Proto-Balto-Slavic

Proto-Balto-Slavic is a reconstructed proto-language descending from Proto-Indo-European (PIE). From Proto-Balto-Slavic, the later Balto-Slavic languages are thought to have developed, composed of sub-branches Baltic and Slavic, and including modern Latvian, Lithuanian, Polish, Ukrainian, Russian and Serbo-Croatian among others.

Like most other proto-languages, it is not attested by any surviving texts but has been reconstructed using the comparative method. There are several isoglosses that Baltic and Slavic languages share in phonology, morphology and accentology, which represent common innovation from Proto-Indo-European times and can be chronologically arranged.

Proto-Indo-European voiced aspirated stops lost their aspiration in Proto-Balto-Slavic. Stops were no longer distinguished between fortis and aspirated but were voiceless and voiced. However, several new palatal (postalveolar) consonants had developed: *ś and *ź from earlier palatovelar plosives and *š from *s as a result of the Ruki sound law.

Proto-Balto-Slavic preserved much of the late Proto-Indo-European vowel system. One noticeable difference between the two was the merging of earlier short /o/ and /a/ into /a/. Earlier syllabic sonorants in PIE had been converted into liquid diphthongs by inserting *i or *u before the sonorant in Proto-Balto-Slavic.

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