True belief and epistemic luck › What the proposed analysis promises

Imagine checking a meeting time on a normally dependable office display. It says 10:30, so you believe it is 10:30. Unknown to you, the display froze yesterday. By coincidence, you happen to look at it at exactly 10:30 today. Your belief is true, and consulting the display seemed reasonable. Whether you knew the time is a further question.

This invented version of a familiar epistemological puzzle introduces the distinction Edmund Gettier examines in "Is Justified True Belief Knowledge?" A person can have good grounds, reach a true conclusion, and still arrive at that truth through an accidental match. Gettier's two examples put pressure on an analysis that identifies knowledge with justified true belief. Their conclusion does not imply that evidence is pointless or that knowledge is impossible.

The analysis concerns propositional knowledge: knowing that something is the case. It does not directly analyze knowing a person or knowing how to ride a bicycle. Let P stand for a proposition and S for a person. The proposal says that S knows P if and only if P is true, S believes P, and S is justified in believing P.

The phrase "if and only if" makes a demanding claim. Each condition is presented as necessary: knowledge requires it. The three conditions together are presented as sufficient: satisfying them guarantees knowledge. A counterexample to sufficiency needs a case in which all three conditions hold and knowledge is absent. Showing that somebody has a justified false belief would not accomplish that, because the truth condition would already fail.

Belief and truth do different work. Someone can believe a meeting begins at 10:30 when it begins at eleven. Equally, the meeting's actual start time does not ensure that someone who has never heard of it believes anything about it. Justification introduces a third question: what standing does the person's belief have, given the evidence or reasons available?

The initials JTB abbreviate justified true belief. The brevity of the formula can conceal how much turns on its last component. What counts as justification is itself a philosophical dispute. The JTB formula alone leaves justification undefined; Gettier supplies two preliminary points about it. The formula does not by itself settle whether justification depends entirely on what the believer can reflectively access.

Gettier's paper appeared in Analysis 23, issue 6, in June 1963, on pages 121–123. It begins with recent attempts to state conditions for knowledge and discusses formulations by Roderick Chisholm and A. J. Ayer alongside the familiar three-part proposal. That is a more accurate account of its immediate target than a story in which one uncontested definition ruled philosophy unchanged for two thousand years. Gettier, p.121.