Proto-Turkic language

Proto-Turkic is the linguistic reconstruction of the common ancestor of the Turkic languages that was spoken by the Proto-Turks before their divergence into the various Turkic peoples. Proto-Turkic separated into Oghur (western) and Common Turkic (eastern) branches. Candidates for the proto-Turkic homeland range from western Central Asia to Manchuria, with most scholars agreeing that it lay in the eastern part of the Central Asian steppe, while one author has postulated that Proto-Turkic originated 2,500 years ago in East Asia.

The oldest records of a Turkic language, the Old Turkic Orkhon inscriptions of the 7th century Göktürk khaganate, already shows characteristics of Eastern Common Turkic. For a long time, the reconstruction of Proto-Turkic relied on comparisons of Old Turkic with early sources of the Western Common Turkic branches, such as Oghuz and Kypchak, as well as the Western Oghur proper (Bulgar, Chuvash, Khazar). Because early attestation of these non-easternmost languages is much more sparse, reconstruction of Proto-Turkic still rests fundamentally on the easternmost Old Turkic of the Göktürks, however it now also includes a more comprehensive analysis of all written and spoken forms of the language.

The Proto-Turkic language shows evidence of influence from several neighboring language groups, including Eastern Iranian, Tocharian, and Old Chinese.

Consonants
The consonant system had a two-way contrast of stop consonants (fortis vs. lenis), k, p, t vs. g, b, d. There was also an affricate consonant, ç; at least one sibilant s and sonorants m, n, ń, ŋ, r, l with a full series of nasal consonants. Some scholars additionally reconstruct the palatalized sounds ĺ and ŕ for the correspondence sets Oghuric /l/ ~ Common Turkic *š and Oghuric /r/ ~ Common Turkic *z. Most scholars, however, assume that these are the regular reflexes of Proto-Turkic *l and *r. Oghuric is thus sometimes referred to as Lir-Turkic and Common Turkic as Shaz-Turkic.

A glottochronological reconstruction based on analysis of isoglosses and Sinicisms points to the timing of the r/z split at around 56 BCE–48 CE. As Anna Dybo puts it, that may be associated with

"the historical situation that can be seen in the history of the Huns' division onto the Northern and Southern [groups]: the first separation and withdrawal of the Northern Huns to the west has occurred, as was stated above, in 56 BC,... the second split of the (Eastern) Huns into the northern and southern groups happened in 48 AD."

Dybo suggests that during that period, the Northern branch steadily migrated from Western Mongolia through Southern Xinjiang into the north's Dzungaria and then finally into Kazakhstan's Zhetysu until the 5th century.

There was no fortis-lenis contrast in word-initial position: the initial stops were always *b, *t, *k, the affricate was always *č (*ç) and the sibilant was always *s. In addition, the nasals and the liquids did not occur in that position either.

Like in many modern Turkic languages, the velars /k/, /g/, and possibly /ŋ/ seem to have had back and front allophones ( and, and ,  and ) according to their environments, with the velar allophones occurring in words with front vowels, and uvular allophones occurring in words with back vowels. The lenis stops /b/, /d/ and /g/~/ɢ/ may have tended towards fricatives intervocalically.

Vowels
Like most of its descendants, Proto-Turkic exhibited vowel harmony, distinguishing vowel qualities a, ï, o, u vs. ä, e, i, ö, ü, as well as two vowel quantities. Here, macrons represent long vowels. Some scholars (e.g. Gerhard Doerfer) additionally reconstruct a mid back unrounded *ë based on cognate sets with Chuvash, Tuvan and Yakut ï corresponding to a in all other Turkic languages, although these correspondences can also be explained as deriving from *a which underwent subsequent sound changes in those three languages. The phonemicity of the distinction between the two close unrounded vowels, i.e. front *i and back *ï, is also rejected by some.

Nouns
Plurals of nouns were formed using the suffix *-An, but it fell into disuse sometime before the split between Common Turkic and Oghuric. Common Turkic languages today use their respective forms of *-lAr, whereas Chuvash uses -сем, which descends from Proto-Turkic *sāyïn ("every"). Reconstructable possessive suffixes in Proto-Turkic includes 1SG *-m, 2SG *-ŋ, and 3SG *-(s)i, plurals of the possessors are formed by *-z in Common Turkic languages.

Verbs
The reconstructable suffixes for the verbs include: Proto-Turkic also involves derivation with grammatical voice suffixes, as in cooperative *körüš, middle *körün, passive *körül, and causative *körtkür.
 * Aorist: *-Vr
 * Past: *-dI
 * Negative suffix: *-mA
 * 1SG: *-m < *-män < *bän
 * 2SG: *-n < *sän
 * 3SG: *-∅ < *ï
 * 1PL: *-mïz/*-bïz < *bïz
 * 2PL: *-sïz < *sïz