The Greek philosopher Protagoras (ca. 484-ca. 414 B.C.) was one of the best-known and most successful teachers of the Sophistic movement of the 5th century B.C.
Protagoras was born in Abdera, the native city of Democritus, and spent much of his life as an itinerant Sophist, traveling throughout the Greek world. He was a frequent visitor to Athens, being a friend of Pericles, and was said to have aided in framing the constitution for the colony of Thurii, which the Athenians established in southern Italy in 444/443 B.C. Plato said that Protagoras spent 40 years teaching and that he died at the age of 70. Stories about an indictment against Protagoras by the Athenians, the burning of his books, and his death at sea are probably fictitious.
Protagoras earned his livelihood giving lectures and instruction to individuals and groups. The system he taught had little to do with philosophy or the pursuit of an absolute truth; instead it imparted to its adherents the necessary skills and knowledge for success in life, especially in politics. These skills consisted mainly of rhetoric and dialectic and could be used for whatever ends a person desired. It was for this reason, for teaching people "to make the weaker cause the stronger, " that Protagoras came under attack, indirectly by Aristophanes in The Clouds and directly by Plato in several of his dialogues.
Protagoras wrote on a wide variety of subjects. Fragments of some of his works survive, and the titles of others are known through later comments on them. His famous dictum "man is the measure of all things" is the opening sentence of a work variously called Truth or Refutatory Arguments. He also wrote On the Gods, a fragment of which survives. In it he says that the obscurity of the subject and the shortness of human life prevent any definite conclusions. Other works include The Great Argument, Contradictory Arguments, On Mathematics, and The Art of Eristics. The list of titles preserved in the works of the Greek biographer Diogenes Laertius may represent sections of larger works, whereas such titles as On Ambition, On Virtues, On Human Errors, and Trial Concerning a Fee almost certainly represent discussions of the common themes of Sophistic speeches. The chronology of these works is unknown.
Protagoras was a perfect example of the 5th-century Sophist. Careful thinkers could, of course, easily undermine the basis of his relative theory of knowledge; but the attractiveness of his theory and the pervasive influence of his teachings were so great that no less an opponent than Plato went to great lengths to expose the fallacies and potential evil of what he represented.
The surviving fragments of Protagoras's works are collected in H. Diels and W. Kranz, Die Fragmente der Vorsokratiker, translated in Kathleen Freeman, Ancilla to the Pre-Socratic Philosophers (1948), and discussed in her The Pre-Socratic Philosophers (1946; 3d ed. 1953). An excellent discussion of the Sophists and their contributions to Greek culture is in Werner Jaeger, Paideia: The Ideals of Greek Culture, translated by Gilbert Highet, vol. 1 (1939; 2d ed. 1945). A brief but useful account of Protagoras's importance can be found in Albin Lesky, A History of Greek Literature (1966).