A general outline of the foundations for a theory of language change. The first section is devoted to a critical review of the relevant literature (primarily the theory of H.Paul, and its heritage in Saussure, Bloomfieldianism, and generative grammar); the second section considers problems of change on the basis of various relevant theoretical concepts; the third section, finally, proposes a model of language as a differentiated system, showing how language functions as the structure changes, and thus avoiding the paradoxes of earlier theories.