Protagoras Quotes

“Socrates : 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?
Theodorus : Necessarily.
Socrates : But the others do not concede that they are in error, do they?
Theodorus : No, they do not.
Socrates : And he, in turn, according to his writings, grants that this opinion also is true.
Theodorus : Evidently.
Socrates : 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?
Theodorus : Yes.
Socrates : Then since the “truth” of Protagoras is disputed by all, it would be true to nobody, neither to anyone else nor to him.
[171b-c]”
― Plato, Theaetetus