Irish initial mutations

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Irish, like all modern Celtic languages, is characterized by its initial consonant mutations.^[1] These mutations affect the initial consonant of a word under specific morphological and syntactic conditions. The mutations are an important tool in understanding the relationship between two words and can differentiate various meanings.

Irish, like Scottish Gaelic and Manx, features two initial consonant mutations: lenition (Irish: séimhiú [ˈʃeːvʲuː]) and eclipsis (urú [ˈʊɾˠuː]) (the alternative names, aspiration for lenition and nasalisation for eclipsis, are also used, but those terms are misleading).

Originally these mutations were phonologically governed external sandhi effects: lenition was caused by a consonant being between two vowels, and eclipsis when a nasal preceded an obstruent, including at the beginning of a word.

Irish also features t-prothesis and h-prothesis, related phenomena which affect vowel-initial words.

See Irish phonology for a discussion of the symbols used on this page.