Fragments

Protagoras of Abdera, the most famous of the Older Sophists and a paid teacher of rhetoric and civic virtue across the Greek world, is known chiefly through his declaration, quoted by Plato and later writers, that 'man is the measure of all things,' a claim usually read as asserting that truth, or at least perceptual truth, is relative to each individual rather than objective and universal. His treatise On Truth survives only in this fragment and later paraphrase; a companion work, On the Gods, opened by declaring that he could not know whether the gods exist, a statement of agnosticism that reportedly led to his prosecution and exile from Athens. Plato's dialogue named for him presents Protagoras defending the teachability of civic virtue against Socrates's skepticism.