While the Thai language shares the same roots than Khmer, it does not belong to the same group. Indeed, it is part of the Tai branch of the Kra Dai group. Over half of its lexicon comes from Pali, Sanskrit, Mon and Old Khmer. Also, it is a tonal and analytic language, similar to Chinese.

Thai is close to other South West Tai dialects such as Lao and Shan (in Myanmar). As well as a couple of local dialects spoken from Laos to Nort Vietnam and South China. We estimate more than 45 million native and 65 total speakers.

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In fact, Thai is not a single language. Indeed, there are nearly 60 different Thai dialects in the country. Among them, Siamese is the main one in the country. Indeed, Siamese Thais make up about 40% of the total population and are the ones who run the country. As a result, they have imposed their language as the norm in the country. This is true at the highest level of the state and in media. Thus, the official Thai is indeed Siamese Thai.

As for the other Tai languages, they are not dialects but rather sister languages. Among the main ones are Isan, Muang and Pak Tai.

  • First, we find Isan, also called Lao Thai, in the north east of the country, with about 20 million speakers.
  • Second, 6 million speakers speak Muang, also called Yuan. The latter spread in the hilly areas of the North.
  • Third, 14 provinces in the South speak Pak Tai with about 5 million speakers.

The closest ones to Siamese Thai are:

  • Northern Thai, Thai Song and Phuan.
  • Some Tai languages in Vietnam such as Tai Daeng, Tai Dam, Tai Dón, Tai Hang Tong, Tày Tac and Thu Lao.

With them, Siamese forms the so-called Chiang Saeng branch of the Tai group. Actually, this name refers to a place in the Golden Triangle near Chiang Rai, North Thailand.

Also, with Nyaw and Phuthai, Lao and Isan form the Phu Thai sub group. As Isan and Lao are very close, there is a strong link across the border between the two countries. In contrast, there is no evidence of a continuum between Thai and Isan speakers, let alone Lao speakers.

Finally, Southern Thai is a separate language from both the Chiang Saeng and Lao Phuthai sub groups. Same thing for Yong, another Thai language.

Elite Translation Tai languages distribution


As all dialects, Thai has known various sound changes since 800 years. Of course, some of the main changes occurred during the evolution from Old Thai to modern Thai. And many others, mainly in consonants and tones, occured with the modern spelling.

Early Old Thai

Early Old Thai had velar fricatives /x ɣ/ as distinct phonemes. At some point in the history of Thai, a palatal nasal phoneme /ɲ/ also existed, coming from Proto-Tai. Also, the letter ญ yo ying allow to highlight a palatal nasal in words borrowed from Sanskrit and Pali. We pronounce it /j/ at the beginning and /n/ at the end of a syllable. Same case in modern Thai. Plus, most native Thai with words starting with /ɲ/. This suggests that /ɲ/ > /j/ in native words occurred in the pre literary period.

Thai comes from Proto Tai Kadai, which appeared in the Lower Yangtze valleys. Ancient Chinese texts refer to non Sinitic dialects spoken accross this region and their speakers as "Yue". Although those dialects do no longer exist, we found traces of them in unearthed script materials. As well as ancient Chinese historical texts and non-Han substrata in various South Chinese dialects.

As the most spoken language in the Tai Kadai group, people used Thai to clarify the origins of dialect(s) spoken in the ancient region of South China. The "Song of the Yue Boatman" is one of the very few direct records of non Sinitic speech in pre Qin and Han times, preserved so far. Linguists transcribed the latter in Chinese signs in 528 BC.

In the early 80's, the Zhuang linguist Wei Qingwen found out that the lexicon showed strong resemblance to modern Zhuang. Later, Zhengzhang Shangfang went deeper and used Thai script. This, since it dates from the 13th century and preserves archaisms with respect to modern pronunciation.

Elite Translation Old Thai script on stone in National Museum of Bangkok

Elite Translation Learn about the Vietnamese language Global distribition of VIetnamese speakers

Old Thai

Initially, Old Thai had a three-way tone distinction on "live syllables", with no possible distinction on "dead syllables". That is to say either /p/, /t/, /k/ or the glottal stop which closes syllables ending in a short vowel. Also, there was a two-way voiced vs. voiceless distinction among all fricative and sonorant consonants. And up to four-way among stops and affricates.

Voicing distinction losses and the concomitant tone split is the major change between old and modern Thai. This happened between about 1300 and 1600, at possible different times in different areas. All voiced voiceless pairs of consonants lost the voicing distinction.

However, in the process of these mergers, the former voice distinction transferred into a new set of tonal distinctions. In essence, every tone in Old Thai split into two new tones. This, first with a lower pitched tone refering to a syllable that formerly began with a voiced consonant. Second, with a higher pitched tone refering to a syllable that formerly began with a voiceless consonant.


Until the 13th century, Chinese influence was strong before the use of Chinese signs was abandoned and replaced by Sanskrit and Pali scripts. However, the Thai lexicon has kept many words from Middle Chinese.

After that, Sanskrit and Pāli made most lexicon. This is the case in Buddhism field. Then, Old Khmer has also contributed its share, mainly in regard to royal court terminology. Finally, from the 20th century, English lend its lexicon for scientific, technical, international, and other modern terms.


In order to transcribe the language tonal system, Thai uses an adapted alpha syllabary, derived from Khmer which derives itself from Pali.

On the one hand, there are 20 consonants, written with 44 letters, although two have fallen into disuse. On the other hand, there are 24 vowels, written with 13 letters and which include diphthongs and triphthongs.

Also, the tonal system varies according to the choice of consonants that we can divide into 3 groups. In addition, 4 accents are used to correct this system and to integrate foreign words that are not easy to transcribe.

As with Latin dialects, we write Thai from left to right. Also, there is no punctuation. And some words can be written stuck together like in German. Of course, there are no capital letters and the letters are not linked.

Plus, Modern Thai gets 9 pure vowels and 3 centering diphthongs, each of which can occur short or long. Except compound and foreign words, most words have only one syllable.


Note that there is no standard for transcribing Thai into the Latin script. Thus, written papers can have their own transcription system. This is one of the reasons why many Thai lessons encourage students to master the Thai script. However, the Royal Thai Institute has published the Royal General Thai Transcription System (RTGS). Administration use the latter more and more, for road signs mainly. Also, it does not consider the tone and length of the vowels. As a result, it is  not possible to rewrite in the Thai script from an RTGS transcription.

In order to solve that issue, an international standard for transliteration from the Thai to the Latin alphabet was published in 2003. Contrary to RTGS, the diacritical symbols in this system allow to highlight the tone and length of vowels. Thus, we can then switch from Latin to Thai. But we rarely use this system outside academia.


From the point of view of linguistic typology, Thai is an isolating language. In other words, all words are not variable. So, there are no articles, genres, plural or tenses. But some particles allow to mark the number, nouns and tenses.

Elite Translation Article Learn about the Thai language Thai transcription Consonants ans tonal system