Protagoras

Protagoras worked in Greece around 490–420 BC, before Socrates walked Athens. Plato later grouped him with the sophists and credited him with inventing the professional version of that role. The trouble started with a book called Truth, where Protagoras wrote that each person's history and experience determine their judgments — what's true or good or beautiful shifts with the observer. Plato read it as pure relativism and attacked it; popular opinion recoiled. But Protagoras insisted the discomfort was the point: a working democracy requires you to respect others' perspectives even when they c…