The fronting of back vowels after *j in Slavonic

Abstract In the field of Slavonic historical phonology, it has long been known that many of the Proto-Indo-European back vowels become front after *j in Late Common Slavonic (henceforth LCS). We call this sound change Vowel Fronting. Vowel Fronting plays an important role in the rise of one of the major characteristics of the Slavonic languages, namely, the distinction between hard and soft declensions. However, not all the back vowels become front after *j in LCS, and the exact conditions for the vowel fronting have not been found yet. Here we show that the fronting is a regular sound change. The presence or absence of the etymological syllable-final consonants, which are lost in LCS, plays a decisive role in Vowel Fronting. By assuming that Vowel Fronting occurred before syllable-final consonants are lost, we define Vowel Fronting as a sound law that occurs in the following four environments without any exception: (1) in final closed syllables, (2) in light syllables, (3) between two *j’s, and (4) when the nucleus is *y [ɨ].