The friendship of man and wife seems to be natural; for human beings are by nature more apt to join together in couples than to form civil societies, inasmuch as the family is prior in time to the state and more indispensable, and the propagation of the species is a more fundamental characteristic of animal existence. The other animals associate for this purpose alone, but man and wife live together not merely for the begetting of children, but also to satisfy the needs of their life: for the functions of the man and the woman are clearly divided and distinct the one from the other; they supply each other’s wants, therefore, both contributing to the common stock. And so this sort of friendship is thought to bring with it both pleasure and profit. But it will be based on virtue, too, if they be good; for each sex has its own virtue, and both will rejoice in that which is of like nature.

Children also seem to be a bond that knits man and wife together (which is a reason why childless unions are more quickly dissolved); for children are a good which both have in common, but that which people have in common holds them together.