In a recent article, Westphal has drawn attention to two important points which are in danger of being forgotten in attempts at linguistic classification:
1. Phonetic and phonological, lexical, morphological, and other relationships may differ as between the languages being compared. ‘Thus if we say two languages are related, we usually mean something more specific, e.g. they are phonologically related, they are morphologically related, they are lexically related, etc.’
2. In attempting to determine ‘genetic’ relationship, we should be careful not to speak about any language as if there were always only one ‘parent’. Not only may there be more than one ‘ancient language’ involved, but these may have come into the ‘family tree’ at different historical periods, so that one language or group of languages may have evolved from the impingement of one or more other language types upon a substratum. Languages that are of mixed origin in this sense are probably more common than has been suspected, and it would be possible to classify any such language (or group) in a number of different ways according to the different criteria mentioned under (1) above. Even on the plane of lexical relationships, the recent discussions on the position of the ‘Nilo-Hamitic’ languages show that reasonable claims for the ‘Niloticism’ or ‘Hamiticism’ of these languages can be made, the point at issue resolving itself into a statistical one of percentages of words related to one or other of the two Larger Units, Nilotic and Hamitic.