Jers refer to two vowel phonemes of the late Proto-Slavic and old Slavic languages, namely back jer (/ъ/) and front jer (/ь/). In phonetic transcription, the symbols ъ and ь taken from the Cyrillic alphabet are used. The jer phonemes are called jerˈˈ (ъ) and jerˈ (ь) by the names of the Glagolitic and Cyrillic jer letters (OCS jerъ and jerь) that symbolized /ъ/ and /ь/ in Old Church Slavic writing. Late PSl *ъ, *ь originated from the early PSl *ŭ, ĭ as a result of lowering. Later, the jer phonemes underwent the so-called jer shift, when in some positions (“weak”), jers…