The fifteen Katuic languages form a branch of the Austroasiatic languages spoken by about 1.3 million people in Southeast Asia. People who speak Katuic languages are called the Katuic peoples. Paul Sidwell is the leading specialist on the Katuic languages. He notes that Austroasiatic/Mon–Khmer languages are lexically more similar to Katuic and Bahnaric the closer they are geographically. He says this geographic similarity is independent of which branch of the family each language belongs to. He also says Katuic and Bahnaric do not have any shared innovations, so they do not form a single branch of the Austroasiatic family, but form separate branches.
In 1966, a lexicostatistical analysis of various Austroasiatic languages in Mainland Southeast Asia was performed by Summer Institute of Linguistics linguists David Thomas and Richard Phillips. This study resulted in the recognition of two distinct new subbranches of Austroasiatic, namely Katuic and Bahnaric (Sidwell 2009). Sidwell (2005) casts doubt on Diffloth's Vieto-Katuic hypothesis, saying that the evidence is ambiguous, and that it is not clear where Katuic belongs in the family. Sufficient data for use in the sub-classification of the Katuic languages only become available after the opening of Laos to foreign researchers in the 1990s.
The sub-classification of Katuic below was proposed by Sidwell (2005). Additionally, Sidwell (2009) analyzes the Katu branch as the most conservative subgroup of Katuic.
Gehrmann (2019) proposes the following classification of the Katuic languages.
Ethnologue also lists Kassang (the Tariang language), but that is a Bahnaric language (Sidwell 2003). Lê, et al. (2014:294) reports a Katu subgroup called Ba-hi living in mountainous areas of Phong Điền District, Vietnam, but Watson (1996:197) speaks of "Pacoh Pahi" as a Pacoh variety.
Kuy and Bru each have around half a million speakers, while the Ta’Oi cluster has around 200,000 speakers.
Reconstructions of Proto-Katuic, or its sub-branches, include:
Sidwell (2005) reconstructs the consonant inventory of proto-Katuic as follows:
This is identical to reconstructions of proto-Austroasiatic except for *ʄ, which is better preserved in the Katuic languages than in other branches of Austro-Asiatic, and which Sidwell believes was also present in Proto-Mon Khmer.
Paul Sidwell (2015:185-186) lists the following lexical innovations unique to Katuic that had replaced original Proto-Austroasiatic forms.
Sidwell (2015:173) lists the following lexical isoglosses shared between Katuic and Bahnaric.
|bark of tree||*ʔnɗɔh||*kɗuh|
|claw/nail||*knrias||*krʔniəh||cf. Khmer kiəh 'to scratch'|
|to stand up||*dɨk||*dɨk||may be borrowed from Chamic|
|tree/wood||*ʔalɔːŋ||*ʔlɔːŋ||cf. Proto-Khmuic *cʔɔːŋ|
|crossbow||*pnaɲ||*pnaɲ||cf. Old Mon pnaɲ 'army'|
Furthermore, Gerard Diffloth (1992) lists the words 'centipede', 'bone', 'to cough', 'to fart', 'to breathe', and 'blood' as isoglosses shared between Katuic and Vietic. A Vieto-Katuic connection has also been proposed by Alves (2005).