I-mutation

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/ (a voiced palatal approximant, sometimes called yod, the sound of English in yes).