Aristotle, Nicomachean Ethics
H. Rackham, Ed.

The friendship between husband and wife appears to be a natural instinct; since man is by nature a pairing creature even more than he is a political creature,² inasmuch as the family is an earlier and more fundamental institution than the State, and the procreation of offspring a more general³ characteristic of the animal creation. So whereas with the other animals the association of the sexes aims only at continuing the species, human beings cohabit not only for the sake of begetting children but also to provide the needs of life; for with the human race division of labor begins at the outset, and man and woman have different functions; thus they supply each other's wants, putting their special capacities into the common stock. Hence the friendship of man and wife seems to be one of utility and pleasure combined. But it may also be based on virtue, if the partners be of high moral character; for either sex has its special virtue, and this may be the ground of attraction. Children, too, seem to be a bond of union, and therefore childless marriages are more easily dissolved; for children are a good possessed by both parents in common, and common property holds people together.