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Inside a Thai Syllable: Part II

Initial Consonant Clusters

In Part I of this article, we learned how to tease out the initial- and final consonants, and vowel symbols from simple Thai syllables, in order to pronounce them. You might have been surprised how easy it was!

We can expand upon the twenty-one initial consonant sounds that are available with simple initial consonants by beginning to consider two consonants appearing together: consonant clusters.1 In Thai, they’re called อักษรควบ  /akL saawnR khuaapF/. We’ll be looking at three types of consonant cluster, a method which is inspired by native Thai grammatical sensibility. We’ll learn to think about words like a Thai!

I. - True Consonant Clusters

We’ll start with the simplest type of cluster, the true consonant cluster (อักษรควบแท้  /akL saawnR khuaapF thaaeH/). A cluster is ‘true’ if both of the consonant sounds are ‘blended’ or ‘melded’ together so that, as you speak the overall sound, both letters contribute equally. Examples in English are: quick, which starts with a clustered /kw-/ sound, or price, which starts with /pr-/.

In the phonology of a given language, only certain consonants can be combined in this way. Try saying the nonsense word, ‘gkow;’ unless you’re a Klingon, you probably can’t, without sounding a vowel between the /g/ and /k/. Most English speakers can’t blend together the /g/ and /k/ sounds without inserting a vowel in-between, a process called epenthetic anaptyxis that we’ll come back to later on. Let’s look at the true clusters that Thai phonology permits:
In a true consonant cluster, the first consonant must be one of { , , , , , , } and the second consonant must be one of the three sonorants { , , }.
Here’s the first example:
กว่า    ([suffix used for comparisons] than; more; -er)
This sounds like /gwaaL/; you probably know the word already from your conversation studies. Notice how, when you say it, your mouth forms the initial consonant cluster into a single blended sound, which all happens before the vowel sound. This word has no final consonant.

Our approach to understanding syllables reduces the number of rules you must learn. There’s one simple rule that’s very important, though. Although we’ll refine it a bit later, the initial version of the rule covers most cases. You’ll want to commit it to memory.
  Clustered Consonant Tone Rule:
In syllables with initial consonant clusters, the spoken tone is determined by the consonant class of the first consonant in the cluster.2
In the case of กว่า , this means that we use , a mid-class consonant, along with the presence of the ไม้เอก   /maaiH aehkL/ tone mark to determine that the spoken tone must be low.

This is a good chance to point out some orthographic details which apply to all clusters: the tone mark for a cluster, if any, is written over the second consonant in the cluster, as shown in the previous example. Superposed and subposed vowels are also written over the second consonant. And as we’ll see next, any preposed vowel element is placed before the entire cluster. This word uses true cluster /คร-/:
ใคร่    (to desire; wish; prefer)
Just as we did when there was a single initial consonant instead of an initial consonant cluster, the preposed vowel is placed in front of the whole shebang. Before continuing, study the example words listed under ‘Type I - True Clusters’ on the Consonant Clusters reference page.

II. - False Consonant Clusters

We’ve just seen that in true consonant clusters, the two consonants were blended, equally participating in the formation of the syllable-initial sound. Next, we’ll examine consonant clusters in which the second consonant is and it’s completely silent. This type of cluster is called อักษรควบไม่แท้  /akL saawnR khuaapF maiF thaaeH/, or a false consonant cluster.
In a false consonant cluster, the first consonant is one of { , , , , , }, and the second consonant, which must be , is silent.3
For example:
สร้าง    (to build; construct; create; establish; to cause)
It’s pronounced /saangF/. Let’s run through the tone calculation for this one. Since we always use the first consonant of the cluster to determine the tone (according to the rule), we note that the first consonant, , is a high-class consonant. When the second tone mark, ไม้โท   /maaiH tho:hM/, is present, as it is here, we know that the syllable must be spoken with a falling tone.

In some cases, the presence of the silent influences the pronunciation of the syllable. In Thai, this is called ออกเสียงแปรไปเป็นเสียงตัวอื่น  /aawkL siiangR bpraaeM bpaiM bpenM siiangR dtuaaM euunL/.
ทราบ    ([polite] to know a fact or piece of information)
Here, thanks to the influence of silent , ทร is pronounced as /s-/, not /th-/ as you might expect. The correct pronunciation of the word is /saapF/.

Interestingly, this particular consonant cluster can also operate the same way as a final consonant cluster. In the next example, concentrate on the final consonant box and don’t worry about the ‘enepenthetic’ cluster in the initial consonant position (we’ll be discussing epenthetic clusters below). The important thing to see at this point is that the false consonant cluster ทร is acting as a /-t/ sound, so the following is pronounced /saL mootL/:
สมุทร    (ocean; sea)
Preposed vowels in false consonant clusters are still handled in the same way as discussed above. For more practice, take a look at this one, which uses the false cluster /ซร-/:
ไซร้    ([a particle used at the end of a conditional clause for emphasis or rhetoric effect] certainly)
This word is pronounced /saiH/. Just as we did with true clusters, the preposed vowel is placed in front of the whole cluster, so it’s the first grapheme in the syllable. This means that, when reading Thai text—which is all run together, without spaces between the words or syllables—the preposed vowels can help you recognize where syllables start.
Since preposed vowels can only occur at the beginning of a new syllable, they help you find the breaks between syllables and words.
You can find more examples of false clusters listed under ‘Type II’ on the Consonant Clusters reference page.

III. - ‘Leading Consonant’ Clusters

The final type of consonant cluster is a broadly-defined category. We’ve already looked at true consonant clusters and false consonant clusters. Any remaining cases of two consonants appearing together with the same vowel are called อักษรควบที่ใช้อักษรนำ  /akL saawnR khuaapF theeF chaiH akL saawnR namM/, or leading consonant clusters. This remainder bin covers a lot of territory, so we’ll break down a few distinct patterns. All are very common in Thai, so you won’t want to skip this section.

a. - Tone-shifting ‘Leading Consonant’ Clusters

A large number of Thai words use an initial consonant cluster in which the first consonant—which must be either or —is silent. If you’ve learned about these silent leading consonants before, you probably memorized a rule about how the tone is affected in such syllables. But now we’ll see that, with our one simple rule, we actually don’t have to introduce anything new to understand these clusters!
หนู     (mouse; mice; rat)
If you haven’t started studying the tone rules yet, you can just note that the in this cluster is silent, so we get the pronunciation /nuuR/. is called หอ นำ  /haawR namM/, or “leading H-” in this role.

But read on, and you’ll see that figuring the tone becomes simple when we remember the rule we stated above: the tone of the syllable is determined by the first consonant in the cluster. In this case, it’s the silent , a high-class consonant. This means that we get to use the high-class tone rules for a syllable which, from a pronunciation standpoint, starts with the low-class consonant ! The leading “provides access” to the rising and low spoken tones, which are normally not available to low-class consonants. In the case of หนู  , the tone is rising because of the long vowel and the open syllable.

“Leading H” (หอ นำ) can appear in a cluster when the second consonant is any one of the low class sonorant consonants { , , , , , , , , , }. The reason that it’s needed and its function here is to provide a method for changing the tone of these sonorant initial consonants, because unlike all of the other low-class consonants which have a high-class phonetic equivalent consonant, these would otherwise have no way to deliver the rising or low spoken tones.

In addition to หอ นำ, there are four words that use in exactly the same way—as a silent, leading consonant that ends up shifting the tone of the syllable. This use is called ออ นำ  /aawM namM/.
The four words that use ออ นำ:
อยู่   /yuuL/
อย่า   /yaaL/
อย่าง   /yaangL/
อยาก   /yaakL/

b. - Enepenthetic ‘Leading Consonant’ Clusters

So far, the distinction between orthographic syllables and phonetic syllables that we accentuated at the beginning of Part I has not seemed important. Each written syllable we’ve studied (except for /saL mootL/, which we glossed over) has signified a single spoken syllable. Now we’ll see that certain initial consonant clusters can seem to break this pattern.

If the clustered consonants can’t be blended (as in a true consonant cluster) or simplified (as in a false consonant cluster) then how can they be pronounced? We got a clue to the answer when we were looking at the Klingon-language example in Part I. If you force yourself to speak consonants that won’t blend, you’ll find yourself inserting a hardly-perceptible vowel sound in-between them. This becomes an unwritten - sound (very short /-a/)—called an anaptyxix (or สวรภักดิ์  /saL waH raH phakH/ svarabhakti, to use the Sanskrit word)—pronounced as part of the consonant cluster.

Since the process of inserting the short vowel, which is called epenthesis, occurs within the cluster, we call such clusters enepenthetic. One Thai teacher suggested thinking of it as “one-quarter of a full vowel.” Here’s the first example:
สนาม    (field; park; lawn; playground; meadow; yard; turf; grassy field)
Even though we still think of this as a single written syllable, it’s pronounced /saL naamR/. The short vowel is encapsulated, or ‘nested’ fully within the orthographic syllable. The first, immediate benefit of thinking of it this way—as opposed to thinking of /saL/ as a separate, standalone syllable—is that your pronunciation of the overall syllable improves when you try to force the enepenthetic initial consonant cluster into sounding as a unit. Try it both ways; you’ll notice a difference. Now you’re speaking like a Thai!

An enepenthetic initial cluster can appear with an implied vowel:
ถนน    (road; boulevard; avenue; street)
I’m sure you know this word, /thaL nohnR/. It has no written vowels, but now we know how to break it down into an initial cluster which contains svarabhakti /-a/ and the unwritten vowel /-oh-/. The latter connects the initial cluster to the final consonant.

Now consider the tone of the overall syllable. As we’ve been discussing, we should think of this a single orthographic syllable. What would happen if we instead thought of ถนน  as two independent syllables, /thaL/ and /nohnR/? The tone of the first, having a high-class initial consonant () and being an open syllable with a short vowel, is low. So far, so good. But now wait, the second ‘syllable’ (นน) has a low-class initial consonant and a live ending; the tone should be mid!? This way of thinking breaks down.

Now, let’s zoom in on just the initial consonant box:

When we realize that the unwritten vowel (the svarabhakti) - is fully encapsulated within the consonant cluster, we can see that the initial consonant that’s exposed to the overall orthographic syllable is , a high-class consonant. That sub-syllable that we had to insert to make the cluster pronuncable isn’t perceptible enough to cancel the first consonant’s effect on the overall syllable (remember the rule?). Now, when we apply the tone rules, we come up with the correct spoken tone for the word, rising4.
In enepenthetic initial clusters (consonant clusters which incorporate a spoken svarabhakti -), the consonant class of the first consonant determines not only the consonant class of the cluster as a whole (as in other types of clusters), but also the tone of the spoken epenthetic sub-syllable which uses unwritten -.
Yikes? It’s not actually that complicated if you strip away the fancy terminology. To make sure you’ve got it, see if you can rephrase it in your own words. Try reading this well-known word: นคร . You’ll have to use much of what you’ve learned so far.

So, as we’ve seen with the other types of consonant clusters, the spoken tone of the overall syllable is still determined by the consonant class of the first consonant in the cluster (, in our example). So remember, keep the clustered consonants together, thinking of the cluster as a unit which contains the sub-syllable /ถะ/ within it.

Let’s take a moment to recognize the difference between the implied /-oh-/ vowel that we encountered earlier, and this implied /-a/. The former is a full-fledged vowel which can occupy the light-green triangle in our diagram, connecting an initial consonant to a final consonant. The latter is a sub-syllable (enepenthetic) sound which exists within a cluster and makes the pronunciation of the cluster possible. We should be sure to appreciate that they have little in common with each other except that neither is explicitly written.

c. - Preposed Vowels in Enepenthetic Clusters

We’ve seen how important it is to keep the two consonants in a cluster coupled together. But we haven’t even discussed what’s perhaps one of the most compelling reasons why. We’ll now reveal how your hard work so far will pay off, and how this method seamlessly handles what could otherwise be a confusing situation: using a vowel with a preposed element in a syllable with an enepenthetic initial consonant cluster.

Consider the word เฉลียง , which is pronounced /chaL liiangR/. If you try to build syllables in a linear fashion, by scanning the word from left-to-right, you’ll find yourself in a jumble. The first character, , is a preposed vowel which is part of the overall compound vowel. You’d have to ignore it for now. Next you’d encounter and recognize the ‘first syllable’ /chaL/. Now you’d recall the preposed vowel5, to perhaps construct the ‘second syllable’ เลียง, except for one problem: this syllable generates the wrong tone, mid. So you’d have to remember to perform ‘tone carrying’ from the first syllable to arrive at the correct tone, rising. Phew!

Now let’s do it the Thai way:
เฉลียง    (hall; corridor)
The power of this technique is that we don’t have to introduce anything new in order to handle this case. The vowel orthography is handled just like we saw with เตียง  earlier, the cluster (ฉล) is handled just like we saw with ถนน  earlier, and the tone comes out correctly, without any special rules.

Would you like to try another one? See if you can work it out on your own: เจริญ . Draw the diagram if you need to.

d. - Refining the clustered consonant tone rule

Here are some further details on calculating the tone of these syllables. I recommend skipping this section if you just want to learn the basics.

First, recall that the sonorant consonants are those low-class consonants to which you can hum a tune, namely { , , , , , , , , , }. They roughly correspond to the hummable English sounds { ng, n, m, y r, l, w }—try humming them. As you learn Thai words, you’ll notice that the second consonant in enepenthetic clusters is usually a sonorant. If, however, it’s not, then the tone of the overall syllable will be determined according to the class of that second consonant.

An intuitive explanation of this is that, in Thai phonotactics, non-sonorant second consonants are even harder to force into a cluster. Even epenthesis can’t really do the trick, so finally that sub-syllable breaks free and becomes a fully-fledged syllable.

Now we can state the full version of the clustered consonant tone rule:
  Clustered Consonant Tone Rule (full version):
In syllables with initial consonant clusters, the overall spoken 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 with mid-class second consonant: แสดง , เสบียง , เผอิญ , เผดียง (and presumably also เสด็จ  and เผด็จ  although the distinction makes no difference due to their dead consonant endings). Here are some examples with high-class second consonant: เกษียณ , เกษียร . And finally, here are two examples with a low-class, non-sonorant second consonant: เฉพาะ , เผชิญ

By the way, no cluster can be composed from two mid-class consonants.

IV - Other Clusters

a. Cluster /บร-/ Using Sub-syllable /เบาะ--/

We call clusters ‘enepenthetic’ when Thai phonotactics won’t permit the two clustered consonants to be merged together in their pronunciation. The minimum vowel sound /-a/ is inserted in order to ease the pronunciation, and the tone is still determined by the first consonant.

At the end of the previous section, however, we saw how this process is fragile, and the epenthetic syllable can break away if it becomes too ‘heavy.’ Another case where this can occur is with the cluster /บร-/, which appears with the vowel /บริ/ in many words. This syllable (not a valid word when standing alone) is pronounced /bawL riH/. For this example, we’ll use a two-syllable word, like so:
บริการ    (to serve, help, assist, support, service)
This word is pronounced /baawM riH gaanM/. Notice the second syllable uses the final /-aawn/ as discussed in Part I. But let’s focus on the first syllable by zooming in on its initial consonant cluster.

Just as we saw with non-sonorant second consonants in the previous section, here the epenthetic /aaw/ is too substantial to stay confined within its the consonant cluster /บร-/. Consequently, it gets promoted to a full spoken syllable which determines its own tone. It might be best to think of this case as implying the stand-alone syllables /เบาะ/ and /ริ/, since thinking of it as a cluster doesn’t offer any advantage. The spoken tone of the second “syllable” /ริ/ will always will always be high.

b. Cluster รร

Some Thai grammarians consider รร to be an instance of false consonant cluster. There are two special ways that รร can be pronounced:
  • เป็นตัวสกดด้วยกัน (รร acting as vowel /-a/) {ตรรค, ธรรม, อรรถ, etc.}
  • การันต์ตัวหลัง (รร acting as /-an/).
Because both of these uses incorporate vowels, they seem to me to belong in a discussion of the vowels. In either case, it is important to recognize รร as a special case if you come across it in a Thai word.


You did it! This whirlwind tour has examined the major features of Thai syllables, starting from a point of no Thai reading experience. Beginning from Part I, you were introduced to syllable anatomy diagrams. Working with them is a powerful technique that encourages spatial visualization of the phonemic construction of a syllable. You learned how to break simple syllables apart into their constituents.

In Part II, you learned that initial consonant clusters must be treated much the same as simple initial consonants. In particular, you saw that it’s important not to break consonant clusters out into separate syllables, unless they get ‘heavy’ enough to break out naturally. Normally, they must remain clustered so that we can determine the proper tone and more easily read syllables with preposed vowels. Surprisingly, this way of thinking of clusters, while much closer to the conception of native Thais, is not taught in most beginning and intermediate Thai-learning texts for foreigners.


  1. Further information on consonant clusters is available in the reference page, Consonant Clusters.
  2. This rule applies when the second consonant of the cluster is low-class, as it almost always is. The rule will be refined later in this article.
  3. False cluster รร is not addressed in this section.
  4. Richard Wordingham informs us that the technical term for this tone-carry-forward behavior is ‘rightward register spreading.’ He further notes that "in Khmer, it’s called ‘vowel governance’...if the first syllable starts with an oral stop or fricative and the second doesn’t, the the consonant of the first syllable determines the ‘register’ of the second."
  5. This (now discouraged) process of conceptually ‘moving’ the preposed vowel used to be called Preposed Vowel Inversion or the Special Spelling Rule on this website. Following the guidance in this article, it is no longer necessary.

These articles by Glenn Slayden
Thanks to David Rubin, Rikker Dockum, and Richard Wordingham
originally posted: January 22, 2008
updated: March 23, 2008, January 10, 2010
Copyright © 2023 Portions copyright © by original authors, rights reserved, used by permission; Portions 17 USC §107.