On the origin of the instrumental case marker in the Manchu-Tungusic languages

One of these is the instrumental case marker, likely derived from the proto-language form *-gī. The reflexes of this reconstructed affix can be found in Jurchen and modern Manchu-Tungusic languages (-gi, -i, -ǯī, -ǯi, - č, -t). The sporadic palatalization of g before i occurred in the Manchu-Tungusic proto-language and its descendants. In Jurchen, which written documents date back to the 12th–15th centuries, the marker of the instrumental case was -gi. In Manchu, the instrumental case marker is identical to the genitive case marker -i. The author supposes that the former goes back to *-gī (> -gi > *-γi > *-ji > -i), whereas the latter derives from the proto-language form *-(j)i ~ -ni. Notably, the instrumental case marker has been preserved in its original form in at least one Manchu word: əmgi ‘together՚ (< *əmu-gi one-INSTR, cf. Ukrainian раз-ом one-INSTR ‘together՚). The author suggests that the affix *-gī originated from the word *gī ~ *-g͜ia ~ *guѢa ‘the other of two > side՚. The meaning ‘the other of two > side՚ is close to the meaning ‘opposite՚, which was one of the meanings of the Old English wið (it corresponds to the modern preposition with). Apparently, in the Manchu-Tungusic proto-language the case marker *-gī had originally the comitative meaning, which quite naturally developed from the meaning ‘the other of two > side՚. It is noteworthy that the comitative meaning is characteristic of modern instrumental case markers in several Manchu-Tungusic languages.