Germanic a-mutation

A-mutation is a metaphonic process supposed to have taken place in late Proto-Germanic (c. 200).

In a-mutation, a short high vowel (*/u/ or */i/) was lowered when the following syllable contained a non-high vowel (*/a/, /o:/ or /æ:/). Thus, since the change was produced by other vowels besides */a/, the term a-mutation is something of a misnomer. It has also been called "a-umlaut", "a/o-umlaut", "velar umlaut" and, formerly, "Brechung". (This last was Grimm's term, but nowadays German Brechung, and its English equivalents breaking and fracture, are generally restricted in use to other unrelated sound-changes which later affected individual Germanic languages)

The high vowel was not lowered, however, if */j/ intervened between it and the following non-high vowel. An intervening nasal consonant followed by a consonant of any kind also blocked the process (and raised original */e/ to */i/).

a-mutation seems to have preceded the raising of unstressed final */o:/ to */u:/ in the dialects ancestral to Old English and Old Norse, hence in Old English the phenomenon is subject to many exceptions and apparent inconsistencies which are usually attributed to a mixture of paradigmatic levelling and phonetic context.

a-mutation is more evident in some Germanic languages than others. It is widely found in Old High German, less so in other West Germanic languages and Old Norse.a-mutation is less extensive in Old East Norse (the precursor of Danish and Swedish) than Old West Norse (spoken in Norway and its colonies). There is no trace of it at all in Gothic, where the distinction between the short high and mid vowels had become allophonic (Proto-Germanic /e/ and /i/ merged).Old Gutnish, at the eastern end of the territory where Old Norse evolved, resembles Gothic in this respect. But there is some suggestion that a-mutation may have been preserved in Crimean Gothic.

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