How Thai Vowels Work

Question

I am trying to put together a worksheet to understand how the Thai script works. I am looking here and here. The wiki page seems to suggest that there are two types of symbols: combining characters and standalone characters, whereas omniglot says every vowel is a combining character.

I'm wondering if one could explain briefly how to apply the vowel symbols, and what all the vowel symbols are in practice. My question is basically, if they are all combining characters, and if every vowel symbol can combine with every consonant. Also, it sounds like it might be more complex than that, where a combining character combines with a whole group of consonants, not sure.

Essentially though, I would like to know this:

1. What all the vowel characters are (and if they are both standalone and combining).
2. For the combining ones, if they can be combined with every consonant, or generally what the rules are for combining them.

Answer 1

I believe that this question comes from misunderstanding between the orthography and typography.

From the typography point of view, you don't care how characters "encode" sounds. Your only concern is symbols and glyphs and how they combine on print. These characters can be:

• standalone characters — that take horizontal space, like the Latin A, and
• zero-width combination characters, like Extended Latin ̈ ("COMBINING DIAERESIS" U+0308) which combines with the preceding character, forming a combined character Ä.

From orthography point, in complex scripts like Thai, you always look at the entire syllable, so one may argue that every vowel character is a combination character that "stick" around the consonant, just like the Umlaut "sticks" to the "A".

Note that Thai vowels can stay on the left, right, top, or bottom of the consonant.
Consider these examples¹:

1. ก + ◌า = กา /k/ + /aa/ = /kaa/ (²)
2. ก + เ◌ = เก /k/ + /ee/ = /kee/
3. ก + แ◌ = แก /k/ + /aee/ = /kaee/
4. ก + ◌ิ = กิ /k/ + /i/ = /ki/
5. ก + เ◌า = เกา /k/ + /au/ = /kau/

…a combining character combines with a whole group of consonants…

Correct. Many vowels (including diphthongs and triphthongs) are combinations of several "simpler" ones.

Note example #5. From the typography view, there are two combination characters: ee and aa (you may have noticed them in previous examples ##1 and 2). However, from the orthography point, being used together, these two characters denote a single vowel (diphthong) au and never ee or aa.

Yet another example:

6. ก + เ◌ีย = เกีย /k/ + /ia/ = /kiia/

Here again, typographically three combination characters (which alone stand for /e/, /ii/, and /y/, correspondingly) denote a diphthong /iia/.

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¹) the dotted circle represents a placeholder which is substituted with a single consonant character.
²) double vowel in a transliteration stands for a long vowel.