Compensatory lengthening

Compensatory lengthening in phonology and historical linguistics is the lengthening of a vowel sound that happens upon the loss of a following consonant, usually in the syllable coda, or of a vowel in an adjacent syllable. Lengthening triggered by consonant loss may be considered an extreme form of fusion (Crowley 1997:46). Both types may arise from speakers' attempts to preserve a word's moraic count.

An example from the history of English is the lengthening of vowels that happened when the voiceless velar fricative /x/ and its palatal allophone [ç] were lost from the language. For example, in the Middle English of Chaucer's time the word night was phonemically /nixt/; later the /x/ was lost, but the /i/ was lengthened to /iː/ to compensate, causing the word to be pronounced /niːt/ ("neet"). (Later the /iː/ became /aɪ/ by the Great Vowel Shift.)

Both the Germanic spirant law and the Ingvaeonic nasal spirant law show vowel lengthening compensating for the loss of a nasal.

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