Middle Mongol or Middle Mongolian was a Mongolic koiné language spoken in the Mongol Empire. Originating from Genghis Khan's home region of northeastern Mongolia, it diversified into several Mongolic languages after the collapse of the empire. In comparison to Modern Mongolian, it is known to have had no long vowels, different vowel harmony and verbal systems and a slightly different case system.
Middle Mongol is close to Proto-Mongolic, the ancestor language of the modern Mongolic languages, which would to set at the time when Genghis Khan united a number of tribes under his command and formed the Mongol clan federation. The term "Middle Mongol" is somewhat misleading, as what would generally by language naming rules be termed "Old Mongolian" in this terminology is actually Proto-Mongolic. The existence of another ("old") Mongol clan federation in Mongolia during the 12th century is historical, but there is no language material from this period. The Khitan language seems to share a common ancestor with Proto-Mongolic, thus is further remote. According to Vovin (2018), the Ruanruan language of the Rouran Khaganate was a Mongolic language and close but not identical to Middle Mongolian.
The temporal delimitation of Middle Mongol causes some problems as shown in definitions ranging from the 13th until the early 15th or until the late 16th century. This discrepancy is mainly due to the fact that there are very few documents written in Mongolian language to be found between the early 15th and late 16th century. It is not clear whether these two delimitations constitute conscious decisions about the classification of e.g. a small text from 1453 with less than 120 words or whether the vaster definition is just intended to fill up the time gap for which little proper evidence is available.
Middle Mongol survived in a number of scripts, namely notably Phagspa (decrees during the Yuan Dynasty), Arabic (dictionaries), Chinese, Mongolian script and a few western scripts. Usually, the Stele of Yisüngge (ru) is considered to be its first surviving monument. It is a sports report written in Mongolian writing that was already fairly conventionalized then and most often dated at the verge of 1224 and 1225. However, Igor de Rachewiltz argues that it is unlikely that the stele was erected at the place where it was found in the year of the event it describes, suggesting that it is more likely to have been erected about a quarter of a century later, when Yisüngge had gained more substantial political power. If so, the earliest surviving Mongolian monument would be an edict of Töregene of 1240 and the oldest surviving text arguably the Secret History of the Mongols, a document that must originally have been written in Mongolian script arguably in 1252, but which only survives in an edited version as a textbook for learning Mongolian from the Ming period, thus reflecting the pronunciation of Middle Mongol from the second half of the 14th century.
The term "Middle Mongol" is problematic insofar as there is no body of texts that is commonly called "Old Mongol". While a revision of this terminology for the early period of Mongolian has been attempted, the lack of a thorough and linguistically-based periodization of Mongolian up to now has constituted a problem for any such attempts. The related term "Preclassical Mongolian" is applied to Middle Mongol documents in Mongolian script that show some distinct linguistic peculiarities.
Middle Mongol had the consonant phonemes /p, m, tʰ, t, s, n, l, r, t͡ʃʰ, t͡ʃ, j, kʰ, k, h/ and the vowel phonemes /i, e, y, ø, a, u, o/. The main difference to older approaches is that ⟨γ⟩ is identified with /h/ and /ɡ/ (sometimes as [p] before /u/ and /y/), so that *pʰ for Proto-Mongolic cannot be reconstructed from internal evidence that used to be based solely on word-initial /h/ and the then rather incomplete data from Monguor.
Middle Mongol is an agglutinating language that makes nearly exclusive use of suffixes. The word order is subject–object–predicate if the subject is a noun and also object–predicate–subject if it is a pronoun. Middle Mongol rather freely allows for predicate–object, which is due to language contact. There are nine cases, the nominative being unmarked. The verbal suffixes can be divided into finite suffixes, participles and converbal suffixes. Some of the finite suffixes inflect for subject number and sex. Adjectives precede their modificatum and agree with it in number.
Middle Mongol exhibits a passive construction that is peculiar to it and maybe Buryat as well, but is not present in the other dialects or in the other Mongolic languages. While it might also have fulfilled the function to foreground the patient, it usually seems to mark actions which either affect the subject directly or indirectly affect it in a harmful way.
In §131, Belgütei is negatively affected by an unknown actor. In §112, the addressee is the passive subject. While it is possible for the speech content to be passive subject, it is far less frequent. In §178, the referent of the subject is directly affected, but syntactically, the affected noun phrase is marked with the reflexive-possessive suffix (that on its own can resemble the accusative case in other contexts). In §163, it is not the referent of the subject noun phrase, but people related to it that are directly affected to the distress of the subject. The agent may be marked by the dative (-a and -da, but in contrast to Classical Mongolian never -dur) or the nominative:
In both of these examples, the verb stems to which the passive subject is suffixed are intransitive. Passive suffixes get suffixed to phrases, not verbal stems, e.g.:
In modern Mongolian, neither the passivization of ir- nor the suffixing of passive suffixes to phrases are possible, so the modern translation of §200 runs:
Next to the passive, there is also a causative that is, however, less notable. Subjects of intransitive verbs of clauses that are causativized get accusative marking (as in §79), while former subjects of transitive verbs get marked with dative or instrumental case (as in §188 and §31). In contrast to the passive suffix, the causative suffix doesn't attach to a phrase, but to single verbs (as long as they denote different actions):
Next to these morphemes, Middle Mongol also had suffixes to express reciprocal and cooperative meaning, namely -ldu- ~ -lda- and -lča-. On the other hand, while the plurative/distributive -čaγa- is common to modern Mongolic languages, it is not attested in Middle Mongol.