The theory of knowledge: JTB and Gettier: QCE Philosophy and Reason
“Explain and evaluate the justified true belief analysis of knowledge and the Gettier problem, including proposed responses”
Epistemology asks what knowledge is, beyond mere true belief. The classical justified true belief analysis says S knows that p if p is true, S believes p, and S is justified in believing p, with justification meant to exclude lucky guesses. Gettier's 1963 cases show JTB is not sufficient: a belief can satisfy all three conditions yet be true only by luck, as when Smith's justified inference turns out true by coincidence, so it is not knowledge. Proposed repairs add a fourth condition: no false lemmas, a reliable belief-forming process (reliabilism), no defeaters (defeasibility), or a causal, safety or sensitivity link. Each excludes some epistemic luck, but none is universally accepted.
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What this dot point is asking
QCAA wants you to examine the central question of epistemology (the theory of knowledge): what is knowledge? You need the classical justified true belief (JTB) analysis, the famous Gettier problem that appears to refute it, and the main attempts to repair the analysis. This is foundational for the scepticism and rationalism-empiricism topics.
The answer
Knowledge versus belief
Not every true belief is knowledge. A lucky guess that turns out true is not knowing; neither is a true belief held for no reason. Epistemology asks what must be added to true belief to get knowledge. The kind in question is propositional knowledge: knowing that something is the case, as opposed to knowing how to do something or knowing a person.
The justified true belief analysis
The classical analysis, traceable to Plato's Theaetetus, holds that S knows that p if and only if three conditions are met:
- Truth: p is true (you cannot know a falsehood).
- Belief: S believes that p (you cannot know what you do not believe).
- Justification: S is justified in believing p (you have adequate reasons or evidence, not a lucky guess).
Each condition seems necessary, and together they were long thought sufficient. The justification condition is meant to rule out lucky guesses.
The Gettier problem
In a three-page paper in 1963, Edmund Gettier presented cases where all three JTB conditions are met yet we would not say the person knows, because the belief is true by luck. A standard example: Smith has strong evidence that Jones will get a job and that Jones has ten coins in his pocket, so Smith infers "the person who gets the job has ten coins." In fact Smith himself gets the job, and Smith happens to have ten coins. Smith's belief is true, believed and justified, yet it is true only by coincidence, so it is not knowledge. The justification did not connect to what made the belief true.
The lesson: JTB is not sufficient for knowledge. There is a gap between being justified and the belief's being non-accidentally true.
Proposed responses
- No false lemmas (Gilbert Harman and others): add that the justification must not rely on any false belief. In the Gettier case, Smith's reasoning passed through the false belief that Jones would get the job, so this rules it out. Objection: some Gettier cases involve no false premise (for example "fake barn" cases).
- Reliabilism (Alvin Goldman): replace or supplement justification with the requirement that the belief be produced by a reliable process. In Gettier cases the lucky route is not reliable. Objection: the fake-barn case shows a reliable-looking perception can still yield a lucky truth.
- Defeasibility theory: knowledge is justified true belief for which there is no defeater, no further truth that, if known, would undermine the justification. The unknown truth (Smith will get the job) is such a defeater.
- Causal / safety / sensitivity conditions: require the right causal or modal connection between the fact and the belief, so the belief could not easily have been false.
No single repair is universally accepted, and some epistemologists conclude that knowledge may be unanalysable into simpler conditions.
Test the belief in a Gettier-style case condition by condition.
Step 1: Describe the case
You look at a stopped clock that happens to read 3:00 at exactly 3:00, and you form the belief "it is 3:00". Check each JTB condition in turn.
Step 2: Verify truth, belief and justification
Truth: it really is 3:00, so the truth condition holds. Belief: you do believe it is 3:00. Justification: reading a clock is normally a good reason, so the belief is justified. All three JTB conditions are satisfied.
Step 3: Show why it is not knowledge
The clock is broken and stopped; it would read 3:00 whatever the actual time. Your justified true belief is true only by luck, because the justification (the reading) is disconnected from what makes it true. So this is a counterexample to JTB's sufficiency.
Step 4: Apply a candidate fourth condition
A safety condition (the belief could not easily have been false) explains the verdict: had you looked a minute earlier or later, the stopped clock would have made your belief false, so it is unsafe and not knowledge. This shows how anti-luck conditions are meant to repair JTB.
A belief can be true, believed and well justified yet fail to be knowledge because it is true only by luck, the justification being disconnected from what makes it true. Every proposed repair tries to add a condition that excludes this kind of epistemic luck, which is why the Gettier problem reshaped modern epistemology.
- Saying Gettier refutes the truth or belief conditions
- It targets sufficiency: the three conditions are met yet there is no knowledge.
- Treating JTB as obviously wrong from the start
- The conditions each seem necessary; Gettier's point is the surprising one that together they are not sufficient.
- Confusing reliabilism with the no-false-lemmas fix
- Reliabilism is about the process; no-false-lemmas is about the premises used in reasoning.
- Forgetting that the truth is lucky
- What disqualifies a Gettier belief as knowledge is that its truth is accidental relative to the justification.
Try this
Q1. State the three conditions of the justified true belief analysis. [3 marks]
- Cue. p is true; S believes p; S is justified in believing p.
Q2. Explain how a Gettier case shows JTB is not sufficient for knowledge. [4 marks]
- Cue. All three conditions are met, but the belief is true only by luck, so it is not knowledge.
Q3. Outline one proposed repair to the JTB analysis. [3 marks]
- Cue. For example reliabilism: the belief must be produced by a reliable process, excluding the lucky route.
Exam-style questions
Questions in the style of QCAA exam questions on this dot point, each with a worked answer. They are written by ExamExplained unless tagged "Past paper"; the year shows the paper a question is modelled on.
Practice7 marksExplain the justified true belief analysis of knowledge and evaluate it in the light of the Gettier problem.Show worked answer →
A 7 mark response sets out JTB, the Gettier challenge, and a verdict.
JTB. S knows that p if and only if: p is true (you cannot know a falsehood), S believes p (you cannot know what you do not believe), and S is justified in believing p (adequate reasons, not a lucky guess). Each condition seems necessary, and together they were thought sufficient.
Gettier. Gettier (1963) gives cases meeting all three conditions where there is no knowledge because the belief is true by luck. For example Smith justifiably infers "the person who gets the job has ten coins" from evidence about Jones, but Smith himself gets the job and happens to have ten coins: true, believed, justified, yet only accidentally true. So JTB is not sufficient.
Evaluation. The conditions remain plausibly necessary, but Gettier shows a gap between justification and non-accidental truth. The analysis needs a fourth condition (no false lemmas, reliability, no defeaters, or a safety/sensitivity link) to exclude epistemic luck.
Verdict. JTB is a strong first approximation but, as it stands, fails on sufficiency; the live question is which anti-luck condition repairs it.
Markers reward the three conditions, an accurate Gettier case, and the conclusion that JTB is necessary-looking but not sufficient.
Practice5 marksCompare the no-false-lemmas response and reliabilism as attempts to solve the Gettier problem, and assess each against the fake-barn case.Show worked answer →
A 5 mark response states both repairs and tests them on fake barns.
No false lemmas. Adds that the justification must not depend on any false belief. It handles the original Gettier case, where Smith reasoned through the false belief that Jones would get the job.
Reliabilism. Requires the belief to be produced by a reliable process rather than (or as well as) being justified. The lucky Gettier route is not reliable.
Fake-barn test. Henry sees a real barn in an area full of convincing fake barns and believes "that is a barn". His belief is true and his perception involves no false premise (defeating no-false-lemmas) and perception is generally reliable (straining reliabilism), yet intuitively he does not know, since he could so easily have looked at a fake. The case pressures both repairs and motivates safety or sensitivity conditions.
Markers reward accurate statements of both responses and the point that fake barns challenge each.