Old High German , which does not, both from Proto-Germanic . That may mean that there was dialectal variation in the timing and spread of the two changes, with final loss happening before umlaut in the south but after it in the north. On the other hand, umlaut may have still been partly allophonic, and the loss of the conditioning sound may have triggered an "un-umlauting" of the preceding vowel. Nevertheless, medial consistently triggers umlaut although its subsequent loss is universal in West Germanic except for Old Saxon and early Old High German. I-mutation in Old English I-mutation generally affected Old English vowels as follows in each of the main dialects. It led to the introduction into Old English of the new sounds , (which, in most varieties, soon turned into ), and a sound written in Early West Saxon manuscripts as but whose phonetic value is debated. I-mutation is particularly visible in the inflectional and derivational morphology of Old English since it affected so many of the Old English vowels. Of 16 basic vowels and diphthongs in Old English, only the four vowels were unaffected by i-mutation. Although i-mutation was originally triggered by an or in the syllable following the affected vowel, by the time of the surviving Old English texts, the or had generally changed (usually to ) or been lost entirely, with the result that i-mutation generally appears as a morphological process that affects a certain (seemingly arbitrary) set of forms. These are most common forms affected: The plural, and genitive/dative singular, forms of consonant-declension nouns (Proto-Germanic (PGmc) ), as compared to the nominative/accusative singular – e.g., "foot", "feet"; "mouse", "mice". Many more words were affected by this change in Old English vs. modern English – e.g., "book", "books"; "friend", "friends". The second and third person present singular indicative of strong verbs (Pre-Old-English (Pre-OE) , ), as compared to the infinitive and other present-tense forms – e.g. "to help", "(I) help", "(you sg.) help", "(he/she) helps", "(we/you pl./they) help". The comparative form of some adjectives (Pre-OE < PGmc , Pre-OE < PGmc ), as compared to the base form – e.g. "old", "older", "oldest" (cf. "elder, eldest"). Throughout the first class of weak verbs (original suffix ), as compared to the forms from which the verbs were derived – e.g. "food", "to feed" < Pre-OE ; "lore", "to teach"; "to fall", "to fell". In the abstract nouns