Aristotle, Nicomachean Ethics
H. Rackham, Ed.

[2] Now in these unequal friendships the benefits that one party receives and is entitled to claim from the other are not the same on either side; but the friendship between parents and children will be enduring and equitable, when the children render to the parents the services due to the authors of one's being, and the parents to the children those due to one's offspring. The affection rendered in these various unequal friendships should also be proportionate¹: the better of the two parties, for instance, or the more useful or otherwise superior as the case may be, should receive more affection than he bestows; since when the affection rendered is proportionate to desert, this produces equality in a sense between the parties, and equality is felt to be an essential element of friendship. [3]

Equality in friendship, however, does not seem to be like equality in matters of justice. In the sphere of justice, ‘equal’ （fair） means primarily proportionate to desert, and ‘equal in quantity’ is only a secondary sense; whereas in friendship ‘equal in quantity’ is the primary meaning, and ‘proportionate to desert’ only secondary. [4] This is clearly seen when a wide disparity arises between two friends in point of virtue or vice, or of wealth, or anything else; they no longer remain nor indeed expect to remain friends. This is most manifest in the case of the gods, whose superiority in every good attribute is pre-eminent;