Gettier Case: Epistemology Glossary

Gettier case (noun): a counterexample to the classical definition of knowledge as justified true belief, in which a subject’s justified conviction happens to be true, but only through accidental coincidence, so that it cannot count as knowledge.

The term derives from American philosopher Edmund Gettier, who in 1963 published a short, epoch-making paper titled "Is Justified True Belief Knowledge?" In four pages, he presented two scenarios designed to show that the three traditional conditions for knowledge — belief, truth, and justification — are jointly insufficient.

If you found this valuable, consider supporting our work.

Anatomy of a Gettier Case

Every Gettier case shares a common structure:

• The subject holds a belief that is true.
• The belief is justified — meaning the subject has evidence or reasons that, from their perspective, make the belief reasonable.
• The justification is defective in a subtle way, because it connects to the truth only via an accidental factor.
• The subject therefore lacks knowledge, even though all three JTB conditions are satisfied.

The most famous examples are Gettier's own. In the first, Smith has strong evidence that Jones will get the job and also knows Jones has ten coins in his pocket. Smith infers that the person who gets the job will have ten coins in his pocket. Unbeknownst to Smith, he himself gets the job, and he also has ten coins. His belief is true and justified, but its truth has nothing to do with the evidence he actually used. In the second case, Smith believes "Jones owns a Ford or Brown is in Barcelona" because he has strong evidence that Jones owns a Ford. The disjunction turns out true because Brown is in Barcelona, not because of Jones's car. Again, justified and true — but not knowledge.

"Borrowing a term from contemporary analytic philosophy, we can say that a Gettier case is any scenario in which a justified true belief is nevertheless an instance of thin epistemic luck."

Philosophers often distinguish between intervening luck (where the world messes with your evidence to make the belief true) and environmental luck (where your evidence is fine, but the surrounding world is deceptive). Gettier cases typically involve a combination of both. The belief is true, but the truth "happens to" land on the belief without the belief system reliably tracking the world.

The legacy of the Gettier case is enormous: it triggered multiple sub-fields, including epistemic luck, virtue epistemology, reliabilism, and contextualism. No matter which theory of knowledge you encounter, it is almost certain to be framed as a response to Gettier. The term remains essential for any serious student of philosophy.

Related terms: justified true belief, epistemic luck, reliabilism, virtue epistemology, no false lemma, safety condition, sensitivity condition, Edmund Gettier.