Lexical diffusion
Evaluation
Evaluation
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Labov found evidence for both processes, but argued that they operate at different levels:
* Regular sound change occurs when the phonetic realization of a phoneme varies gradually and continuously. The process affects all words containing the phoneme uniformly. Examples include [vowel shifts](/wiki/Vowel_shift "Vowel shift") and [diphthongization](/wiki/Diphthongization "Diphthongization"), weakening of [glides](/wiki/Semivowel "Semivowel") and unstressed vowels, [vocalization of liquids](/wiki/L-vocalization "L-vocalization"), and changes in the [manner of articulation](/wiki/Manner_of_articulation "Manner of articulation") of consonants.
* Lexical diffusion represents a change in the phonemes in a word (substitution, [metathesis](/wiki/Metathesis_%28linguistics%29 "Metathesis (linguistics)"), [elision](/wiki/Elision "Elision"), [epenthesis](/wiki/Epenthesis "Epenthesis")). It is abrupt and applies to words selected by lexical, grammatical or social criteria.
[Paul Kiparsky](/wiki/Paul_Kiparsky "Paul Kiparsky") argues that under a proper definition of analogy as optimization, lexical diffusion is a non\-proportional type of analogy similar to [leveling](/wiki/Morphological_leveling "Morphological leveling"), rather than a type of sound change.


Can you give an example of a vowel shift?