Aristotle, Nicomachean Ethics
H. Rackham, Ed.

1. [2] In these business relationships then a common measure has been devised, namely money, and this is a standard to which all things are referred and by which they are measured. But in sentimental friendships, the lover sometimes complains that his warmest affection meets with no affection in return, it may be because there is nothing in him to arouse affection; while the person loved frequently complains that the lover who formerly promised everything now fulfils none of his promises. 1. [3] Such disputes occur when pleasure is the motive of the friendship on the lover's side and profit on the side of the beloved, and when they no longer each possess the desired attribute. For in a friendship based on these motives, a rupture occurs as soon as the parties cease to obtain the things for the sake of which they were friends; seeing that neither loved the other in himself, but some attribute he possessed that was not permanent; so that these friendships are not permanent either. But friendship based on character is disinterested, and therefore lasting, as has been said.¹ 1. [4]

Differences arise when the friends do not obtain what they desire, but something else; for not to get what you want is almost the same as not to get anything at all. For instance, there is the story of the man who hired a harper, and promised that the better he played the more he would pay him; but next morning, when the harper asked him to fulfil his promise, he said that he had already paid for the pleasure he had received by the pleasure he had given.² This would have been all right if both had wanted pleasure; but when one wants amusement and the other gain, and one gets what he wants and the other does not, it would not be a fair bargain; for it is the thing that a man happens to need that he sets his heart on, and only to get that is he ready to give what he does. 1. [5]

Which party's business is it to decide the amount of the return due? Should it be assessed by the one who proffers the initial service? Or rather by the one who receives³ it, since the other by proffering it seems to leave the matter to him? This we are told was the practice of Protagoras⁴; when he gave lessons in any subject, he used to tell his pupil to estimate the value he set upon his knowledge, and accepted a fee of that amount. 1. [6] In such matters however some people prefer the principle of ‘the wage stated.’⁵ But people who take the money in advance, and then, having made extravagant professions, fail to perform what they undertook, naturally meet with complaints because they have not fulfilled their bargain. 1. [7] Perhaps however the sophists are bound to demand their fees in advance, since nobody would pay money for the knowledge which they possess.⁶ Persons paid in advance then naturally meet with complaints if they do not perform the service for which they have taken the pay.

But in cases where no agreement is come to as to the value of the service, if it is proffered for the recipient's own sake, as has been said above,⁷ no complaint arises, for a friendship based on virtue does not give rise to quarrels;