Mr. Thomas, at the end of a passage in which he discusses the relation between the concepts of kinship and consanguinity says that in Australia "some relation will almost certainly be found to exist between the father and child; but it by no means follows that it arises from any idea of consanguinity." So far we perfectly agree with the reasoning of the author. But when Mr. Thomas adds, "In other communities _potestas_[541] and not _consanguinity_[541] is held to determine the relations of the husband of a woman to her offspring; and it is a matter for careful inquiry how far the same holds good in Australia, when the fact of fatherhood is in some cases asserted to be unrecognized by the natives,"[542] we see that he falls into the error of acknowledging only two possibilities: potestas or consanguinity. It is true that he speaks of consanguinity as being modified by native ideas, and that thus a social element is introduced into the physiological concept of consanguinity. But we are still left to guess how this social element is to be understood. And as pointed out above, the relation between father and child in the tribes in question cannot be considered as based upon consanguinity or community of blood, whatever meaning we give to these words. Erroneous in any case is the opposition of kinship and potestas, as if these two concepts were of the same order, and could be considered as two equivalent categories excluding each other. Whereas, as we saw, these two concepts are of quite different order and cannot be treated as excluding or replacing each other. Kinship is a very complicated social fact, very complex in its sociological and psychological aspects. _Potestas_ is a legal category, expressing a set of attributes and rights of the father over his children. Potestas (or any analogous legal factor) may be a constituent element of kinship in certain societies. It cannot possibly replace kinship entirely. [541] The italics are mine. [542] _Loc. cit._, p. 5.