Romance languages
Unstressed vowels

There was more variability in the result of the unstressed vowels. Originally in Proto-Romance, the same nine vowels developed in unstressed as stressed syllables, and in Sardinian, they coalesced into the same five vowels in the same way.

In Italo-Western Romance, however, vowels in unstressed syllables were significantly different from stressed vowels, with yet a third outcome for final unstressed syllables. In non-final unstressed syllables, the seven-vowel system of stressed syllables developed, but then the low-mid vowels /ɛ ɔ/ merged into the high-mid vowels /e o/. This system is still preserved, largely or completely, in all of the conservative Romance languages (e.g. Italian, Spanish, Portuguese, Catalan).

In final unstressed syllables, results were somewhat complex. One of the more difficult issues is the development of final short -u, which appears to have been raised to /u/ rather than lowered to /o/, as happened in all other syllables. However, it is possible that in reality, final /u/ comes from long * -ū < -um, where original final -m caused vowel lengthening as well as nasalization. Evidence of this comes from Rhaeto-Romance, in particular Sursilvan, which preserves reflexes of both final -us and -um, and where the latter, but not the former, triggers metaphony. This suggests the development -us > /ʊs/ > /os/, but -um > /ũː/ > /u/.

The original five-vowel system in final unstressed syllables was preserved as-is in some of the more conservative central Italian languages, but in most languages there was further coalescence:

Various later changes happened in individual languages, e.g.:
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