linguistic drift

is the idea that language moves down-time in a current of its own making. Even if it were a self-contained unity it would drift, turning into a new language. Dialects combine the drift of language with the drift of people.

If individual variations 'on a flat' were the only kind of variability in language, I believe we should be at a loss to explain why and how dialects arise, why it is that a linguistic prototype gradually breaks up into a number of mutually unintelligible languages. But language is not merely something that is spread out in space, as it were a series of reflections in individual minds of one and the same timeless picture. Language moves down time in a current of its own making. It has a drift. If there were no breaking up of a language into dialects, if each language continued as a firm, self-contained unity, it would still be constantly moving away from any assignable norm, developing new features unceasingly and gradually transforming itself into a language so different from its starting point as to be in effect a new language. Now dialects arise not because of the mere fact of individual variation but because two or more groups of individuals have become sufficiently disconnected to drift apart, or independently, instead of together. So long as they keep strictly together, no amount of individual variation would lead to the formation of dialects. In practice, of course, no language can be spread over a vast territory or even over a considerable area without showing dialectic variations, for it is impossible to keep a large population from segregating itself into local groups, the language of each of which tends to drift independently. Under cultural conditions such as apparently prevail to-day, conditions that fight localism at every turn, the tendency to dialectic cleavage is being constantly counteracted and in part 'corrected' by the uniformizing factors already referred to. Yet even in so young a country as America the dialectic differences are not inconsiderable.(language 157-160)

linguistic drift, n.All

linguistic drift