Protagoras (d. 420 BCE) was a pre-Socratic Greek philosopher born in Abdera, northeast Greece who traveled and lectured widely.

Protagoras became the advisor to Athenian democrat Pericles, the ruler of the city-state of Athens, who instructed him to write the constitution for the colony of Thurii in 444 BCE. Although traveling widely, Protagoras spent most of his time in Athens. As a teacher, he earned a living from lecturing in oratory, public speaking, grammar, and poetry, and was known for the high fees. Ancient legends that accumulated around Protagoras and that are likely unhistorical tell of stories of his studying with the atomist philosopher Democritus, being jailed for his views, having his works and intellectual material burned, and him fleeing from Athens.

Much of what historians know about Protagoras comes from Plato’s (d. 348 BCE) writings. Plato referred to Protagoras as a sophist. Historically, these men were traveling intellectuals and experts in rhetoric who taught others how to speak in assemblies and law courts. Such skills were both necessary and highly valued within Athenian society. The sophists were often private tutors to the youth of the upper classes.

Perhaps the major theme to come out of Protagoras’ thought is his subjectivist philosophy. He argued that interpretations of reality are relative to individuals as expressed in his statement that “Man is the measure of all things: of the things that are, that they are, of the things that are not, that they are not.” Protagoras also claimed to be able to make the worse (or weaker) argument seem better or stronger. Theologically, he claimed that humans are unable to tell whether or not the gods existed.  Protagoras was agnostic, possibly even atheistic, concerning the Greek pantheon of gods. This, some historians have suggested, could have been behind the burning of his books by the Athenians.

Protagoras’ subjectivist philosophy likely did not mean that he did not believe truth to exist; rather, he likely meant that one’s understanding and apprehension of truth is relative to individual perception. What a person holds to be true will be true to that individual despite any evidence to the contrary. Within this lies arguably his greatest contribution to Western thought which is that one person might perceive something in the world radically different from what his neighbour sees. According to legend, Protagoras was charged with the significant offense of impiety. Evidently while fleeing the colony of Sicily he drowned in the sea.