It may be said, therefore, that consanguinity is not always considered as the essence of kinship. If now we wish to determine what are the common features of the different ideas which in different societies define kinship, the only answer is that the said ideas affirm in one way or another a very close, intimate tie between offspring and parents. These ideas may refer kinship to physiological facts (consanguinity as found in the major part of human societies); or they may base kinship on the performance of a quite conventional ceremony (Todas, Banks Islanders); or they may affirm a very close tie between parent and child, on the base of some religious or magic belief (spiritual tie, transmission of soul: the Naudoweissies and some Australian tribes, as will be seen below). It is evident, therefore, that the general idea of kinship cannot be construed in terms of any of these special sets of ideas. The essential features that must be claimed for these ideas (_i. e._ those ranged in the class of kinship ideas) are: (1) that they must refer to the relation between child and father or mother;[533] and (2) that they must affirm an intimate bond of union of some kind between the parties involved. As may be easily conceived, it will be difficult in very low societies to get hold of these ideas, that is, to obtain the exact answer to the question, "What is kinship?" It is now impossible even to measure exactly the difficulty of getting a precise answer to this question, as ethnographers have never paid special attention to this point. Nevertheless, in Australia we shall be able to get at least some glimpses, which are of the highest theoretical interest. And even the negative result--that the idea of consanguinity must be considered wanting in the majority of Australian tribes--is of considerable theoretical value. [533] The terms _child_, _father_ and _mother_ being defined first broadly as explained above, pp. 172 _sqq._ Besides the general question, "What is considered as the source of parental (maternal and paternal) kinship?" we may ask questions about the various other ideas connected with kinship. Here come in the legal, moral, and customary ideas, by which society exercises its normative power in reference to the said relation. Some of these are expressed in different social functions.[534] Others may be reached by the study of beliefs, traditions, customs and other forms of folk-lore. The well-known customs of the _couvade_ are one of the typical functions of the father, in which there is an expression of a deep connection of a magical kind between the father and his offspring. Whatever explanation of these customs may be given,[535] it cannot be denied that they are based upon the idea of a very intimate tie between the two individuals involved, and that this tie is conceived as being of a mystical character.