Amongst the heterogeneous factors which together make up parental kinship, the physiological facts appear to be the most constant, for the natural process of procreation is in all human societies the same. But the social consequences of this process vary very widely according to other variable elements, as will appear clearly below in our discussion of consanguinity. Part of them only, together with some social elements, may be taken as the uniform, constant basis of kinship, such as must serve for the first point of departure in an attempt to discuss more in detail the kinship in any society. It appears probable that this basis is given by the existence of a group formed by a woman, her husband, and the children whom she has borne, suckled and reared. The existence of such a group will be considered as the necessary and sufficient condition for _individual parental kinship_. Where such a group exists we are justified in affirming that individual parental kinship exists, although it is not yet completely defined thereby; further facts must be adduced in order to complete the definition. Those further facts are precisely the variable terms in the general formula of kinship; it remains still to indicate their general character. But a few words must be first said about the constant factors of kinship just mentioned. They consist in the existence of the individual family group as determined by individual marriage and by individual motherhood. Individual motherhood means that the same woman who gave birth to a child stands to it in a special close relation in its later life also: she suckles it and rears it, and she is bound to him or her by the manifold ties resulting from the community of life and community of interests. This woman is bound on the other hand to a man by individual marriage; and thereby her children are bound to him also; and the mother, her husband, and her children form the social unit called the individual family. The existence of such a unit is to be established by showing its different social functions, and the different ways in which its solidarity and individuality are marked in a given society. It is clear that the position of the father is in this way first established socially only, as the husband of the children's mother. Nevertheless it must be borne in mind that thus his relation to the children is clearly marked; and that this is only a preliminary, so to say formal, determination of fatherhood, which in all societies appears to be much more materially defined by other factors, discussed hereafter.