Quarrels arise also when the parties realise different results and not those which they desire; for the not attaining one’s special object is all one, in this case, with getting nothing at all: as in the well-known case where a man made promises to a musician, rising in proportion to the excellence of his music; but when, the next morning, the musician claimed the performance of his promises, he said that he had given him pleasure for pleasure: of course, if each party had intended this, it would have been all right: but if the one desires amusement and the other gain, and the one gets his object but the other not, the dealing cannot be fair: because a man fixes his mind upon what he happens to want, and will give so and so for that specific thing. The question then arises, who is to fix the rate? the man who first gives, or the man who first takes? because, _primâ 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. In cases where no stipulation as to the respective services is made they who disinterestedly do the first service will not raise the question (as we have said before), because it is the nature of Friendship, based on mutual goodness to be reference to the intention of the other, the intention being characteristic of the true friend and of goodness. And it would seem the same rule should be laid down for those who are connected with one another as teachers and learners of philosophy; for here the value of the commodity cannot be measured by money, and, in fact, an exactly equivalent price cannot be set upon it, but perhaps it is sufficient to do what one can, as in the case of the gods or one’s parents.