This great anthropological rift, however, is not due merely to the perversity and pugnacity of specialists, nor to any inherent vice of method or insufficiency of material. It often happens in science that the seemingly simplest and most fundamental prob lems are really the most difficult and remain longest debated and unsettled. As the physicists cannot make up their minds on matter, force or energy, as the chemists change their views on the atom and the elements, as the mathematicians are least certain about space, time and numbers, so the social anthropologists may be forgiven if they still debate, at times hotly, kinship—that con ception in which centre all their other problems and ideas.
This legal system is called mother-right (see MATRIARCHY), or more correctly matriliny; and the relation between a man and his sister's son, avunculate (q.v.). The circumstance that kin ship can be traced through both father and mother has been termed (by Lowie) "the bilateral principle of counting descent"; while the almost universal fact that in any given culture empha sis is laid upon one side only has been defined as the unilateral mode of regarding kinship. The bilateral aspect of kinship is never completely obliterated and unilateral counting only means a more or less limited emphasis on one side and never a complete elimination of the other.
Perhaps the most baffling and disquieting symptom of these col lective aspects of kinship is the queer linguistic usage known as the "classificatory" system of kinship nomenclature. In most savage tongues a man applies such terms as father, mother, brother, sister and so on, not only to the members of his family but, according to rules which vary with the social organization, to classes of people who stand in a definite relation to his parents. In some communities, indeed, for example in Australia, kinship terms go as far as actual social relations and even beyond—that is, even distant strangers never met or seen are regarded as poten tially belonging to one class of kindred or another.
Thus language and linguistic usage seem apparently to break the bonds of family, to obliterate parenthood by substituting a "group of fathers" for the individual one, a "group of mothers" for the real mother, and so on. Nor is this usage a mere rule of politeness : the "classificatory" terms are applied according to strict rules, to a number of people, whose relationship is traceable by pedigree or by membership in a clan or class. Behind the linguistic usage there is always a set of mutual obligations between an individual and all those whom he calls "fathers," "mothers," "brothers," etc. The "fathers" or "brothers" act as a group on certain occasions and they are therefore a well-defined social class and not merely a name.