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Consonant Clusters

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:
I.True clusters
(sound as a
merged phoneme)
กล- /gl-/
พร- /phr-/
ตร- /dtr-/
พรวน   /phruaanM/
ตรวจ   /dtruaatL/
II.False clusters
(sound as a
single consonant)
ทร- /s-/
ทร- /t-/
-ทร /-t/
สร- /s-/
จร- /j-/
ทราบ   /saapF/
โทร   /tho:hM/
สมุทร   /saL mootL/
เสร็จ   /setL/
จริง   /jingM/
III.'Leading consonant' clusters
a.syllables with
หอ นำ or
ออ นำ

+ sonorant
+ sonorant

หนู   /nuuR/
อยู่   /yuuL/
b."non-conforming" clusters[any other initial/
final consonant pair]
กบ   /gohpL/
นคร   /naH khaawnM/
ขนม   /khaL nohmR/
แขนง   /khaL naaengR/
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.
ปลูก   /bpluukL/   -   Low tone determined by mid-class consonant
กล้อง   /glaawngF/   -   Falling tone determined by , yet tone mark appears above
In fact, this very rule neatly accounts for the operation of the อักษรนำ  /akL saawnR namM/, or “silent” leading consonants, ออ นำ  /aawM namM/ and หอ นำ  /haawR namM/.
Examples of หอ นำ  /haawR namM/
หมา   /maaR/, หลอด   /laawtL/, บุหรี่   /booL reeL/, หน่วง  /nuaangL/, หนวก   /nuaakL/, หญิง   /yingR/, หน่อย   /naawyL/, หนู   /nuuR/, หมด   /mohtL/, หมวก   /muaakL/, ไหม  /maiR/, ไหม้   /maiF/, เหงา  /ngaoR/, etc.
Examples of ออ นำ  /aawM namM/
อยู่   /yuuL/, อย่า   /yaaL/, อย่าง   /yaangL/, and อยาก   /yaakL/
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:
Clustered Consonant Tone Rule (full version):
In syllables with initial consonant clusters, the overall lexical tone is determined by the consonant class of:
• the first consonant in the cluster, if the second consonant is a sonorant;
• the second consonant in the cluster, if the second consonant is not a sonorant.
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.
With a sonorant second consonant, we observe tone carry-forward from first consonant:
สนุก   /saL nookL/   -   Second consonant of cluster is sonorant, so the Low tone of this syllable determined by high-class consonant

With non-sonorant second consonat, there is no tone carry-forward and the second consonant prevails:
แสดง   /saL daaengM/   -   Second consonant of cluster is non-sonorant (mid-class)
เกษียณ   /gaL siianR/   -   Second consonant of cluster is non-sonrant (high-class)
เฉพาะ   /chaL phawH/   -   Second consonant of cluster is non-sonorant (low-class)
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.
ไฉน  /chaL naiR/
แขนง   /khaL naaengR/


With all types of consonant clusters, preposed vowels are placed before the entire cluster, and superscripted and subscripted 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.
โปรด   /bpro:htL/Preposed vowel is placed before the cluster
เปล่า   /bplaaoL/Cluster with preposed vowel and tone mark
พริ้ม   /phrimH/Tone mark and superscripted vowel placed above the second consonant
เสมอ   /saL muuhrR/Preposed vowel placed before the cluster even in Type III; tone is carried forward also
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 { , , , , , , } and the second consonant is one of the three sonorants { , , }. Both consonants contribute equally to the pronounced sound of the cluster.

as the second consonant deserves special mention since it most often functions as a diphthong. A discussion of the diphthong usage of 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-.
กร- กล- กว-เกรง   /graehngM/, เกล็น   /glenM/, กว่า   /gwaaL/
ขร- ขล- ขว-ขรึม   /khreumR/, ขลุ่ย  /khluyL/, ขวัญ   /khwanR/
คร- คล- คว-เครื่อง   /khreuuangF/, คลอง   /khlaawngM/, ความ   /khwaamM/
ตร-ตระกูล   /dtraL guunM/
ปร- ปล-เปรียบ   /bpriiapL/, ปลา   /bplaaM/
     ผล-ผลัด  /phlatL/
พร- พล-พระ   /phraH/, พลอย   /phlaawyM/
The special ligature 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.
บร-   -   เบรค   /braehkL/, บรั่นดี  /branL deeM/, บราซิล  /braaM sinM/
บล-   -   บลูเบอร์รี่   /bluuM buuhrM reeF/, เบลซ  /blaehsL/
ดร-   -   ดรากอน  /draaM gaawnM/, ไฮโดรเจน  /haiM dro:hM jaehnM/

Type II - False Clusters

Cononant clusters where the second consonant is a silent are called false clusters, or อักษรควบไม่แท้  /akL saawnR khuaapF maiF thaaeH/.
ทร-/s-/ทราบ   /saapF/
ทร-/t-/โทร   /tho:hM/
-ทร/-t/สมุทร   /saL mootL/
สร-/s-/สร้าง   /saangF/
ซร-/s-/ไซร้  /saiH/
จร-/j-/จริง   /jingM/

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 or , respectively so that the high-class tone rules are activated.
หง-/ng-/หง่อย   /ngaawyL/
หน-/n-/หนู   /nuuR/
หม-/m-/หมา   /maaR/
หย-/y-/หยุด   /yootL/
หร-/r-/หรือ   /reuuR/
หล-/l-/หลับ   /lapL/
หว-/w-/หวัง   /wangR/
อย/y-/อยู่   /yuuL/

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.
ขนม   /khaL nohmR/
มรกต   /maawM raH gohtL/   -   กร, ทร, ธร, มร, and หร sometimes yield /‑aaw/
สนุก   /saL nookL/
แขนง   /khaL naaengR/   -   note preposed vowel positioning

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.
กบ   /gohpL/
รส   /rohtH/
ผล   /phohnR/
ส่ง   /sohngL/   -   Tone mark may be used.

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   /naH/—but we are discussing only consonant clusters in this article.
This article by Glenn Slayden
December 24, 2007
updated January 22, 2008
Copyright © 2017 Portions copyright © by original authors, rights reserved, used by permission; Portions 17 USC §107.