The preceding discussion argued that syllable structure changed in Slavic before the loss of weak jers and that intrasyllabic and intersyllabic reorganizations in Late Common Slavic (LCS) had a far more important role in its evolution than did the loss of jers. Not only did the reorganization of syllable structure produce major isoglosses in LCS, but it also had far-reaching implications for subsequent developments in the individual Slavic languages, both on the segmental and the prosodic level. Several new proposals were made with respect to the nature of phonological change in Common Slavic (CS).

The syllable structure changes that occurred in CS were the result of several constraints. The earliest innovation was the emergence of the Moraic Constraint. It resulted in the elimination of syllable-final obstruents and in the neutralization of length in diphthongs. A No Coda Constraint came into play later in CS. Historical accounts of the Slavic languages do not distinguish between the two, citing the “law of open syllables” as responsible for the loss of syllable-final consonants or a movement of the syllable boundary. By Late Common Slavic the high ranking of the No Coda Constraint was a regional phenomenon. The developments in (North) East LCS, for example, may be described as the interaction of two other constraints, one on maximal syllable weight and another on the moraicity of sonorant consonants without reference to the No Coda Constraint. (North) West Slavic, in fact, had syllable codas as an outcome of constraint interaction in that area.