Lesson · 4 min Steady
The Measure
In one line Protagoras made each person the measure of how things are to them. Ask where that holds and where it breaks.
The Sophists were paid teachers who came to Athens in the fifth century BCE to teach the skills of public life, above all speaking in assemblies and courts. The most famous, Protagoras of Abdera, opened a book by saying that a human being is the measure of all things, of what is and of what is not.
Plato read this as saying that whatever seems true to a person is true for that person. If the wind feels cold to me and warm to you, there is no further fact. Protagoras also said he could not know whether the gods exist, because the question is obscure and life is short.
Plato objected that if each belief is true for its holder, so is the belief that Protagoras is wrong. The habit worth keeping is to sort questions of how things seem from questions of how they are.
Go deeper
Scholars still disagree about what Protagoras meant. Some read the measure line as a claim about perception: the wind really is cold for the one who feels it cold. Others read it as a broader relativism about values and laws, which fits the Sophists’ interest in how customs differ from city to city. Plato’s Theaetetus is the main source, and it was written by a critic, so the real position may have been more careful than the one Socrates attacks.
Too hot, too cold
Two coworkers argue about the office. One says it is too hot, the other that it is too cold. For a while each tries to prove the other wrong.
Then they notice that both reports can be accurate, because each is about how the room feels to that person. The thermometer settles a different question, the temperature. Once the two questions are apart, they move one desk nearer the window.
Try this today In your next disagreement, ask whether it is about how something seems to each of you, or how it is.
Cite or share this lesson
A plain reference you can paste into notes or an essay:
Quest2Reason. “The Measure.” https://quest2reason.com/learn/lesson/the-measure. Accessed 13 November 2026.
Sources
- Stanford Encyclopedia of Philosophy, “Protagoras” — Covers the measure doctrine, his agnosticism and Plato’s objections in the Theaetetus.
- Internet Encyclopedia of Philosophy, “Sophists” — Overview of the Sophists as paid teachers and of how Plato and later historians judged them.