Vowel reduction

A well-researched type of reduction is that of the neutralization of acoustic distinctions in unstressed vowels, which occurs in many languages.

[3] Sound duration is a common factor in reduction: In fast speech, vowels are reduced due to physical limitations of the articulatory organs, e.g., the tongue cannot move to a prototypical position fast or completely enough to produce a full-quality vowel (compare with clipping).

Stress-related vowel reduction is a principal factor in the development of Indo-European ablaut, as well as other changes reconstructed by historical linguistics.

Some languages, such as Finnish, Hindi, and classical Spanish, are claimed to lack vowel reduction.

[4] At the other end of the spectrum, Mexican Spanish is characterized by the reduction or loss of the unstressed vowels, mainly when they are in contact with the sound /s/.

Many Germanic languages, in their early stages, reduced the number of vowels that could occur in unstressed syllables, without (or before) clearly showing centralisation.

Proto-Germanic and its early descendant Gothic still allowed more or less the full complement of vowels and diphthongs to appear in unstressed syllables, except notably short /e/, which merged with /i/.

In Old Norse, likewise, only three vowels were written in unstressed syllables: a, i and u (their exact phonetic quality is unknown).

Vulgar Latin, represented here as the ancestor of the Italo-Western languages, had seven vowels in stressed syllables (/a, ɛ, e, i, ɔ, o, u/).

Some Romance languages, like Spanish and Romanian, lack vowel reduction altogether [citation needed].

Some regional varieties of the language, influenced by local vernaculars, do not distinguish open and closed e and o even in stressed syllables.

Unlike Neapolitan, Catalan and Portuguese, Sicilian incorporates this vowel reduction into its orthography.

The reduction [ɛ] > [ɪ] is prevalent in the eastern dialects of the language and is not considered formally correct.

Both vowels underwent reduction and were eventually deleted in certain positions in a word in the early Slavic languages, which began in the late dialects of Proto-Slavic.

In general, short vowels in Irish are all reduced to schwa ([ə]) in unstressed syllables, but there are some exceptions.

[7] Also in Munster Irish, an unstressed short vowel is not reduced to schwa if the following syllable contains a stressed /iː/ or /uː/: ealaí /aˈl̪ˠiː/ ('art'), bailiú /bˠaˈlʲuː/ ('gather').

[8] In Ulster Irish, long vowels in unstressed syllables are shortened but are not reduced to schwa: cailín /ˈkalʲinʲ/ ('girl'), galún /ˈɡalˠunˠ/ ('gallon').