The question may be raised whether the single family should remain the primary social unit, or whether a group of families united in close coöperation would better fulfil the purposes for which the family exists. The privacy and separateness of each family would not need to be disturbed, coöperation might be limited to specific objects, such as simplifying the work of the household, providing kindergarten education for the young children, better play facilities, separate study rooms for adolescents, common entertainments for all, and a service of song at the beginning or close of the day. One obvious difficulty in constituting such a group would be: the diversities of tastes and opinions, particularly such as are not perceived at the outset, but emerge on nearer acquaintance, and as the younger members grow up and develop their idiosyncrasies. One great advantage, however, would result if care were taken to include in the group persons belonging to different vocations—scientist, scholar, architect, lawyer, artist. Young persons as they mature would then have the benefit of contact with those who are intimately familiar with different lines of vocational activity, and would be helped to know their own mind as to their future career better than they commonly do now. Personal contact with one who is engaged in a certain line of work is a far better instruction as to the nature of the work than reading about it or observation from a distance. The ethical theory of marriage has been developed in my published addresses.[73] But certain topics not there treated I would at least allude to here in passing, and among them the need of a more careful study of the causes that lead to infelicity in marriage. Kant mentions, as an instance of the discrepancy between the natural and the moral order, the fact that the sex passion is often at its height before the period when marriage may be wisely entered into. There are other seemingly radical incongruities, for instance, that between the face, the features of a person and his real character. The one may be borrowed so to speak from some ancestor, while the real nature is quite at variance with the impression created by the face, so that one who thinks he marries A really marries B. There are diversities also between partners in marriage that only show themselves in the latter part of life, when the outlines of character are apt to stand forth bare. Besides, there is assumed to be, by some modern writers, a certain fundamental sex antagonism.