The Measure of All Things

Two People, One Room

Two people sit in the same room. One reaches for a sweater and says it is cold. The other, who has just come in from a run, says it is warm. Neither is lying, and neither is confused. So which of them is right about the room?

You might say the thermometer settles it. But the thermometer reports a number, and the question was whether the room is cold. That depends on who is in it. A number of degrees that feels cold to one person feels pleasant to another. If you press the point, you may find yourself saying that the room is cold for her and warm for him, and that there is nothing further to be right about.

That small shrug opens a large question. If some things are true only for the person who experiences them, how far does that go? Does it stop at temperature and taste, or does it reach further, into what is just, what is healthy, what is real? A Greek teacher who lived about 2,400 years ago asked this question and gave an answer that people still argue about.

Who Protagoras Was

Protagoras was born in Abdera, in northern Greece, probably around 490 BCE, and he died around 420 BCE. These dates are approximate, as most dates for figures of this period are. He spent much of his working life in Athens and in other Greek cities, and he became the best known of a group called the sophists.

The sophists were traveling teachers who charged fees to instruct young men in argument and public speaking. In a democracy like Athens, where citizens argued their own cases in court and spoke in the assembly, these were valuable skills. The word ‘sophist’ comes from the Greek for ‘wise’, and at first it carried no insult. Plato, writing a generation later, distrusted the sophists because he thought they taught people to win arguments whether or not they were right, and took money for doing it.

This creates a problem for us. Almost none of Protagoras’s own writing survives. His most famous sentence comes down to us mainly through Plato, a hostile witness, and through later writers such as Sextus Empiricus and Diogenes Laertius. When we read Protagoras, we are usually reading someone else’s report of him.

The Claim Itself

In Plato’s dialogue Theaetetus, Socrates quotes the opening of a book by Protagoras. In Benjamin Jowett’s translation, the sentence reads: “Man is the measure of all things, of the existence of things that are, and of the non-existence of things that are not” (Plato, Theaetetus 152a, trans. Jowett, 1871). The Greek word translated ‘man’ is anthrōpos, which means a human being, not a male.

A measure is a standard we use to judge something, the way a ruler is the standard for length. Protagoras seems to be saying that human beings are the standard for judging what is and what is not. Socrates then offers his own reading: things are for each of us as they appear to each of us. He illustrates it with an example close to the one I opened with. The same wind blows on two people, and one feels cold while the other does not.

Read this way, the claim is a form of relativism, the view that truth depends on the person or group doing the judging. Plato’s Socrates goes on to argue that this view defeats itself. If every belief is true for the one who holds it, then the belief that Protagoras is wrong is true for those who hold it, and Protagoras must grant them that.

That objection is strong against the crudest version of the idea. In short, the crude version says: whatever you believe is true, because you believe it. It is not clear that Protagoras held that version. Scholars disagree about whether ‘man’ in his sentence means each individual person or human beings in general, and about how fairly Plato represents him. I do not think the surviving evidence settles either question.

Made and Tested by People

There is a more interesting reading, and Plato himself supplies material for it. Later in the Theaetetus, Socrates imagines Protagoras replying to his critics. In this imagined defense, Protagoras grants that one belief can be better than another. A sick person finds food bitter, and a healthy person finds it sweet. Neither is simply wrong about the taste, but the doctor who restores the sick person to health has changed things for the better. The wise person, on this account, is someone who can move people from worse appearances to better ones.

This is Plato’s reconstruction, so we should hold it loosely. But it points toward a reading of the famous sentence that has little to do with anything goes. On this reading, beliefs do not arrive from outside human life, stamped with a guarantee. People form them, people use them, and people find out whether they serve. The standard is human because there is no other place from which judging can be done.

Consider a more everyday case. A family has always believed that a certain route to the coast is the fastest. Nobody checked; it was simply what everyone knew. One summer the eldest daughter tries a different road and arrives twenty minutes earlier. The old belief did not become false the moment she tried the new road. It had been a human judgment all along, made from limited trips and old habits, and it was tested the same way it was made, by someone driving. The measure in this story is a person. That does not make the result arbitrary. It makes the result revisable.

This reading raises its own questions, and I want to be plain about them. If beliefs are better or worse depending on how they serve, we still need to say what ‘better’ means and who decides. Protagoras, as far as we can tell, did not give a full answer. What he left us is a sentence that puts human beings at the center of the question of truth and invites us to ask what follows.

Tomorrow we move forward more than two thousand years, to a group of American thinkers who took up that invitation. One of them described his view as a new name for some old ways of thinking (James, Pragmatism, 1907), and Protagoras is one of the old ways he had in mind.