1. No one would choose to live without friends if he had all other goods.
2. When people are friends, they have no need of justice, but when they are just, they need friendship in addition.
3. We conclude, therefore, that to be friends, men must have good will for one another, must each wish for the good of the other on the basis of one of three motives(the good, the pleasant, and the useful), and must each be aware of one another’s good will.
4. The three motives differ from one another in kind, and so do the corresponding types of affection and friendship.
5. Now, when the motive of the affection is usefulness, the partners do not feel affection for one another as such, but in terms of the good accruing to each from the other. The same is also true of those whose friendship is based on pleasure; we love witty people not for what they are, but for the pleasure they give us… Accordingly, with the disappearance of the motive for being friends, the friendship, too, is dissolved, since the friendship owed its existence to these motives.
6. The perfect form of friendship is that between good people who are alike in excellence or virtue. For these friends wish alike for one another’s good because they are good people, and they are good as such… Hence, their friendship lasts as long as they are good, and that means it will last a long time, since goodness or virtue is a thing that lasts.

— From Book 8 of the Nicomachean Ethics by Aristotle