Vowel reduction in Russian differs in the standard language and dialects, which differ from one another. Several ways of vowel reduction (and its absence) are distinguished.
Contents
There are five vowel phonemes in Standard Russian. Vowels tend to merge when they are unstressed. The vowels /a/ and /o/ have the same unstressed allophones for a number of dialects and reduce to an unclear schwa. Unstressed /e/ may become more central if it does not merge with /i/.
Other types of reduction are phonetic, such as that of high vowels (/i/ and /u/), which become near-close so игра́ть ('to play') is pronounced [ɪˈɡratʲ], and мужчи́на ('man') is pronounced [mʊˈɕːinə].
Russian orthography does not reflect vowel reduction, which can confuse foreign-language learners.
Back vowels
Other than in Northern Russian dialects as well as those of Kostroma and Vologda, Russian speakers have a strong tendency to merge unstressed /a/ and /o/, called akanye (аканье). It contrasts with okanye (оканье) pronunciations. It works in Standard Russian as follows:
Across certain word-final suffixes, the reductions do not completely apply. In certain suffixes, after palatalised consonants and /j/, /a/ and /o/ (which is written as ⟨е⟩) can be distinguished from /i/ and from each other: по́ле [ˈpolʲɪ] ('field' nominative singular neuter) is different from по́ля [ˈpolʲə] ('field' singular genitive), and the final sounds differ from the realisation of /i/ in that position.
There are a number of exceptions to the above comments regarding the akanye:
Front vowels
The main feature of front vowel reduction is ikanye (иканье), the merger of unstressed /e/ with /i/. Because /i/ has several allophones (depending on both stress and proximity to palatalised consonants), unstressed /e/ is pronounced as one of these allophones and not actually as the close front unrounded vowel. For example, семена́ ('seeds') is pronounced [sʲɪmʲɪˈna], цена́ ('price') [t͡sɨ̞ˈna].
In registers without the merger (yekanye or еканье), unstressed /e/ is more retracted. Even then, however, the distinction between unstressed /e/ and unstressed /i/ is most clearly heard in the syllable just before the stress. Thus, прида́ть ('to add to') contrasts with преда́ть ('to betray'). The two are pronounced [prʲɪˈdatʲ] and [prʲe̠ˈdatʲ] respectively. Yekanye pronunciation is coupled with a stronger tendency for both unstressed /a/ and /o/ to be pronounced the same as /i/.
Speakers may switch between the two types of pronunciation because of various factors, the most important factor likely being speed of pronunciation.
Yakanye
Yakanye (яканье) is the pronunciation of unstressed /e/ and /a/ following palatalised consonants preceding a stressed syllable as /a/ rather than /i/ (несли is pronounced [nʲasˈlʲi], not [nʲɪsˈlʲi]).
The non-standard rural pronunciation is observed in most Southern Russian dialects, as expressed in a Russian quip (with liberal yakanye):
The example also demonstrates other features of Southern dialects: palatalised final /t/ in the 3rd person forms of verbs, [ɣ] instead of [ɡ] and [w] instead of [u] (in some places) and [v], clear unstressed [a] in place of [ɐ] or [ə].
Spelling
Vowel reduction makes some words have spellings that contradict their etymology, such as паром (instead of пором that was standard spelling before Ushakov's dictionary), каравай (instead of коровай, the standard spelling until the reform of 1956), свидетель (instead of сведетель, with a long history).
In the closely related Belarusian language, words are often pronounced the same way as in Russian, but their reduced pronunciation is reflected directly in the spelling such as in the name of the country itself: Белоруссия vs. Беларусь ('white Rus') has the final unstressed vowel in the prefix бел[о|а]- ('white') spelled 'о' in Russian but 'а' in Belarusian.