Thai phonology

Initials
Thai distinguishes three voice-onset times among plosive and affricate consonants:
 * voiced
 * aspirated
 * tenuis (unvoiced, unaspirated)

Where English makes a distinction between voiced and aspirated, Thai distinguishes a third sound that is neither voiced nor aspirated, which occurs in English only as an allophone of , for example after an  as in the sound of the p in "spin". There is similarly an alveolar, , triplet in Thai. In the velar series there is a, pair and in the postalveolar series a ,  pair, but the language lacks the corresponding voiced sounds  and. (In loanwords from English, English and  are borrowed as the tenuis stops  and .)

In each cell below, the first line indicates International Phonetic Alphabet (IPA), the second indicates the Thai characters in initial position (several letters appearing in the same box have identical pronunciation).


 * ฃ and ฅ are no longer used. Thus, modern Thai is said to have 42 consonant letters.
 * Initial อ is silent and therefore considered as glottal plosive.

Finals
Although the overall 44 Thai consonant letters provide 21 sounds in case of initials, the case for finals is different. For finals, only eight sounds, as well as no sound, called mātrā (มาตรา) are used. To demonstrate, at the end of a syllable, บ and ด  are devoiced, becoming pronounced as  and  respectively. Additionally, all plosive sounds are unreleased. Hence, final, , and sounds are pronounced as , , and  respectively.

Of the consonant letters, excluding the disused ฃ and ฅ, six (ฉ ผ ฝ ห อ ฮ) cannot be used as a final and the other 36 are grouped as following.


 * * The glottal plosive appears at the end when no final follows a short vowel

Clusters
In Thai, each syllable in a word is considered separate from the others, so combinations of consonants from adjacent syllables are never recognised as a cluster. Thai has phonotactical constraints that define permissible syllable structure, consonant clusters, and vowel sequences. Original Thai vocabulary introduces only 11 combined consonantal patterns:
 * (กร), (กล),  (กว)
 * (ขร,คร), (ขล,คล),  (ขว,คว)
 * (ปร), (ปล)
 * (พร), (ผล,พล)
 * (ตร)

The number of clusters increases when a few more combinations are presented in loanwords such as (ทร) in อินทรา (, from Sanskrit indrā) or  (ฟร) in ฟรี (, from English free); however, it can be observed that Thai language supports only those in initial position, with either, , or  as the second consonant sound and not more than two sounds at a time.

Vowels
The basic vowels of the Thai language, from front to back and close to open, are given in the following table. The top entry in every cell is the symbol from the International Phonetic Alphabet, the second entry gives the spelling in the Thai alphabet, where a dash (–) indicates the position of the initial consonant after which the vowel is pronounced. A second dash indicates that a final consonant must follow.

The vowels each exist in long-short pairs: these are distinct phonemes forming unrelated words in Thai, but usually transliterated the same: เขา (khao) means "he" or "she", while ขาว (khao) means "white".

The long-short pairs are as follows:

The basic vowels can be combined into diphthongs. analyze those ending in high vocoids as underlyingly and. For purposes of determining tone, those marked with an asterisk are sometimes classified as long:

Additionally, there are three triphthongs, all of which are long:

For a guide to written vowels, see the Thai alphabet page.

Tones
There are five phonemic tones: mid, low, falling, high, and rising, sometimes referred to in older reference works as rectus, gravis, circumflexus, altus, and demissus, respectively. The table shows an example of both the phonemic tones and their phonetic realization, in the IPA.



The full complement of tones exists only in so-called "live syllables", those that end in a long vowel or a sonorant.

For "dead syllables", those that end in a plosive or in a short vowel, only three tonal distinctions are possible: low, high, and falling. Because syllables analyzed as ending in a short vowel may have a final glottal stop (especially in slower speech), all "dead syllables" are phonetically checked, and have the reduced tonal inventory characteristic of checked syllables. In native words that have been used for a very long time, only a two-way tonal distinction occurs: falling vs. low for syllables containing a long vowel, and high vs. low for syllables containing a short vowel (i.e. ending either in a short vowel + plosive, or in a short vowel alone).

Checked syllables
In some English loanwords, closed syllables with long vowel ending in an obstruent sound, have high tone, and closed syllables with short vowel ending in an obstruent sound have falling tone.