Abstract This article proposes a new historical subgrouping of Old Tibetan dialects. It demonstrates that Tibetan dialects started to differentiate in late pre-historical times, shortly before the script introduction. The emergence of the first dialects is shown to have resulted from the military expansion of the Tibetan Empire. The reconstruction of the dialect formation supplements earlier insights by studying modern equivalents of Old Literary Tibetan ɣbras , the Proto-Tibetic form of which has been reconstructed as *mbras. In addition, comparing its cognates in other presumably closely related languages permitted the reconstruction of *mras to Proto-Bodic and, tentatively, *mrats to Proto-Trans-Himalayan.
Joanna Bialek (2026) studied this question.