Protagoras of Abdera in Thrace (c. 490–420 B.C.E.) was the most acclaimed of all the Sophists. Plato wrote that he was the first Sophist to call himself a Sophist. He trained young men for politics and was friends with the statesman Pericles (c. 495–429 B.C.E.), who asked him to write a constitution for the new colony of Thuri. He was a productive writer, and his works included “On Truth,” “On the Gods,” and “Antilogic,” none of which have survived to this day. Protagoras was the author of the humanistic credo “Man is the measure of all things, of all things that are, that they are and of things that are not that they are not.”

Protagoras held that the soul is nothing above or beyond a person’s perceptions. His relativism was based on the different perceptual experiences of different individuals; for instance, what is cold to one person may seem warm to another. And he extended the relativism of individual experience to large groups in claiming that “whatever is just to a city is just for that city so long as it seems so.”

However, although all perceptions and ideas of justice are true, according to Protagoras, he thought that some were better than others. He felt that it was the job of the Sophist to change people’s minds so that they had better ideas about what was just and beautiful. The better perceptions and ideas were those that had better consequences. In other words, the Sophists taught their “clients” how to succeed.