Plato, Protagoras, and Predictions

Plato's Theaetetus discusses and ultimately rejects Protagoras's famous claim that "man is the measure of all things." The most famous of Plato's arguments is the Self-Refutation Argument. But he offers a number of other arguments as well, including one that I call the 'Future Argument.' This argument, which appears at Theaetetus 178a−179b, is quite different from the earlier Self-Refutation Argument. I argue that it is directed mainly at a part of the Protagorean view not addressed before, namely, that all beliefs concerning one's own future sensible qualities are true. This part of the view is found to be inconsistent with Protagoras's own conception of wisdom as expertise and with his own pretenses at expertise in teaching.