Around 93 million people speak Kra-Dai languages, 60% of whom speak Thai.Ethnologue lists 95 languages in the family, with 62 of these being in the Tai branch.
The high diversity of Kra-Dai languages in southern China points to the origin of the Kra-Dai language family in southern China. The Tai branch moved south into Southeast Asia only around 1000 AD.
Genetic and linguistic analysis show great homogeneity between Kra-Dai speaking people in Thailand.
The name "Kra-Dai" was proposed by Weera Ostapirat (2000), as Kra and Dai are the reconstructed autonyms of the Kra and Tai branches respectively. "Kra-Dai" has since been used by the majority of specialists working on Southeast Asian linguistics, including Norquest (2007), Pittayaporn (2009),Baxter & Sagart (2014), and Enfield & Comrie (2015).
The name "Tai-Kadai" is used in many references, as well as Ethnologue and Glottolog, but Ostapirat (2000) and others suggest that it is problematic and confusing, preferring the name "Kra-Dai" instead. "Tai-Kadai" comes from an obsolete bifurcation of the family into two branches, Tai and Kadai, which had first been proposed by Paul K. Benedict (1942). In 1942, Benedict placed three Kra languages (Gelao, Laqua (Qabiao) and Lachi) together with Hlai in a group that he called "Kadai", from ka, meaning "person" in Gelao and Laqua (Qabiao), and Dai, a form of a Hlai autonym. Benedict's (1942) "Kadai" group was based on his observation that Kra and Hlai languages have Austronesian-like numerals. However, this classification is now universally rejected as obsolete after Ostapirat (2000) demonstrated the coherence of the Kra branch, which does not subgroup with the Hlai branch as Benedict (1942) had proposed. "Kadai" is sometimes used to refer to the entire Kra-Dai family, including by Solnit (1988). Adding to the confusion, some other references restrict the usage of "Kadai" to only the Kra branch of the family.
This classification is used by Ethnologue, though by 2009 Lakkia was made a third branch of Kam-Tai and Biao was moved into Kam-Sui.
Ostapirat (2005); Norquest (2007)
Weera Ostapirat (2005:108) suggests the possibility of Kra and Kam-Sui being grouped together as Northern Kra-Dai, and Hlai with Tai as Southern Kra-Dai. Norquest (2007) has further updated this classification to include Lakkia and Be. Norquest notes that Lakkia shares some similarities with Kam-Sui, while Be shares some similarities with Tai. Norquest (2007:15) notes that Be shares various similarities with Northern Tai languages in particular. Following Ostapirat, Norquest adopts the name Kra-Dai for the family as a whole. The following tree of Kra-Dai is from Norquest (2007:16).
Additionally, Norquest (2007) also proposes a reconstruction for Proto-Southern Kra-Dai.
The Kra-Dai languages were formerly considered to be part of the Sino-Tibetan family, partly because they contain large numbers of words that are similar to Sino-Tibetan languages. However, these words are seldom found in all branches of the family and do not include basic vocabulary, indicating that they are old loan words.
Outside China, the Kra-Dai languages are now classified as an independent family.
In China, they are called Zhuang-Dong languages and are generally included, along with the Hmong-Mien languages, in the Sino-Tibetan family. It is still a matter of discussion among Chinese scholars whether Kra languages such as Gelao, Qabiao and Lachi can be included in Zhuang-Dong, since they lack the Sino-Tibetan similarities that are used to include other Zhuang-Dong languages in Sino-Tibetan.
Several scholars have presented suggestive evidence that Kra-Dai is related to or a branch of the Austronesian language family. There are a number of possible cognates in the core vocabulary displaying regular sound correspondences. Among proponents, there is yet no agreement as to whether they are a sister group to Austronesian in a family called Austro-Tai, a back-migration from Taiwan to the mainland, or a later migration from the Philippines to Hainan during the Austronesian expansion.
The inclusion of Japanese in the Austro-Tai family, as proposed by Paul K. Benedict in the late 20th century, is not supported by the current proponents of the Austro-Tai hypothesis.
Kosaka (2002) argued specifically for a Miao-Dai family. He argues that there is much evidence for a genetic relation between Hmong-Mien and Kra-Dai languages. He further suggests that similarities between Kra-Dai and Austronesian are because of later areal contact in coastal areas of eastern and southeastern China or an older ancestral relation (Proto-Eastasian).
Vovin (2014) proposed that the location of the JaponicUrheimat (linguistic homeland) is in Southern China. Vovin argues for typological evidence that Proto-Japanese may have been a monosyllabic, SVO syntax and isolating language, which are also characteristic of Tai-Kadai languages. According to him, these common features are however not due to a genetic relationship, but rather the result of intense contact.
No full reconstruction of Proto-Kra-Dai has been published to date, although tentative reconstructions of many Proto-Kra-Dai roots have been attempted from time to time. Some Proto-Kra-Dai forms have been reconstructed by Benedict (1975) and Wu (2002). A reconstruction of Proto-Kam-Tai (i.e., a proposed grouping that contains all of Kra-Dai without Kra, Hlai, and Jiamao) has also been undertaken by Liang & Zhang (1996).
Weera Ostapirat (2018a) reconstructs disyllabic forms for Proto-Kra-Dai, rather than sesquisyllabic or purely monosyllabic forms. His Proto-Kra-Dai reconstructions also contains the finals */-c/ and */-l/. Ostapirat (2018b:113) lists the following of his own Proto-Kra-Dai reconstructions.
*/K-/: either /k-/ or /q-/
*/C-/: unspecified consonant
*/T-/ and */N-/ are distinct from */t-/ and */n-/.
^Hammarström, Harald; Forkel, Robert; Haspelmath, Martin, eds. (2017). "Tai-Kadai". Glottolog 3.0. Jena, Germany: Max Planck Institute for the Science of Human History.
^Diller, Anthony, Jerry Edmondson, Yongxian Luo. (2008). The Tai-Kadai Languages. London [etc.]: Routledge. ISBN978-0-7007-1457-5
^ abSolnit, David B. 1988. "The position of Lakkia within Kadai." In Comparative Kadai: Linguistic studies beyond Tai, Jerold A. Edmondson and David B. Solnit (eds.). pages 219-238. Summer Institute of Linguistics Publications in Linguistics 86. Dallas: Summer Institute of Linguistics and the University of Texas at Arlington.
^ abEdmondson, Jerold A. and David B. Solnit, editors. 1988. Comparative Kadai: Linguistic studies beyond Tai. Summer Institute of Linguistics and the University of Texas at Arlington Publications in Linguistics, 86. Dallas: Summer Institute of Linguistics and the University of Texas at Arlington. vii, 374 p.
^Edmondson, Jerold A. and David B. Solnit, editors. 1997. Comparative Kadai: the Tai branch. Summer Institute of Linguistics and the University of Texas at Arlington Publications in Linguistics, 124. Dallas: Summer Institute of Linguistics and the University of Texas at Arlington. vi, 382 p.
^ abOstapirat, Weera. (2005). "Kra-Dai and Austronesian: Notes on phonological correspondences and vocabulary distribution", pp. 107-131 in Sagart, Laurent, Blench, Roger & Sanchez-Mazas, Alicia (eds.), The Peopling of East Asia: Putting Together Archaeology, Linguistics and Genetics. London/New York: Routledge-Curzon.
^Luo, Yongxian. 2008. Sino-Tai and Tai-Kadai: Another look. In Anthony V. N. Diller and Jerold A. Edmondson and Yongxian Luo (eds.), The Tai-Kadai Languages, 9-28. London & New York: Routledge.
Edmondson, J. A., & Solnit, D. B. (eds.) (1988). Comparative Kadai: linguistic studies beyond Tai. Summer Institute of Linguistics publications in linguistics, no. 86. Arlington, TX: Summer Institute of Linguistics. ISBN0-88312-066-6
Ostapirat, Weera. (2000). "Proto-Kra." Linguistics of the Tibeto-Burman Area23 (1): 1-251.
Somsonge Burusphat, & Sinnott, M. (1998). Kam-Tai oral literatures: collaborative research project between. Salaya Nakhon Pathom, Thailand: Institute of Language and Culture for Rural Development, Mahidol University. ISBN974-661-450-9