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 (raising) when the following syllable contains , , or . 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 , pl. ). 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: , , and , usually pronounced /ɛ/ (formerly /æ/), /ø/, and /y/. Umlaut is a form of assimilation or vowel harmony, the process by which one speech sound is altered to make it more like another adjacent sound. If a word has two vowels with one far back in the mouth and the other far forward, more effort is required to pronounce the word than if the vowels were closer together; therefore, one possible linguistic development is for these two vowels to be drawn closer together. Description Germanic umlaut is a specific historical example of this process that took place in the unattested earliest stages of Old English and Old Norse and apparently later in Old High German, and some other old Germanic languages. The precise developments varied from one language to another, but the general trend was this: Whenever a back vowel (, or , whether long or short) occurred in a syllable and the front vowel or the front glide occurred in the next, the vowel in the first syllable was fronted (usually to , , and respectively). Thus, for example, West Germanic "mice" shifted to proto-Old English , which eventually developed to modern mice, while the singular form lacked a following and was unaffected, eventually becoming modern mouse. When a low or mid-front vowel occurred in a syllable and the front vowel or the front