SOCIAL ORGANISATION 63
if not conclusively, that the common nomenclature I am now considering has arisen out of the social \ need for emphasising the impropriety of relations which were once habitual among the people.
The second feature of Melanesian terminology which I have mentioned helps us to understand how the common nomenclature has come about. In most of the Melanesian cases in which a wife's sister is denoted by a term otherwise used for a sister, or a husband's brother by a term otherwise used for a brother, the term employed is one which is normally used between those of the same sex. Thus, a man does not apply to his wife's sister the term which he himself uses for his sister, but one which would be used by a woman of her sister. In other words, a man uses for his wife's sister the term which is used for this relative by his wife. This shows us how the common nomen- clature may have come into use. It suggests that as sexual relations with the wife's sister became no longer orthodox, a man came to apply to this woman the word with which he was already familiar as a term for this relative from the mouth of his wife. The special feature of Melanesian nomenclature according to which terms of relation- ship vary with the sex of the speaker here helps us to understand how the common nomenclature arose. The process is one in which psychological factors evidently play an important part, but these psychological factors are themselves the outcome of a social process, viz., the change from a con-