Proto-Slavic language

Proto-Slavic is the unattested, reconstructed proto-language of all Slavic languages. It represents Slavic speech approximately from the 2nd millennium BC through the 6th century AD. As with most other proto-languages, no attested writings have been found; scholars have reconstructed the language by applying the comparative method to all the attested Slavic languages and by taking into account other Indo-European languages.
Rapid development of Slavic speech occurred during the Proto-Slavic period, coinciding with the massive expansion of the Slavic-speaking area. Dialectal differentiation occurred early on during this period, but overall linguistic unity and mutual intelligibility continued for several centuries, into the 10th century or later. During this period, many sound changes diffused across the entire area, often uniformly. This makes it inconvenient to maintain the traditional definition of a proto-language as the latest reconstructable common ancestor of a language group, with no dialectal differentiation. Instead, Slavicists typically handle the entire period of dialectally differentiated linguistic unity as Common Slavic.
One can divide the Proto-Slavic/Common Slavic time of linguistic unity roughly into three periods:

an early period with little or no dialectal variation
a middle period of slight-to-moderate dialectal variation
a late period of significant variation

Authorities differ as to which periods should be included in Proto-Slavic and in Common Slavic. The language described in this article generally reflects the middle period, usually termed Late Proto-Slavic and often dated to around the 7th to 8th centuries. This language remains largely unattested, but a late-period variant, representing the late 9th-century dialect spoken around Thessaloniki in Macedonia, is attested in Old Church Slavonic manuscripts.

Introduction

Proto-Slavic is descended from the Proto-Balto-Slavic branch of the Proto-Indo-European language family, which is also the ancestor of the Baltic languages, e.g. Lithuanian and Latvian. Proto-Slavic gradually evolved into the various Slavic languages during the latter half of the first millennium AD, concurrent with the explosive growth of the Slavic-speaking area. There is no scholarly consensus concerning either the number of stages involved in the development of the language or the terms used to describe them.
One division is made up of three periods:

Early Proto-Slavic
Middle Proto-Slavic
Late Proto-Slavic

Another division is made up of four periods:

Pre-Slavic : A long, stable period of gradual development. The most significant phonological developments during this period involved the prosodic system, e.g. tonal and other register distinctions on syllables.
Early Common Slavic or simply Early Slavic : The early, uniform stage of Common Slavic, but also the beginning of a longer period of rapid phonological change. As there are no dialectal distinctions reconstructible from this period or earlier, this is the period for which a single common ancestor can be reconstructed.
Middle Common Slavic : The stage with the earliest identifiable dialectal distinctions. Rapid phonological change continued, alongside the massive expansion of the Slavic-speaking area. Although some dialectal variation did exist, most sound changes were still uniform and consistent in their application. By the end of this stage, the vowel and consonant phonemes of the language were largely the same as those still found in the modern languages. For this reason, reconstructed "Proto-Slavic" forms commonly found in scholarly works and etymological dictionaries normally correspond to this period.
Late Common Slavic : The last stage in which the whole Slavic-speaking area still functioned as a single language, with sound changes normally propagating throughout the entire area, although often with significant dialectal variation in the details.

This article considers primarily Middle Common Slavic, noting when there is slight dialectal variation. It also covers Late Common Slavic when there are significant developments that are shared identically among all Slavic languages.

Notation

Vowel notation

Two different and conflicting systems for denoting vowels are commonly in use in Indo-European and Balto-Slavic linguistics on the one hand, and Slavic linguistics on the other. In the first, vowel length is consistently distinguished with a macron above the letter, while in the latter it is not clearly indicated. The following table explains these differences:

Vowel	IE/B-S	Slavic
Short close front vowel	i	ĭ or ь
Short close back vowel	u	ŭ or ъ
Short open front vowel	e	e
Short open back vowel	a	o
Long close front vowel	ī	i
Long close back vowel	ū	y
Long open front vowel	ē	ě
Long open back vowel	ā	a

For consistency, all discussions of words in Early Slavic and before use the common Balto-Slavic notation of vowels. Discussions of Middle and Late Common Slavic, as well as later dialects, use the Slavic notation.

Other vowel and consonant diacritics

The caron on consonants is used in this article to denote the consonants that result from iotation and the Slavic first palatalization. This use is based on the Czech alphabet, and is shared by most Slavic languages and linguistic explanations about Slavic.
The acute accent on the consonant indicates a special, more frontal "hissing" sound. The acute is used in several other Slavic languages to denote a similar "frontal" quality to a consonant.
The ogonek, indicates vowel nasalization.
Prosodic notation

For Middle and Late Common Slavic, the following marks are used to indicate tone and length distinctions on vowels, based on the standard notation in Serbo-Croatian:

Acute accent : A long rising accent, originating from the Balto-Slavic "acute" accent. This occurred in the Middle Common Slavic period and earlier.
Grave accent : A short rising accent. It occurred from Late Common Slavic onwards, and developed from the shortening of the original acute tone.
Inverted breve : A long falling accent, originating from the Balto-Slavic "circumflex" accent. In Late Common Slavic, originally short vowels were lengthened in monosyllables under some circumstances, and are also written with this mark. This secondary circumflex occurs only on the original short vowels e, o, ь, ъ in an open syllable.
Double grave accent : A short falling accent. It corresponds to the Balto-Slavic "short" accent. All short vowels that were not followed by a sonorant consonant originally carried this accent, until some were lengthened.
Tilde : Usually a long rising accent. This indicates the Late Common Slavic "neoacute" accent, which was usually long, but short when occurring on some syllables types in certain languages. It resulted from retraction of the accent under certain circumstances, often when the Middle Common Slavic accent fell on a word-final final yer.
Macron : A long vowel with no distinctive tone. In Middle Common Slavic, vowel length was an implicit part of the vowel, so this is usually redundant for Middle Common Slavic words. However, it became distinctive in Late Common Slavic after several shortenings and lengthenings had occurred.
Other prosodic diacritics

There are multiple competing systems used to indicate prosody in different Balto-Slavic languages. The most important for this article are:

Three-way system of Proto-Slavic, Proto-Balto-Slavic, modern Lithuanian: Acute tone, circumflex tone or, short accent.
Four-way Serbo-Croatian system, also used in Slovenian and often in Slavic reconstructions: long rising, short rising, long falling, short falling. In the Chakavian dialect and other archaic dialects, the long rising accent is notated with a tilde, indicating its normal origin in the Late Common Slavic neoacute accent.
Length only, as in Czech and Slovak: long, short.
Stress only, as in Ukrainian, Russian and Bulgarian: stressed, unstressed.
History

Phonology

The following is an overview of the phonemes that are reconstructible for Middle Common Slavic.

Vowels

Middle Common Slavic had the following vowel system :
The columns marked "central" and "back" may alternatively be interpreted as "back unrounded" and "back rounded" respectively, but rounding of back vowels was distinctive only between the vowels *y and *u. The other back vowels had optional non-distinctive rounding. The vowels described as "short" and "long" were simultaneously distinguished by length and quality in Middle Common Slavic, although some authors prefer the terms "lax" and "tense" instead. Many modern Slavic languages have since lost all length distinctions.
Vowel length evolved as follows:

In the Early Slavic period, length was the primary distinction.
In the Middle Common Slavic period, all long/short vowel pairs also assumed distinct qualities, as indicated above.
During the Late Common Slavic period, various lengthenings and shortenings occurred, creating new long counterparts of originally short vowels, and short counterparts of originally long vowels. The short close vowels *ь/ĭ and *ъ/ŭ were either lost or lowered to mid vowels, leaving the originally long high vowels *i, *y and *u with non-distinctive length. As a result, vowel quality became the primary distinction among the vowels, while length became conditioned by accent and other properties and was not a lexical property inherent in each vowel.

In below, additional distinctions are made in the reconstructed vowels:

The distinction between *ě₁ and *ě₂ is based on etymology and they have different effects on a preceding consonant: *ě₁ triggers the first palatalization and then becomes *a, while *ě₂ triggers the second palatalization and does not change.
*ę̇ represents the phoneme that must be reconstructed as the outcome of pre-Slavic *uN, *ūN after a palatal consonant. This vowel has a different outcome from "regular" *ę in many languages: it denasalises to *ě in West and East Slavic, but merges with *ę in South Slavic. It is explained in more detail at.