Reduced Vowels

(also jers), the reduced vocalic phonemes in the old Slavic languages, which were designated by the letters ъ (back jer) and b (front jer).

Reduced vowels developed in Proto-Slavic as a result of the transformation of the Indo-European short close vowels *ῠ and *ῐ. In Proto-Slavic of a later era and in the old Slavic languages, front jer was an unrounded middle or high-middle front vowel, and back jer was a middle or high-middle back vowel, apparently rounded. Reduced vowels were in what is known as weak position at the end of a word, before a syllable with a full vowel, and before a syllable with a reduced vowel in strong position, as in stolъ (“throne,” “seat”; nom. and acc. sg., gen. pl.), sъna (“dream,” “sleep”; gen. sg., nom. and acc. dual), and žbnbcb (“reaper”; nom. sg., gen. pl.). They were in strong position before a syllable with a weak reduced vowel, in an initial stressed syllable, and, in Old Russian, before a liquid consonant, as in šbvbcb (“tailor”; nom. sg., gen. pl.), dъskǫ (“board”; acc. sg.), and vbrxъ (“top”; nom. and acc. sg., gen. pl.). Before a yod [j], back jer became [y̆] and front jer became [ῐ]; these vowels also could be in strong and weak positions.

In all the Slavic languages, the strong reduced vowels were changed to full vowels and the weak reduced vowels were lost.