These also are different from one another; for that of parent for child is not the same as that of ruler for subject, nor even that of father for son the same as that of son for father, nor that of man for woman the same as that of woman for man. For each of these classes has a different excellence and a different function, and the grounds of their affection are different; therefore their love and their friendship also are different. What each does for the other, then, is not the same, nor should they expect it to be the same; but when children give to their parents what they owe to those who begat them, and parents on their part give what they owe to their children, then each friendship will be lasting, and what it ought to be. But in all friendships based on inequality, the love on either side should be proportional⁠—I mean that the better of the two (and the more useful, and so on in each case) should receive more love than he gives; for when love is proportioned to desert, then there is established a sort of equality, which seems to be a necessary condition of friendship.