Slavic second palatalization

The Slavic second palatalization is a Proto-Slavic sound change that manifested as a regressive palatalization of inherited Balto-Slavic velar consonants that occurred after the first and before the third Slavic palatalizations.

The second palatalization of velars is a direct consequence of the monophthongization of diphthongs, or more precisely, the change *aj > ē. While *kaj, *gaj and *xaj were in accordance with the principle of so-called intrasyllabic synharmony that operated during the Common Slavic period, the resulting *kē, *gē, and *xē defied the intrasyllabic synharmony since the velars ended up in front of the resulting front vowel ē, which defied Proto-Slavic phonotactical constraints.

This anomaly was resolved by palatalizing the velars, just as it was done during the first palatalization. However, the results of the second palatalization were different and not completely uniform across Slavic territory, indicating one of the first dialectal differences. Usually, this palatalization is described as gradual, with fronting to proper palatals occurring first and then (perhaps with those that were affected with the third palatalization) assibilation. Hence it is sometimes called sibilantization.

In addition, the same process operated before the new instances of *i deriving from *oj.

The inherited velars *k (< PIE *k, *kʷ) and *g (< PIE *g, *gʰ, *gʷ, *gʷʰ) change before the Proto-Slavic diphthong *aj/āj (< PIE *oy, *h₂ey/ay), which itself must have become *ē by the time the second palatalization started to occur:

Proto-Slavic velar fricative *x that was absent in PIE, and which arose primarily from PIE *s by means of RUKI law, from word-initial PIE #sk- as well as from Germanic and Iranian borrowings, changed in the same environment as:

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