Theaetetus (171)

SOC. And what of Protagoras himself? If neither he himself thought, nor people in general think, as indeed they do not, that man is the measure of all things, is it not inevitable that the truth which he wrote is true to no one? But if he himself thought it was true, and people in general do not agree with him, in the first place you know that it is just so much more false than true as the number of those who do not believe it is greater than the number of those who do.

THEO. Necessarily, if it is to be true or false according to each individual opinion.

SOC. Secondly, it involves this, which is a very pretty result; he concedes about his own opinion the truth of the opinion of those who disagree with him and think that his opinion is false, since he grants that the opinions of all men are true.

THEO. Certainly.

SOC. Then would he not be conceding that his own opinion is false, if he grants that the opinion of those who think he is in error is true?

THEO. Necessarily.

SOC. But the others do not concede that they are in error, do they?

THEO. No, they do not.

SOC. And he, in turn, according to his writings, grants that this opinion also is true.

THEO. Evidently.

SOC. Then all men, beginning with Protagoras, will dispute—or rather, he will grant, after he once concedes that the opinion of the man who holds the opposite view is true—even Protagoras himself, I say, will concede that neither a dog nor any casual man is a measure of anything whatsoever that he has not learned. Is not that the case?

THEO. Yes.

SOC. Then since the truth of Protagoras is disputed by all, it would be true to nobody, neither to anyone else nor to him.

THEO. I think, Socrates, we are running my friend too hard.

SOC. But, my dear man, I do not see that we are running beyond what is right. Most likely, though, he, being older, is wiser than we, and if, for example, he should emerge from the ground, here at our feet, if only as far as the neck, he would prove abundantly that I was making a fool of myself by my talk, in all probability, and you by agreeing with me; then he would sink down and be off at a run. But we, I suppose, must depend on ourselves, such as we are, and must say just what we think. And so now must we not say that everybody would agree that some men are wiser and some more ignorant than others?

THEO. Yes, I think at least we must.

SOC. And do you think his doctrine might stand most firmly in the form in which we sketched it when defending Protagoras, that most things—hot, dry, sweet, and everything of that sort—are to each person as they appear to him, and if Protagoras is to concede that there are cases in which one person excels another, he might be willing to say that in matters of health and disease not every woman or child—or beast, for that matter—knows what is wholesome for it and is able to cure itself, but in this point, if in any, one person excels another?

THEO. Yes, I think that is correct.