The current geographical distribution of natively spoken Slavic languages includes the Balkans, Central and Eastern Europe, and all the way from Western Siberia to the Russian Far East.

[4][5][page needed][6] All Slavic languages have fusional morphology and, with a partial exception of Bulgarian and Macedonian, they have fully developed inflection-based conjugation and declension.

[7] Modern Bulgarian differs from other Slavic languages, because it almost completely lost declension, it developed definite articles from demonstrative pronouns (similar to "the" from "this" in English), and it formed indicative and renarrative tenses for verbs.

[8] Since the interwar period, scholars have conventionally divided Slavic languages, on the basis of geographical and genealogical principle, and with the use of the extralinguistic feature of script, into three main branches, that is, East, South, and West (from the vantage of linguistic features alone, there are only two branches of the Slavic languages, namely North and South).

[12] [13] [14] [15] [16] [17] [18] At the same time, recent studies of mutual intelligibility between Slavic languages revealed, that their traditional three-branch division does not withstand quantitative scrutiny.

During the Proto-Balto-Slavic period a number of exclusive isoglosses in phonology, morphology, lexis, and syntax developed, which makes Slavic and Baltic the closest related of all the Indo-European branches.

The secession of the Balto-Slavic dialect ancestral to Proto-Slavic is estimated on archaeological and glottochronological criteria to have occurred sometime in the period 1500–1000 BCE.

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.

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).

It was built using qualitative 110-word Swadesh lists that were compiled according to the standards of the Global Lexicostatistical Database project[27] and processed using modern phylogenetic algorithms.

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[28] and already not being monolithic.

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.

[40][page needed] 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.

[42] The following is a summary of the main changes from Proto-Indo-European (PIE) leading up to the Common Slavic (CS) period immediately following the Proto-Slavic language (PS).

As late as the 10th century AD, the entire Slavic-speaking area still functioned as a single, dialectally differentiated language, termed Common Slavic.

However, as a result of the loss of certain formerly present vowels (the weak yers), the modern Slavic languages allow quite complex clusters, as in the Russian word взблеск [vzblʲesk] ("flash").

Also present in many Slavic languages are clusters rarely found cross-linguistically, as in Russian ртуть [rtutʲ] ("mercury") or Polish mchu [mxu] ("moss", gen.

The word for "mercury" with the initial rt- cluster, for example, is also found in the other East and West Slavic languages, although Slovak retains an epenthetic vowel (ortuť).

An area of great difference among Slavic languages is that of prosody (i.e. syllabic distinctions such as vowel length, accent, and tone).

This consisted of phonemic vowel length and a free, mobile pitch accent: The modern languages vary greatly in the extent to which they preserve this system.

[47] The following is a very brief selection of cognates in basic vocabulary across the Slavic language family, which may serve to give an idea of the sound changes involved.

This is potentially because Slavic tribes crossed and partially settled the territories inhabited by ancient Illyrians and Vlachs on their way to the Balkans.

The Nordic languages also have torg/torv (market place) from Old Russian tъrgъ (trŭgŭ) or Polish targ,[48] humle (hops),[49] räka/reke/reje (shrimp, prawn),[50] and, via Middle Low German tolk (interpreter) from Old Slavic tlŭkŭ,[51] and pråm/pram (barge) from West Slavonic pramŭ.

[59][a] Owing to the medieval fur trade with Northern Russia, Pan-European loans from Russian include such familiar words as sable.