ABSTRACT
Surely, I said, knowledge is the food of the soul; and we must take care, my friend, that the Sophist does not deceive us when he praises what he sells, like the dealers wholesale or retail who sell the food of the body; for they praise indiscriminately all their goods, without knowing what are really beneficial or hurtful: neither do their customers know, with the exception of any trainer or physician who may happen to buy of them. In like manner those who carry about the wares of knowledge, and make the round of the cities, and sell or retail them to any customer who is in want of them, praise them all alike; though I should not wonder, O my friend, if many of them were really ignorant of their effect upon the soul; and their customers equally ignorant, unless he who buys of them happens to be a physician of the soul. If, therefore, you have understanding of what is good and evil you may safely buy knowledge of Protagoras or any one; but if not, then, O my friend, pause, and do not hazard your dearest interests at a game of chance. For there is far greater peril in buying knowledge than in buying meat and drink. . . .
