It is evident why mothers love their children more than fathers. The procreation of children is the universal function of animals. In the case of other animals, this is the limit of their association; but men and women unite not only for the procreation of children but for the purposes of life. As soon as they unite, a distribution of functions takes place. Some are proper to the husband and others to the wife; hence they supply one another’s needs, each contributing to the common stock. Utility and pleasure seem alike to be found in the marriage relationship, but its basis will be virtue, too. Children are a bond of union, and such marriages as are childless are dissolved with comparatively little difficulty.[8] The _Politics_ begin with a discussion of slavery, and, by an association of ideas natural in Greek society, for Aristotle never attempts to rise above the conditions of life about him, slaves and women are treated together: He who can foresee with his mind is by nature intended to be lord and master; and he who can work with his body is a subject, and by nature a slave: hence, master and slave have the same interest. Nature, however, has distinguished between the female and the slave. For she is not niggardly; she makes each thing for a single use, and every instrument is best made when intended for one and not for many uses. But among barbarians no distinction is made between women and slaves. It should be noticed here that the essential quality of the master is not physical strength, but mental capacity; it is the mind and not the body that makes the ‘natural’ slave, the ‘live tool,’ as Aristotle defines him. Man and woman, master and slave, these are the foundations of the family. As Hesiod says: ‘First a house, then a woman, and then an ox for the plough’; and Aristotle has no difficulty in finding the arrangement right. He puts the question: Is there any one intended by nature to be a slave, so that for him the condition of slavery is expedient and right; or, rather, is not all slavery a violation of nature? And gives the immediate reply: There is no difficulty in answering this question on grounds both of reason and of fact. For that some should rule and others be ruled is a thing not only necessary but expedient; from the hour of their birth some are marked out for subjection, others for rule. The law, he thinks, holds through all nature: Tame animals have a better nature than wild, and all tame animals are better off when they are ruled by men, for then they are preserved. The male is by nature superior, and the female inferior; and the one rules and the other is ruled; this principle of necessity extends to all mankind. Nature would like to distinguish between the bodies of freemen and slaves; but this does not hold universally.