Cœdès transliteration of Thai

The transliteration system referred to as Cœdès system is a reversible transliteration for Thai and Khmer, developed by Georges Cœdès and published in table form by his student Uraisi Varasarin.

This system is used in scholarly research. It tends to be favoured over the Royal Thai General System of Transcription—the official scheme promulgated by the Royal Thai Institute—because the latter is not reversible, as it underrepresents vowel quality and quantity.

G. Cœdès's transliteration system inherits some transliteration habits for scripts of Indian origin, such as the use of ṅ for the velar nasal, and the use of macron. It also reflects typographical convenience on a typewriter, such as the use of underlining.

Tones
The Thai script was devised at a stage when the language contrasted three tones. This required two marks, one of the three tones being left unmarked. These were supplemented by two other tonal marks. G. Cœdès did not propose a standardized way to transliterate all four tone marks. For a transliteration system that aims at exhaustivity, it seemed useful to have a system that covers all five types of tones, including explicit marking for the absence of tone mark. The following proposal was put forward by Krisda Tan Sirijunto and Alexis Michaud in 2015.