Editing Germanic umlaut (section)

===North Germanic languages===
{{Main|Old Norse#Umlaut|l1=Old Norse umlaut}}
{{See also|Old Norse morphology}}Umlaut is a feature of Icelandic, in which both i-umlaut and a-umlaut exist.{{sfnp |Hansson |Wiese |2024 |pp=864–871 }} The situation in Old Norse is complicated as there are two forms of i-mutation. Of these two, only one is phonologized.{{Clarify|reason=Phonemic/etic? (In)effective?|date=August 2010}} I-mutation in Old Norse is phonological:
* In [[Proto-Norse]], if the syllable was [[syllable weight|heavy]] and followed by vocalic {{lang|mis|i}} ({{lang|mis|*gastiʀ}} > {{lang|non|gestr}}, but {{lang|mis|*staði}} > {{lang|non|*stað}}) or, regardless of syllable weight, if followed by consonantal {{lang|mis|i}} ({{lang|mis|*skunja}} > {{lang|non|skyn}}). The rule is not perfect, as some light syllables were still umlauted: {{lang|mis|*kuni}} > {{lang|non|kyn}}, {{lang|mis|*komiʀ}} > {{lang|non|kømr}}.
* In Old Norse, if the following syllable contains a remaining Proto-Norse {{lang|mis|i}}. For example, the root of the dative singular of ''u''-stems are i-mutated as the desinence contains a Proto-Norse {{lang|mis|i}}, but the dative singular of ''a''-stems is not, as their [[desinence]] stems from Proto-Norse {{lang|mis|ē}}.

I-mutation is ''not'' phonological if the vowel of a long syllable is i-mutated by a syncopated ''i''. I-mutation does not occur in short syllables.

{| class="wikitable"
|+ i-mutation
|-
! Original
! Mutated
! Example
|-
| {{lang|non|a}} || {{lang|non|e}} ({{lang|non|ę}}) || {{lang|non|fagr}} (fair) / {{lang|non|fegrstr}} (fairest)
|-
| {{lang|non|au}} || {{lang|non|ey}} || {{lang|non|lauss}} (loose) / {{lang|non|leysa}} (to loosen)
|-
| {{lang|non|á}} || {{lang|non|æ}} || {{lang|non|[[Æsir|Áss / Æsir]]}}
|-
| {{lang|non|o}} || {{lang|non|ø}} || {{lang|non|koma}} (to come) / {{lang|non|kømr}} (comes)
|-
| {{lang|non|ó}} || {{lang|non|œ}} || {{lang|non|róa}} (to row) / {{lang|non|rœr}} (rows)
|-
| {{lang|non|u}} || {{lang|non|y}} || {{lang|non|upp}} (up) / {{lang|non|yppa}} (to lift up)
|-
| {{lang|non|ú}} || rowspan="2" | {{lang|non|ý}} || {{lang|non|fúll}} (foul) / {{lang|non|fýla}} (filth)
|-
| {{lang|non|jú}} || {{lang|non|ljúga}} (to lie) / {{lang|non|lýgr}} (lies)
|-
| {{lang|non|ǫ}} || {{lang|non|ø}} || {{lang|non|sǫkk}} (sank) / {{lang|non|søkkva}} (to sink)
|}