Akanie emerged in Southern Russian dialects as a result of unstressed vowel reduction: the sound [о открытое], which represented /o/ after hard consonants, coincided with [a]. In the western group of Southern Russian dialects, unstressed [о£], which represented /ω/, merged with [у] in some words or remained as [о]. The difference between dissimilative and strong akanie arose as a result of the realization of the same phonetic model in the dialects with different rhythmical word structures. The Zhizda type of dissimilative jakanie, complicated by the assimilation of the pretonic vowel to the stressed vowel [е], generated the Sudzha, Shchigrovsk and Mosalsk types of jakanie. They can be defined as types of assimilative-dissimilative jakanie. Assimilative-dissimilative jakanie developed from strong jakanie; for this reason, it is more appropriate to regard its types as representatives of assimilative-strong jakanie.