The Germanic umlaut (sometimes called i-umlaut or i-mutation) is a type of linguistic umlaut in which a back vowel changes to the associated front vowel (fronting) or a front vowel becomes closer to /i/ (raising) when the following syllable contains /i/, /iː/, or /j/. It took place separately in various Germanic languages starting around AD 450 or 500 and affected all of the early languages except Gothic. An example of the resulting vowel alternation is the English plural foot ~ feet (from Proto-Germanic *fōts, pl. *fōtiz). Germanic umlaut, as covered in this article, does not include other historical vowel phenomena that operated in the history of the Germanic languages such as Germanic a-mutation and the various language-specific processes of u-mutation, nor the earlier Indo-European ablaut (vowel gradation), which is observable in the conjugation of Germanic strong verbs such as sing/sang/sung. While Germanic umlaut has had important consequences for all modern Germanic languages, its effects are particularly apparent in German, because vowels resulting from umlaut are generally spelled with a specific set of letters: ä, ö, and ü, usually pronounced /ɛ/ (formerly /æ/), /ø/, and /y/.