This page presents condensed reference-style information on Thai consonant clusters. A lesson-oriented approach to this material is available here.

In her indispensible layperson's text Reading and Writing Thai¹, Marie-Hélène Brown characterizes any instance of a Thai consonant cluster (อักษรควบ  /akL saawnR khuaapF/) as belonging to one of three types:

Brown's treatment derives from a native Thai approach to grammar which seems to recognize the same essential classification.² Each type will be discussed in more detail below. But first, some general observations on tones and orthography.

Tone determination

In general, for all clusters, the tone of the syllable is calculated based on the consonant class of the first consonant in the cluster; the tone marker (if any) is nevertheless placed above the second consonant in the group.

In fact, this very rule neatly accounts for the operation of the อักษรนำ  /akL saawnR nahmM/, or “silent” leading consonants, ออ นำ  /aawM nahmM/ and หอ นำ  /haawR nahmM/.

Most Type III(b) "non-conforming" clusters (clusters which internally invoke inherent sub-syllable /‑a/) use a sonorant second consonant and thus will follow the general rule as stated. However, the rule does not apply when the second consonant in the cluster is not a sonorant. The completely stated rule is as follows:

Here are some examples. In the preferred view, all of these represent a single orthographic syllable whose initial consonant cluster contains a half-pronounced sub-syllable.

Inherent /‑aaw/ probably shouldn't be considered a cluster. This inherent syllable is significant enough that its initial consonant does not bleed over, affecting subsequent tone calculations.

Clusters which invoke inherent /‑a/ or /‑aaw/ can never use a tone mark.

Orthography

With all types of consonant clusters, preposed vowels are placed before the entire cluster, and superscripted and underscripted vowels are placed with respect to the second consonant in the cluster. As mentioned above, where a tone mark is permitted, it, if any, is also placed above the second consonant in the cluster.

Sometimes the พินทุ  /phinM thooH/ symbol, a small dot below a consonant which carries no vowel sound, is used in dictionaries and other language-specific materials. For more information on the "Phinthu" character, please refer to the section on special symbols, where you'll also find usage examples.

Type I - True Clusters

Thai grammar identifies as true clusters, or อักษรควบแท้  /akL saawnR khuaapF thaaeH/, those cluster permutations where the first consonant is one of { ก, ข, ค, ต, ป, ผ, พ } and the second consonant is one of the three sonorants { ร, ล, ว }. Both consonants contribute equally to the pronounced sound of the cluster.

ว as the second consonant deserves special mention since it most often functions as a diphthong. A discussion of the diphthong usage of ว can be found on the vowels page. In this section we'll focus on its rarer usage as a true cluster, and we therefore dispense with Brown's possibly inadvertent inclusion of ปว-, ผว-, and พว-. I am also not able to find any instances of ผร-.

The special ligature ฤ can also act as the second consonant of a true cluster.

In addition to these cases, I have identified loanword usage which seems to imply additional clusters. One may argue that Thais do not pronounce the following words as shown, but the intention of the Thai spellings—and their de facto usage—are not in doubt. Consequently, our dictionary entry for each of these takes care to note that our transcription may possibly be rogue.

It's also possible that some Thais, perhaps those who have greater experience with the loanword languages, may pronounce such words differently than those without such experience.

Type II - False Clusters

Cononant clusters where the second consonant is a silent ร are called false clusters, or อักษรควบไม่แท้  /akL saawnR khuaapF maiF thaaeH/.

Type III - 'Leading Consonant' Clusters

a. Tone-Shifting 'Leading Consonant' Clusters

หอ นำ and ออ นำ refer to methods of accessing the rising and low tones which are not normally available with a sonorant initial by prepending a silent high-class consonant ห or อ, respectively so that the high-class tone rules are activated.

b. Non-conforming 'Leading Consonant' Clusters
If the two consonants in a cluster cannot be formed into a true consonant cluster, then they do not conform. The cluster will be called "non-conforming." They cluster is spoken only by the insertion of a sub-syllable /-a/ which does not affect the overall tone calculation for the orthographic syallable³. No tone mark may be used.

c. Inherent /-oh-/ Doesn't Belong in this Discussion
Brown includes inherent /‑oh-/ in her discussion of clusters but I feel that it doesn't belong here. It is a full-fledged vowel which links an initial consonant or consonant cluster to a final consonant or consonant cluster. There may be some technical basis for its inclusion according to the strictest definition of a cluster as "any two consonants written without a vowel," (Kumchai) but it seems more important to draw a distinction between it and sub-syllable /-a/.

In any case, here is a nutshell presentation: If the two consonants in the cluster belong to the same syllable, then inherent /‑oh-/ is invoked.

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Notes:
^1. Unfortunately, the book is out-of-print: Reading and Writing Thai, Marie-Hélène Brown, 1993. Bangkok, Editions Duang Kamol. ISBN 974 210 4506
^2. Where Brown's system differs from native Thai practice—in particular as advanced by Kumchai—we shall endeavor to hew to the latter. For example, Brown includes leading-H and leading-AAW in group II.
^4. Inherent /‑a/ can also appear at the end of a word—an extreme example being the word ณ  /naH/—but we are discussing only consonant clusters in this article.

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This article by Glenn Slayden
December 24, 2007
updated January 22, 2008