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Wellsprings
epistemology

The Criterion of Truth

κριτήριον

The ultimate yardstick a philosophy uses to sort the true from the false — its answer to the question of what we should finally trust.

The criterion of truth is the standard or faculty by which we judge whether something is true or false. Different philosophical schools disagreed sharply about what this standard should be. Some held that man himself, or human perception, served as the criterion; others argued it was the senses, reason, or what the Stoics called the apprehensive presentation—a clear and vivid impression that compels assent. This problem was central to ancient epistemology, the study of knowledge itself.

The disagreement over criteria had practical consequences. Skeptics weaponized this very problem: if we cannot agree on how to recognize truth in the first place, they argued, we cannot prove anything is true at all. This circular problem—needing a criterion to judge the criterion itself—became a powerful tool in skeptical reasoning and forced philosophers like the Stoics to defend why their chosen standard deserved trust above all others.

Where this idea shows up

56 Greek sources

Where to read it