Protagoras (c. 481-411 B.C.), a Greek philosopher, was born at Abdera. In the dialogue with the same name, Plato calls him the first of the Sophists, because Protagoras accepted payment for his teachings. He also acted as a teacher in Athens and was banished from the city for impiety. His most famous saying is his homo mensura-statement "Man is the measure of all things."
He learned philosophy in the Ionian school, and was perhaps a pupil of Democritus, though this is doubtful on chronological grounds. He was an older contemporary of Socrates. He was so highly esteemed by Pericles that he was entrusted with the task of framing laws for the new colony of Thurii (Plut. Pericles, 36). At the age of seventy, having been accused by Pythodorus, and convicted of atheism, Protagoras fled from Athens, and on his way to Sicily was lost at sea. According to Plato (Prot., 318 E), he endeavoured to communicate "prudence" (6130vXia) to his pupils, "which should fit them to manage their households, and to take part by word and deed in civic affairs." The education which he provided consisted of rhetoric, grammar, style and the interpretation of the poets. His formal lectures were supplemented by discussions amongst his pupils. He left behind him several treatises, of which only a few fragments have survived. In Truth, by way of justifying his rejection of philosophy or science, he maintained that "man is the measure of all things - of what is, that it is, and of what is not, that it is not." Besides Truth, and the book Of the Gods which caused his condemnation at Athens, Diogenes Laertius attributes to him treatises on political, ethical, educational and rhetorical subjects. Protagoras was the first to systematize grammar, distinguishing the parts of speech, the tenses and the moods. Besides Truth, and the book Of the Gods which caused his condemnation at Athens, Diogenes Laertius attributes to him treatises on political, ethical, educational and rhetorical subjects. Protagoras was the first to systematize grammar, distinguishing the parts of speech, the tenses and the moods.
According to Plato, the meaning of "Man is the measure of all things" is that all things appear to each person the way they seem to be at that moment. Protagoras seems to have held a skeptic and relative view on knowledge, with no place for absolute, universal statements. As for the gods, Protagoras held an agnostic view. He said that he did not know if they existed or not. The span of life was too short for a human being to answer this difficult question.
Sources and references
Encyclopaedia Britannica 11th edition, public domain