Thai Language Blog

The Invisible Vowel Rules, part 1 Posted by on Sep 20, 2012 in Beginner, Intermediate

When I teach Thai to my students, they always freak out when I tell them about vowel locations. In English, words are pronounced left to right. You pronounce the first letter of the word first, and the last letter last. But not so in Thai! Vowels are written above, below, to the left, to the right, and even surrounding the consonants. For a beginner it’s an unintuitive concept.

Then I tell my students that sometimes the vowel isn’t even written, that it’s invisible. When they see a long series of consonants together with no vowels to be found, they start to question the sanity of whoever invented the Thai language . . .

So how do you know how to pronounce a Thai word without visibly defined vowels?

Enter: The invisible Vowel rules (Thai translation is สระลดรูป sa2ra2 lod2 ruub3). These aren’t official rules, however. I wrote these as they are as an easy way for beginners to remember and learn them.

There are four rules to this.

1) If there are two consonents, the vowel is a short ‘o’ sound such as in โอะ.

2) If there are three consonents with no vowels, the first vowel is a short ‘a’ and the second is a short ‘o’such as อะโอะ.

3) If the second consonant is ว, then replace ว with the ‘uwa’ sound, อัว.

4) If the first syllable is an *alone* consonant of ก/ท/ธ/ม/ห, and the following syllable starts with ร, the implied vowel is อ.



Examples of the first rule:

ลด – lod

มด – mod

รถ – rot

สะกด – sagod



Examples of the second rule:

ผสม – pasom

ระบบ – rabob

In this example, the first vowel is known, but the second is not. Follow the rule for only the unknown vowel.


สนุก – sanuk

สระ – sara

In the last two examples, the second vowel is already known but the first is not. Follow the rule for only the unknown vowel.



Examples of the third rule:

บวก – buak

This comes from บัว + ก


สวน – suan

This comes from สัว + น


Examples of the fourth rule:

มรดก – mawradok


This example also uses the 2nd rule. Words that use the fourth rule are very rarely found, so no need to sweat over it.



Sometimes, words use multiple rules:

ขบวน kabuan

2nd rule + 3rd rule


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  1. Bernard Le Du:

    I think there is a problem with what you wrote as rule N°1 :
    in this cas is not a short “a” but a short “o” as your examples demonstrate correctly just under :

    ลด – lod
    มด – mod
    รถ – rot
    สะกด – sagod

    Best regards. Bernard

    • palmisano:

      @Bernard Le Du Thanks for catching my mistake. I was having one of those ‘moments’ lol . . .

  2. sad:

    Thank you so much! I’ve been looking for an easy explanation for this for years!

  3. Marcin:

    Thanks for this!

  4. Pepper:

    With so may ‘t’ ‘k’ and ‘s’ sounding consonants how do we choose which one to use in our sentences when we speak or write or doesn’t it matter if they all make the same sound? Silly question but it’s made me quite confused

  5. Allen:

    Is my Thai transcription correct when I apply it to one of your example that you have. for instance : มด where as both consonant have a initial and final positioning. example: ม initial position is (m-) and ด final position is (-t) so wouldn’t that be mot instead of mod. and can you explain the reason why not…
    Also can you direct me to material that would clarify the concepts behind your example. if I am not correct.

    Thank you