[4] Some scholars, including Benedict (1975), have used Thai to refer to a wider (Tai) grouping and one sees designations like proto-Thai and Austro-Thai in earlier works.

[4] On the other hand, Gedney, Li and others have preferred to call the standard language of Thailand Siamese rather than Thai, perhaps to reduce potential Thai/Tai confusion, especially among English speakers not comfortable with making a word-initial unaspirated voiceless sound for Tai, which in any event might sound artificial or arcane to outsiders.

According to Michel Ferlus, the ethnonyms Tai/Thai (or Tay/Thay) would have evolved from the etymon *k(ə)ri: 'human being' through the following chain: kəri: > kəli: > kədi:/kədaj (-l- > -d- shift in tense sesquisyllables and probable diphthongization of -i: > -aj).

Michel Ferlus' work is based on some simple rules of phonetic change observable in the Sinosphere and studied for the most part by William H. Baxter (1992).

Citing the fact that both the Zhuang and Thai peoples have the same exonym for the Vietnamese, kɛɛuA1,[a] derived from the name of Jiaozhi in Vietnam, and that the indigenous Bai Yue were given family names by their northern rulers during the Northern and Southern dynasties, while the Thai didn't have family names into the 19th century, Jerold A. Edmondson of the University of Texas at Arlington posited that the split between Zhuang (a Central Tai language) and the Southwestern Tai languages happened no earlier than the founding of Jiaozhi in 112 BCE but no later than the 5th–6th century AD.

Ancient Chinese texts refer to non-Sinitic languages spoken across this substantial region and their speakers as "Yue".

One of the very few direct records of non-Sinitic speech in pre-Qin and Han times having been preserved so far is the "Song of the Yue Boatman" (Yueren Ge 越人歌), which was transcribed phonetically in Chinese characters in 528 BC, and found in the 善说 Shanshuo chapter of the Shuoyuan 说苑 or 'Garden of Persuasions'.

[10] Haudricourt emphasizes the specificity of Dioi (Zhuang) and proposes to make a two-way distinction between the following two sets.

Characteristics of the Dioi group pointed out by Haudricourt are Li Fang-Kuei divided Tai into three sister branches.

In Pittayaporn's preliminary classification system of the Tai languages, Central Tai is considered to be paraphyletic and is split up into multiple branches, with the Zhuang varieties of Chongzuo in southwestern Guangxi (especially in the Zuo River valley at the border to Vietnam) having the most internal diversity.