Slavic languages
Differentiation

The Proto-Slavic language existed until around AD 500. By the 7th century, it had broken apart into large dialectal zones.

There are no reliable hypotheses about the nature of the subsequent breakups of West and South Slavic. East Slavic is generally thought to converge to one Old East Slavic language, which existed until at least the 12th century.

Linguistic differentiation was accelerated by the dispersion of the Slavic peoples over a large territory, which in Central Europe exceeded the current extent of Slavic-speaking majorities. Written documents of the 9th, 10th, and 11th centuries already display some local linguistic features. For example, the Freising manuscripts show a language that contains some phonetic and lexical elements peculiar to Slovene dialects (e.g. rhotacism, the word krilatec). The Freising manuscripts are the first Latin-script continuous text in a Slavic language.

The migration of Slavic speakers into the Balkans in the declining centuries of the Byzantine Empire expanded the area of Slavic speech, but the pre-existing writing (notably Greek) survived in this area. The arrival of the Hungarians in Pannonia in the 9th century interposed non-Slavic speakers between South and West Slavs. Frankish conquests completed the geographical separation between these two groups, also severing the connection between Slavs in Moravia and Lower Austria (Moravians) and those in present-day Styria, Carinthia, East Tyrol in Austria, and in the provinces of modern Slovenia, where the ancestors of the Slovenes settled during first colonisation.

In September 2015, Alexei Kassian and Anna Dybo published, as a part of interdisciplinary study of Slavic ethnogenesis, a lexicostatistical classification of Slavic languages. It was built using qualitative 110-word Swadesh lists that were compiled according to the standards of the Global Lexicostatistical Database project and processed using modern phylogenetic algorithms.

The resulting dated tree complies with the traditional expert views on the Slavic group structure. Kassian-Dybo's tree suggests that Proto-Slavic first diverged into three branches: Eastern, Western and Southern. The Proto-Slavic break-up is dated to around 100 A.D., which correlates with the archaeological assessment of Slavic population in the early 1st millennium A.D. being spread on a large territory and already not being monolithic. Then, in the 5th and 6th centuries A.D., these three Slavic branches almost simultaneously divided into sub-branches, which corresponds to the fast spread of the Slavs through Eastern Europe and the Balkans during the second half of the 1st millennium A.D. (the so-called Slavicization of Europe).

The Slovenian language was excluded from the analysis, as both Ljubljana koine and Literary Slovenian show mixed lexical features of Southern and Western Slavic languages (which could possibly indicate the Western Slavic origin of Slovenian, which for a long time was being influenced on the part of the neighboring Serbo-Croatian dialects), and the quality Swadesh lists were not yet collected for Slovenian dialects. Because of scarcity or unreliability of data, the study also did not cover the so-called Old Novgordian dialect, the Polabian language and some other Slavic lects.

The above Kassian-Dybo's research did not take into account the findings by Russian linguist Andrey Zaliznyak who stated that, until the 14th or 15th century, major language differences were not between the regions occupied by modern Belarus, Russia and Ukraine, but rather between the north-west (around modern Velikiy Novgorod and Pskov) and the center (around modern Kyiv, Suzdal, Rostov, Moscow as well as Belarus) of the East Slavic territories. The Old Novgorodian dialect of that time differed from the central East Slavic dialects as well as from all other Slavic languages much more than in later centuries. According to Zaliznyak, the Russian language developed as a convergence of that dialect and the central ones, whereas Ukrainian and Belarusian were continuation of development of the central dialects of East Slavs.

Also Russian linguist Sergey Nikolaev, analysing historical development of Slavic dialects' accent system, concluded that a number of other tribes in Kievan Rus came from different Slavic branches and spoke distant Slavic dialects.

Zaliznyak and Nikolaev's points mean that there was a convergence stage before the divergence or simultaneously, which was not taken into consideration by Kassian-Dybo's research.

Ukrainian linguists (Stepan Smal-Stotsky, Ivan Ohienko, George Shevelov, Yevhen Tymchenko, Vsevolod Hantsov, Olena Kurylo) deny the existence of a common Old East Slavic language at any time in the past. According to them, the dialects of East Slavic tribes evolved gradually from the common Proto-Slavic language without any intermediate stages.
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