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The question then arises, who is to fix the rate? the man who

first gives, or the man who first takes? because, prima facie,

the man who first gives seems to leave the rate to be fixed by

the other party. This, they say, was in fact the practice of

Protagoras: when he taught a man anything he would bid the

learner estimate the worth of the knowledge gained by his own

private opinion; and then he used to take so much from him. In

such cases some people adopt the rule,

"With specified reward a friend should be content."

They are certainly fairly found fault with who take the money in

advance and then do nothing of what they said they would do,

their promises having been so far beyond their ability; for such

men do not perform what they agreed, The Sophists, however, are

perhaps obliged to take this course, because no one would give a

sixpence for their knowledge. These then, I say, are fairly found

fault with, because they do not what they have already taken

money for doing.