Protagoras
Sophist · Europe · 490 to 420 BCE
Travelling teacher of the Sophists who is remembered for saying that a person is the measure of all things.
What it is
Protagoras was a Greek thinker of the fifth century BCE, born in Abdera, and one of the most important of the sophists, teachers who earned a living by training people in argument and public speaking. He is best known for the saying that man is the measure of all things.
That saying has been read as the first clear statement of relativism, the view that what is true or right depends on the person judging. He also wrote about the gods, saying that he could not tell whether they exist, and he is a leading character in two of Plato's dialogues.
The main ideas
- Man is the measure. He held that of all things the measure is man, of what is that it is and of what is not that it is not. It is usually read to mean that things are for each person as they appear to that person.
- Teaching argument. He taught for pay, and his teaching was centred on skill in argument and speech, including making a case on both sides of a question.
- Doubt about the gods. In a work on the gods he said he could not tell whether they exist or not, which is why he is called an early agnostic.
- Law and justice as human agreement. His view of justice and law was conventionalist, resting on what people agree, not on what the gods command.
What it looks like in practice
Picture two neighbours who disagree about whether a room is too warm, one in a coat and one in shirtsleeves. For Protagoras, each is right about how it is for them, and the real work is to persuade each other which way of living with the temperature is better. This is an illustration of the idea, not a saying of Protagoras.
Books and moments
- Truth and On the Gods are the two books named for him, and only fragments survive.
- Plato's Protagoras and Theaetetus are the two dialogues in which he appears or is discussed at length.
- The impiety story. Several ancient writers say he was tried for impiety and his books burned, but this may be a later legend.
Questions and criticism
- Is every view as true as any other? The saying is often read as relativism, but some scholars caution that the label may not fit him exactly.
- Is relativism good for democracy? Some readers think his view fits democracy, since laws can be changed by debate, while others doubt that he meant it that way.
- Is teaching argument for pay a good thing? Plato and Socrates criticised the sophists for this, and the question of whether skill in argument serves truth or only winning is still asked.
Close neighbours
Socrates and Plato argued against him. The page on Plato sets out the reply, and the page on Socrates shows the opposite approach to questions.
Written by epchē in our own words, and checked against independent sources on 9 October 2026. The sources are listed below.
Who they connect to
Reacted against by
- Plato · Plato argued against the claim that a person is the measure of all things.
- Socrates · Plato's Protagoras shows Socrates disputing the Sophist's claim to teach virtue. (scholars disagree about this link)
Other Sophist thinkers
- Gorgias · 483 to 375 BCE
Sources we used
- Protagoras · Stanford Encyclopedia of Philosophy, read on 9 October 2026
- Protagoras · Internet Encyclopedia of Philosophy, read on 9 October 2026
- Protagoras · New World Encyclopedia, read on 9 October 2026
- Protagoras · Wikipedia, read on 9 October 2026