Kymna organizes its vowels based on a rounded/unrounded distinction. The most prominent change is u-mutation – it is triggered by u and causes vowels to gain roundness, as in Old Norse. But unlike Old Norse, it only affects the immediately preceding vowel (e.g. salis ’happiness’, salydzuma ’happy’). The changes are:
Posttonic vowels usually lose their roundness: o, y > a, i. This change is resisted when these vowels are preceded by dominant labials like m, v and stressed o, u: *plepswin > *lessyn > lessin ’baby’, but *tobor > tovor ’horse’. Hence also a > o in proximity to dominant labials: *kuQma > kūmo ’bear’.
The vowel u, on the other hand, rarely loses its roundness; and develops u > *[ʌ] > a if it does. In colloquial speech, it laxens in pronounciation posttonically, i.e. it is centralized to [ʉ].
Before m (and less commonly before n) one finds a > o and o > u. Sometimes e > i before nasals (*be-ma ta ’bleating one’ > vimata ’sheep’).
The Proto-Tallic i-diphthongs changed in the following way: *ai, *ei, *əi > ei, ei, ī with unstressed ei > e, while *oi, *ui were a source of the new vowel y. In Moluma, *ai becomes ae and is distinct from ei:
The Proto-Tallic u-diphthongs changed in the following way: *au, *ou, *eu, *əu, *iu > ou, ou, ëy, ū, ȳ, essentially undergoing u-mutation.
The schwa from the Proto-Tallic e-grade became e after dentals (the most common situation), a after velars, and i after labials. It had no influence on the preceding vowel as it is the case in Talmit and was subsequently lost after n: