Wave model

In historical linguistics, the wave model, or wave theory (German: Wellentheorie), is a model of language change in which a new language feature (innovation) or a new combination of language features spreads from its region of origin, being adopted by a gradually expanding cluster of dialects. Each innovation starts at a certain place, and spreads from speaker to speaker, from dialect to dialect, in the same fashion as waves on the water.

The theory was intended as a substitute for the tree model, which did not seem to be able to explain the existence of some features, especially in the Germanic languages, by descent from a proto-language. At its most ambitious, it is a wholesale replacement for the tree model of languages. During the 20th century, the wave model had little acceptance as a model for language change overall, except for certain cases, such as the study of dialect continua and areal phenomena; it has recently gained more popularity among historical linguists, due to the shortcomings of the tree model.