- Lived:
- c. 490–420 BCE · born in Abdera, Thrace; famous in Athens
- Tradition:
- The first and greatest of the Greek Sophists — professional teachers of rhetoric and civic skill
- The Big Idea:
- Truth is not handed down from the cosmos or the gods; it is measured against human experience — so persuasion, law, and politics are where the real philosophical action is.
- In their words:
- "Man is the measure of all things: of things that are, that they are; of things that are not, that they are not."
- If you remember one thing:
- Twenty-five centuries before anyone said "post-truth," Protagoras asked the question we still can't put down: if every side of an argument feels true to somebody, what is truth?