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I-mutation (also known as umlaut, front mutation, i-umlaut, i/j-mutation or i/j-umlaut) is an important type of sound change, more precisely a category of regressive metaphony, in which a back vowel is fronted, and/or a front vowel is raised, if the following syllable contains /i/, /ī/ or /j/ (voiced palatal approximant the sound of English <y> in ‘yes’).

I-mutation has occurred in many languages (for example, it explains the alternations between Portuguese fiz < */fetsi/ "I did" vs. fez < */fetse/ "he did") and nowadays it is still productive in some Romance languages (for instance Central Venetian where final -i is still visible te parchigi < */parchégi/ "you park your car" vs. parchégio "I park"). However, the term is usually taken (especially when referred to using the name "i-umlaut") to processes in the early Germanic languages. I-mutation in the Romance languages is more commonly called "metaphony" (from Ancient Greek, meaning "process of changing sounds"); Umlaut is its rendering in German.

I-mutation is usually used to refer to a particular set of changes in the old Germanic languages. I-mutation is particularly important because it was productive in the prehistory of the Germanic languages and led to many alternations that are visible in the morphology of these languages, due to the prevalence of inflectional suffixes containing an /i/ or /j/.

This process took place separately in the various Germanic languages starting around 450 or 500 AD in the North Sea area, and affected all of the early languages^[1] except for Gothic.^[2] It seems to have taken effect earliest, and was most complete in its implementation, in Old English and Old Norse. It took place later in Old High German, and by 900 AD its effects were visible only on /a/. (However, there are occasional spellings with y, ui, iu and oi, suggesting that /o/ and /u/ were already affected allophonically.)

For more information on the process in the Germanic languages, see Germanic umlaut.

Notes[link]

1. ^ See Fausto Cercignani, Early "Umlaut" Phenomena in the Germanic Languages, in «Language», 56/1, 1980, pp. 126-136.
2. ^ See Fausto Cercignani, Alleged Gothic Umlauts, in «Indogermanische Forschungen», 85, 1980, pp. 207-213.

See also[link]

• Affection - i-mutation in the Celtic languages
• Germanic umlaut
• Old English phonology