Consonant mutation

Consonant mutation is change in a consonant in a word according to its morphological or syntactic environment.

Mutation phenomena occur in languages around the world. A prototypical example of consonant mutation is the initial consonant mutation of all modern Celtic languages. Initial consonant mutation is also found in Indonesian or Malay, in Southern Paiute and in several West African languages such as Fula. The Nilotic language Dholuo, spoken in Kenya, shows mutation of stem-final consonants, as does English to a small extent. Mutation of initial, medial, and final consonants is found in Modern Hebrew. Japanese exhibits word medial consonant mutation involving voicing, rendaku, in many compounds.

Initial consonant mutation must not be confused with sandhi, which can refer to word-initial alternations triggered by their phonological environment, unlike mutations, which are triggered by their morphosyntactic environment. Some examples of word-initial sandhi are listed below.

Sandhi effects like these (or other phonological processes) are usually the historical origin of morphosyntactically triggered mutation. For example, the English fricative mutation described above originates in an allophonic alternation of Old English, where a voiced fricative occurred between vowels (or other voiced consonants), and a voiceless one occurred initially or finally, and also when adjacent to voiceless consonants. Old English infinitives ended in -(i)an and plural nouns (of one very common declension class) ended in -as. Thus, hūs 'a house' had [s], while hūsas 'houses' and hūsian 'to house' had [z]. After most endings were lost in English, and the contrast between voiced and voiceless fricatives phonemicized (largely due to the influx of French loanwords), the alternation was morphologized.

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