The Gettier Problem

In brief

Edmund Gettier (1927 to 2021) published a paper of barely three pages in the journal Analysis in 1963, titled "Is Justified True Belief Knowledge?" His answer was no. For most of the history of philosophy, knowledge had been understood as justified true belief: to know that something is the case, you must believe it, it must be true, and you must have adequate justification for believing it. Gettier described short scenarios in which a person satisfies all three conditions and yet, by common consent, does not know. The belief is true, but true by accident, its justification pointing at the truth only through a piece of luck. The paper detonated a definition that had gone essentially unchallenged since Plato, and it launched a research program, still unfinished, into what knowledge actually is.

The full treatment

The definition it breaks

The target is the classical, or tripartite, analysis of knowledge, usually abbreviated JTB. A subject S knows that a proposition P is true if and only if three conditions all hold: P is true, S believes that P, and S is justified in believing that P. Each condition earns its place. Truth is required because you cannot know a falsehood. Belief is required because you cannot know something you do not even accept. Justification is required to rule out lucky guesses: a person who believes the correct lottery number on a hunch, and happens to be right, does not thereby know it. The three conditions are meant to be jointly sufficient, so that anything meeting all three counts as knowledge. Gettier's achievement was to show they are not.

Gettier's construction

Gettier's method is a recipe. Take a belief that is well justified but false. Deduce from it a further belief that happens, by luck, to be true. The second belief inherits the justification of the first (valid deduction transmits justification), so it is justified. It is true. It is believed. Yet the person does not know it, because the justification runs through a falsehood and the belief lands on the truth only by accident.

His first case: Smith and Jones have applied for a job. Smith has strong evidence for the proposition "Jones will get the job, and Jones has ten coins in his pocket," having been told by the company president and having just counted Jones's coins. From this he infers "the man who will get the job has ten coins in his pocket." But it is Smith, not Jones, who gets the job, and Smith, as it happens, also has ten coins in his pocket, a fact he had not checked. Smith's belief that the man who will get the job has ten coins is true, and justified, and believed. We deny that he knows it. His evidence was about Jones; the truth is about himself; the match is a coincidence.

His second case sharpens the point with pure logic. Smith is justified in believing "Jones owns a Ford," on strong evidence. From this he constructs the disjunction "Either Jones owns a Ford, or Brown is in Barcelona," where Brown is an acquaintance whose whereabouts Smith knows nothing about. A true disjunction needs only one true disjunct. As it turns out, Jones does not own a Ford, but Brown, by sheer chance, is in Barcelona. The disjunction is true, Smith believes it, and it is validly deduced from justified premises, so it is justified. Again, no knowledge.

Why the cases bite

What both cases isolate is a form of luck. The Athenian philosophers had a word for the aim of inquiry, but the modern diagnosis is crisp: in a Gettier case the connection between the justification and the truth is severed and then reconnected by accident. Good reasoning is supposed to be truth-conducive because it tracks the facts. In Gettier's scenarios the reasoning is impeccable and the conclusion true, yet the reasoning tracks the wrong facts, and the belief is rescued by a coincidence the reasoner did nothing to earn. Knowledge, the intuition says, cannot be that lucky. The problem is that JTB contains nothing to exclude luck of this kind.

The repairs

Three families of response dominate. The first, and most obvious, is to add a fourth condition. Michael Clark proposed in 1963 that a knower's belief must be "fully grounded," containing no false premises, the so-called no-false-lemma or no-false-grounds requirement. This handles Gettier's own cases neatly, since both run through a falsehood. But Alvin Goldman and others soon produced Gettier-style cases with no false lemma at all, the most famous being the "barn facade" case (a driver truly and justifiedly believes she sees a barn, in a district full of convincing fake barns, and happens to be looking at the one real one). No falsehood is involved; luck alone defeats knowledge.

The second family abandons justification as the third condition and looks instead at the causal or nomic relation between fact and belief. Alvin Goldman, in "A Causal Theory of Knowing" (1967), argued that S knows P only if the fact that P is causally connected in the right way to S's believing it. In Gettier's cases the truth does not cause the belief, so no knowledge. Goldman himself later replaced this with reliabilism: a belief counts as knowledge when it is produced by a reliable process, one that generally yields truths. Robert Nozick, in Philosophical Explanations (1981), offered a related "tracking" account built on counterfactuals: you know P only if, were P false, you would not believe it (sensitivity), and were P true in slightly different circumstances, you still would (adherence). Fred Dretske and others developed similar externalist theories, which locate knowledge in the relation between mind and world rather than in reasons the knower can cite.

The third response, more radical, is to stop trying to define knowledge in independent parts at all. That is where the deepest critics have gone.

Lineage

The definition Gettier attacked traces to Plato (c. 428 to c. 348 BCE). In the Theaetetus (c. 369 BCE), Socrates and the young mathematician Theaetetus test the proposal that knowledge is true belief accompanied by an account, a logos, and the dialogue famously ends in failure, unable to pin the account down. The tripartite formula that later philosophers extracted from it became the received view, largely unexamined, through the modern period. Both the rationalist project of Rene Descartes (1596 to 1650), seeking beliefs secured against doubt, and the empiricist scrutiny of David Hume (1711 to 1776), asking what our beliefs about the world are really grounded in, assume that knowledge is justified true belief and dispute only what the justification can be. Gettier's paper is short partly because it needed no history: it simply took the definition everyone shared and broke it in three pages. The result was one of the most cited short works in twentieth-century philosophy.

The strongest case for it

The Gettier problem is not a thesis one argues for; it is a discovery, and its force is that almost no one who understands the cases can bring themselves to call the beliefs knowledge. That near-universal reaction is the data. It shows that our concept of knowledge contains more than truth, belief, and justification: it contains a demand that the truth of the belief not be accidental relative to its grounds, an anti-luck condition that the classical analysis silently omitted. The value of Gettier's move is that it converted a vague sense that "something more is needed" into a precise, reproducible test. Any proposed analysis of knowledge can now be checked by attempting to Gettierize it, and the fact that this test keeps succeeding against new analyses is itself a substantive finding about how the concept is built.

The strongest case against it

The sharpest resistance does not deny the cases but questions the program they launched. Linda Zagzebski, in "The Inescapability of Gettier Problems" (1994), argued that the whole enterprise of adding a fourth condition is doomed in principle. Her argument: so long as justification (or any third component) is independent of truth, meaning a belief can be justified yet false, you can always construct a case where the belief is false for reasons the justification does not touch, then twist the scenario so the belief comes out true by luck. Gettier cases are therefore not a bug to be patched but a structural feature of any analysis that treats knowledge as truth plus independent components. If she is right, the fifty-year hunt for the missing condition was chasing a mirage.

Timothy Williamson pressed the more drastic conclusion. In Knowledge and Its Limits (2000) he inverted the traditional order: knowledge is not to be analyzed into belief, truth, and justification at all. Knowing is a basic mental state, prime and unanalyzable, and belief and justification should be understood partly in terms of it, not the reverse. On this "knowledge-first" view the Gettier problem is real but the reaction to it was wrong: the failure to define knowledge in more basic terms is not a puzzle to be solved but a sign that the definitional project was misconceived from Plato onward. A separate strand, the epistemic-luck literature developed by Duncan Pritchard and others, accepts that knowledge excludes luck but argues that no simple condition captures the right kind of luck, since knowledge tolerates some forms of luck (you can luckily be in a position to see something) while excluding others. Pinning down exactly which luck is fatal has proved as hard as the original problem.

Where it stands now

There is no agreed solution, and the consensus among epistemologists is that the classical analysis, as stated, is false. Beyond that the field divides. Some still pursue a corrected analysis, typically an anti-luck or "safety" condition (roughly: your belief could not easily have been false). Reliabilists and other externalists claim the problem is dissolved once justification is dropped for a truth-tracking relation, though internalists reply that this abandons the very idea that a knower has reasons. Williamson's knowledge-first program has a large following that regards the search for a definition as closed. What is not disputed is Gettier's impact. A three-page paper with no jargon and two toy stories reset a two-thousand-year-old question and made "epistemology after Gettier" a distinct era. Few philosophers have overturned so much with so little.

Test yourself

Recall the coins case: Smith rightly believes "the man who will get the job has ten coins," but only because he unknowingly matches a description he formed about someone else. Now try to state, in one sentence, the extra condition that his belief lacks and real knowledge has. If your sentence uses the words "luck" or "accident," you have found the gap; the harder task, and the one still unsolved, is saying precisely which accidents knowledge forbids and which it can survive.