Protagoras

Protagoras was born in Abdera in Thrace, probably in the 490s BCE, and travelled the Greek world as a paid teacher, becoming famous and rich; Plato credits him with being the first to adopt the title of sophist openly. He stayed in Athens at least twice and knew Pericles, who in 444 entrusted him with writing laws for the new colony of Thurii in southern Italy. Later stories say that he was tried for impiety, that his books were burned and that he drowned fleeing Athens, but these are doubtful: Plato writes as if he died old and respected, at about seventy.

Fewer than ten genuine fragments survive, so his thought is known mostly through Plato, who gave him a dialogue of his own, the Protagoras, and examined his “measure” doctrine at length in the Theaetetus, and through Aristotle and Sextus Empiricus. Democritus, a younger man from the same city, argued that the doctrine undermines itself, and Plato and Aristotle developed the objection. His separation of justice from the will of the gods, and his confidence that ordinary citizens can judge political questions, have been read as a theoretical basis for Athenian democracy.