Defining knowledge: Plato's justified true belief and the Gettier counterexamples

What this dot point is asking

This dot point belongs to Unit 1 of the TASC Philosophy course, which introduces epistemology as the branch of philosophy concerned with the nature and sources of knowledge. You are asked to state the standard definition of knowledge, explain why it is attractive, and then evaluate it against the most famous objection in modern epistemology.

The tripartite analysis

The classical definition traces back to Plato's dialogue the Theaetetus, where Socrates explores the idea that knowledge is true belief with an account or logos. Later philosophers crystallised this into three individually necessary and jointly sufficient conditions. A subject S knows that a proposition P is true if and only if P is true, S believes that P, and S is justified in believing that P. Each condition does work. Truth rules out knowing falsehoods. Belief rules out knowing what you do not even accept. Justification rules out lucky guesses, since a correct guess is true belief without good reason.

Why the account is attractive

The JTB account captures a strong intuition: knowledge is more than getting lucky. If you flip a coin to decide whether it will rain and happen to be right, we would not say you knew it would rain, because your belief, though true, was not grounded. Justification is the ingredient that seems to convert mere true belief into knowledge. For more than two thousand years this looked like the right shape for a theory of knowledge.

Gettier's counterexamples

In a three-page paper, Edmund Gettier constructed cases where all three conditions hold yet we hesitate to grant knowledge. In one famous version, Smith has strong evidence that Jones will get a job and that Jones has ten coins in his pocket, so Smith infers that the person who will get the job has ten coins in their pocket. Unknown to Smith, Smith himself will get the job, and Smith happens also to have ten coins in his pocket. Smith's belief is true, he believes it, and it is justified by his evidence, yet it is true only by coincidence. Intuitively Smith does not know.

Responses to Gettier

Philosophers have tried several repairs. The no false lemmas response adds a condition that the belief must not be inferred from any false premise, since Smith reasoned through the false belief that Jones would get the job. Causal theories, defended by Alvin Goldman, require that the fact known cause the belief in the right way. Reliabilism, also associated with Goldman, replaces justification with the requirement that the belief be produced by a reliable process. Robert Nozick proposed a tracking or sensitivity condition: you know P only if, were P false, you would not believe it. Each proposal handles some cases but faces new counterexamples, and many epistemologists now doubt that any short list of conditions will work, a worry Linda Zagzebski generalised by showing how to construct Gettier cases for almost any added condition.

Evaluating the debate

A strong answer recognises what Gettier did and did not show. He did not prove that knowledge is impossible, only that the three conditions are not jointly sufficient. The lasting lesson is that knowledge seems to require a non-accidental link between a belief and the truth, and capturing that link precisely has proven remarkably hard. You can argue that the failure of repairs supports a different approach, such as treating knowledge as a basic state that cannot be analysed into simpler parts, a view defended by Timothy Williamson. For the exam, show that you can state JTB, deploy a Gettier case accurately, and weigh at least one repair.