Based on comparative studies by Ferlus (1982, 1992, 1997, 2001) and new studies in Muong languages by Phan (2012),Phan, John. 2012. "Mường is not a subgroup: Phonological evidence for a paraphyletic taxon in the Viet-Muong sub-family." In Mon-Khmer Studies, no. 40, pp. 1-18., 2012. Sidwell (2015)Sidwell, Paul. 2015. "Austroasiatic classification." In Jenny, Mathias and Paul Sidwell, eds (2015). The Handbook of Austroasiatic Languages, 144-220. Leiden: Brill. pointed out that Muong is a paraphyletic taxon and subgroups with Vietnamese. Sidwell's (2015) proposed internal classification for the Vietic languages is as follows.
