Proto-Mongolic, the ancestor language of the modern Mongolic languages, is very close to Middle Mongol, the language spoken at the time of Genghis Khan and the Mongol Empire. Most features of modern Mongolic languages can thus be reconstructed from Middle Mongol. An exception would be the voice suffix like -caga- 'do together', which can be reconstructed from the modern languages but is not attested in Middle Mongol.
Proto-Mongolic, the ancestor language of the modern Mongolic languages, is very close to Middle Mongol, the language spoken at the time of Genghis Khan and the Mongol Empire. Most features of modern Mongolic languages can thus be reconstructed from Middle Mong,ol. An exception would be the voice suffix like -caga- 'do together' which can be reconstructed from the modern languages but is not attested in Middle Mongol.