Revelation, divine self-disclosure proposed as a route to justification.