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1. Introduction

This is one of the most important reference pages at thai-language.com. Students studying Thai often spend a great deal of time learning the Thai consonants, while the vowels may get only a cursory look. Maybe this is because, unlike the consonants, the Thai vowels are not organized into a well-known pattern, with accompanying acrophonic objects and children's rhymes.

The vowels of the Thai language can be intimidating at first, especially when students learn that there are sixteen different vowel symbols that combine into different patterns. But many of the combinations make sense once you get the hang of it and the system can be mastered with a little dedication.

In Thai phonology, there are nine basic vowel monophthongs. Each of these is pronounced with either a short or a long duration, giving a total of eighteen simple vowel sounds. We'll present these first, and then discuss the few diphthongs that Thai uses.

But first, please note that in English the terms short and long (when speaking of vowels) sometimes refer to a certain grouping of vowel qualities (a distinction more properly referred to by the terms lax and tense), whereas in our discussion we will be using the linguistic meanings, where "long" and "short" refer to the relative length of time for which the vowel is pronounced. This feature, vowel duration, is not contrastive in English; for example, you can say, "ball" quickly or draw out the vowel, "baaaaaaall", and—while it may sound strange—the word still has the same meaning. In Thai, you must use the correct duration, or you might not be understood. For more information on this, please check the vowel duration page.

In addition to having long and short forms, each basic vowel sound can appear in an open or closed syllable. This means simply whether the vowel finishes (i.e. completes) the sound (open) or there is a final consonant tacked on (closed).

2. Monophthongs

Now we can proceed to the table of basic vowel sounds. Each of the nine basic sounds is shown for all four possible combinations: short-closed, short-open, long-closed, and long-open. The second line of each sound shows an example Thai word for each case.

3. Diphthongs

Next we have diphthongs, which are vowels that are pronounced as a glide between two monophthongs. In Thai, the second vowel of a diphthong is always -ะ /a/. There are three diphthongs in Thai (Tingsabadh and Abramson 1993, Iwasaki 2005). If you see that some other books list many more diphthongs, then they are probably counting the live consonant endings /y/ and /w/ as diphthongs (or triphthongs). Here, we opt for the simpler analysis and then list the glide endings /y/ and /w/ separately below. This approach is simpler because the nine vowels and three diphthongs listed in these two tables form the complete set of vowel phonemes in Thai.

As mentioned above, we have now listed all of the vowel phonemes of Thai; all of the sounds below this point are variations on the vowel phonemes listed above. Another objective of this page, however, is to present a complete reference on the ways in which the vowels of Thai are written in Thai. For this, we need to continue on with a study of the glide endings and two special vowel symbols, because there are some special vowel symbols that haven't appeared yet, and because there are some unexpected ways of combining vowel graphemes.

4. Glide Endings

Five of the nine monophthongs and two of the three diphthongs can appear with the glide ending consonant /y/ (IPA: /j/), which sounds like the high, front vowel /Y/. The open/closed syllable distinction is not shown in this table because none of these combinations can accept a further final consonant. In our analysis of these as consonant glides, that makes sense, because these syllables are already "closed" with the glide consonant. And this treatment is further confirmed by the fact that, if you did want to think of these as additional diphthongs and triphthongs, you'd have to explain why they can't accept a final consonant: there's no sound such as /doyk/ in Thai.

The glide ending /w/ can be used with five of the nine monophthongs and with the diphthong /ia/. As with the glide ending /j/, note that some of the duration contrasts are not attested. By now, you have probably noticed that our phonemic transcription does not adhere to this treatment of glide endings. There are two reasons for this. The first is that the system was originally developed before I was aware of this simplification. Secondly, such a system has to accomodate equally the phonology of Thai and the phonology of the learner's English; it was originally designed with the singular goal of allowing a beginning student to approximate Thai phonemes, without consideration for capturing important phonological generalizations of Thai.

5. Miscellaneous Vowel Orthography

To complete our discussion of the vowel graphemes used when writing Thai, we list the last two symbols that haven't appeared. The first one combines the simple monophthong /a/ with a closing sonorant, the consonant /m/. We'll put this in the "closed" syllable column, since it can't accept yet another consonant. Finally, there are the "ligatures" shown in row 27, which combine the initial consonant /r/ with either /ɯ/ or /i/. They're relatively rare, and you can memorize a short list of common words in which they appear.