Lexical diffusion

Similar views were expressed by Romance dialectologists in the late 19th century but were reformulated and renamed by William Wang and coworkers studying varieties of Chinese in the 1960s and the 1970s.

The principle was summarized by the Neogrammarians in the late 19th century in the slogan "sound laws suffer no exceptions" and forms the basis of the comparative method of reconstruction and the tree model of linguistic evolution.

[3] Inspired by the Uniformitarian Principle of geology, Neogrammarians such as Hermann Paul described regularity as a consequence of the operation of sound change as an imperceptible articulatory drift conditioned by the phonetic environment.

[9] Uniform sound change was first challenged by Hugo Schuchardt, a dialectologist of Romance languages, who wrote in his criticism of the Neogrammarians:[10][11] Rarely-used words lag behind; very frequently used ones rush ahead.

[28] They present a revised model that distinguishes between the initial "actuation" of a sound change by language contact or internal factors, and its "implementation" by lexical diffusion.

Schematic diagram of a uniform sound change, a gradual change that applies equally to all words [ 2 ]
The vowel of the word sun in England
Schematic diagram of lexical diffusion, in which an abrupt change spreads through the lexicon [ 15 ]