The family in the narrower sense includes merely those persons who are naturally and most directly united through marriage and immediate descent, that is to say, spouses and children. In the larger sense, however, one includes in it the totality of those descended from a common ancestor, and this probably includes also those linked to it by marriage; indeed, domestics are also included in the concept of the family, because they, too, are partners in the communal life of the family, which is one of the chief characteristics of the family in the narrower sense. Three (or four) different kinds of relationships, fundamentally different one from the other, thus exist united in the family, and just as many principles are accordingly relevant for its reasoned legal order. A reasonable family law can be derived not from the general law of society, but only from the special legal nature of these three or four relationships: to wit, that between the spouses; that between parents and children (the relationship between the children is of little concern); and, finally, that between masters and servants. We shall take a brief look at these three (or four) relationships.
Marriage is the first foundation of the family. What is marriage from the perspective of the law of reason? In agreement with common sense, it would be difficult to define it as anything other than a union between man and woman, entered into for the purpose of the enjoyment of sexual love in accordance with the law of morality and with the nobler nature of man. For it is only this definition that satisfies the idea of the dignity, indeed the sacredness, of marriage that exists among all the civilized peoples, and even among those who still live in natural simplicity,
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What constitutes the moral foundation of marital law, then, is that the purpose of marriage cannot be the satisfaction of the sexual impulse as such (for otherwise man would be equal to the animals), but only a refined satisfaction, that is, one in accord with the higher human dignity and man’s nature as a creature of reason. The refinement of this impulse, however, is achieved through love, which directs all its strength at a single person, and desires sexual pleasure as nothing other than the expression of this love, as the most intimate union with the beloved. Furthermore, the natural consequence of sexual union points to the natural purpose of the sexual urge – the propagation of the species, and thus the obligation to satisfy this impulse only in accordance with this purpose. The requisite refinement of the sexual urge lies in the sincere cultivation of that emotion and in the honest, active recognition of that duty, and reasonable marital law arises from the establishment of this refinement as the character and purpose of marriage.