Wave model
![Diagram based on the Wave model originally presented by Johannes Schmidt. In this Euler diagram, the circles are to be regarded as diachronic; that is, they increase in diameter over time, like the concentric waves on a water surface struck by a stone. The background represents a dialect continuum of no language boundaries. The circles are stable dialects, characters or bundles of characters that have been innovated and have become more stable over an originally small portion of the continuum for socio-political reasons. These circles spread from their small centers of maximum effectiveness like waves, becoming less effective and then dissipating at maximum time and distance from the center. Languages are to be regarded as impermanent sets of speech habits that result from and prevail in the intersections of the circles. The most conservative language is represented by the area not covered by the circles.](/Images/godic/202502/20/Wave_model_Schmidt.svg3638.png")
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 a central region of origin in continuously weakening concentric circles, similar to the waves created when a stone is thrown into a body of 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 characters, 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 has 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.