The Southwestern Tai, Southwestern Thai or Thai languages are a branch of the Tai languages of Southeast Asia. Its languages include Siamese (Central Thai), Lanna, Lao, Shan and others. Classification The internal classification of the Southwestern Tai dialects is still not well agreed on. Chamberlain (1975) Chamberlain (1975) divides Southwestern Tai into 4 branches. Chamberlain based his classification on the following phonological patterns. (Note: For an explanation of the notation system for Tai tones, see Proto-Tai language#Tones.) /p/ vs. /ph/ tone *A column split/merger pattern tone *BCD columns split/merger patterns B-DL tonal coalescence Proto-Southwestern Tai Branch with distinguishing innovation: /p/ Branch with distinguishing innovation: *A 1-23-4 Tse Fang, a variety of Tai Nuea spoken at Zhefang (遮放镇) in Mangshi, Yunnan, China Tai Mao, a variety of Tai Nuea spoken at Nam Hkam, Shan State, Myanmar Muang Ka, a variety of Tai Nuea spoken at Muang Ka in Muang Baw, Yunnan, China Branch with distinguishing innovation: *ABCD 123-4; B=DL Black Tai spoken at Sơn La, Vietnam Red Tai White Tai Lue, a composite of varieties from many locations in several countries Shan spoken at Kengtung ca. 1930s Yuan, a composite of varieties spoken in the capital towns of Chiang Rai, Phrae, Nan, Lampang, and Chiang Mai, Thailand Ahom Branch with distinguishing innovation: /ph/ (*A 1-23-4) Branch with distinguishing innovation: *BCD 123-4 Siamese Phu Tai Lao Neua spoken at "Nam Tha" (perhaps referring to Luang Namtha, Laos) Phuan spoken at Ban Mi, Lopburi, Thailand and Pak Seng Branch with distinguishing innovation: *BCD 1-23-4; B≠DL Lao Southern Thai The Tai Muong Vat of Yen Chau, Vietnam is a PH-type language like Lao, even though it is geographically surrounded by Black Tai (Theraphan 2003; Chamberlain 1984). Edmondson & Solnit (1997) Edmondson & Solnit (1997) divide the Southwestern Tai dialects into two major subgroups. According to this classification, Dehong Tai and Khamti are the first languages to have split off from the Southwestern Tai branch. Northern: Tai Nua = Shan-Tayok (Chinese Shan), Khamti Southern: Burman Shan ("Shan proper"), all other Southwestern Tai A transition zone between the Northern and Southern groups occurs among the Tai languages (including Tai Mau) around the Burma-China border region of Mangshi, Namhkam, and Mu-se near Ruili. This bipartite division of Southwestern Tai is argued for by Edward Robinson in his paper "Features of Proto-Nüa-Khamti" (1994). The following features set off the Nüa-Khamti group from all the other Southwestern Tai dialects.