Codas and the six-way merge¶
Thai phonotactics allows only six coda consonant phonemes. However, the orthography has 26 letters that can appear in coda position (plus semi-vowels ว and ย). Every coda position letter maps to one of the six phonemes — and in some cases to a semi-vowel offglide. This mapping is called the six-way final-consonant merge or, using a traditional Thai grammar term, the "collapse" of final consonants.
The six coda phonemes¶
| Phoneme | IPA | Manner | Example |
|---|---|---|---|
| /m/ | m |
bilabial nasal | กาม |
| /n/ | n |
alveolar nasal | กาน |
| /ŋ/ | ŋ |
velar nasal | กาง |
| /p̚/ | p̚ |
bilabial unreleased stop | กาบ |
| /t̚/ | t̚ |
alveolar unreleased stop | กาด |
| /k̚/ | k̚ |
velar unreleased stop | กาก |
Plus two semi-vowel offglides that make syllables live: - /w/ from ว - /j/ from ย
The collapse table¶
| IPA coda | Thai orthographic letters |
|---|---|
m |
ม |
n |
น ณ ญ ร ล ฬ |
ŋ |
ง |
p̚ |
บ ป พ ภ ฟ |
t̚ |
จ ช ซ ฌ ฎ ฏ ฐ ฑ ฒ ด ต ถ ท ธ ศ ษ ส |
k̚ |
ก ข ค ฆ |
w |
ว (semi-vowel offglide) |
j |
ย (semi-vowel offglide) |
The large number of letters for /t̚/ (17 letters) reflects the many different historical origins of Thai vocabulary — Sanskrit loans, Pali loans, native Thai words — all using different letters for the same final sound.
Phonological motivation¶
The merge is not an arbitrary convention — it reflects the actual phonological behaviour of Thai:
- Thai forbids consonant aspiration and voicing contrasts in coda position. A voiced obstruent, when used as a final, is pronounced as the corresponding voiceless unreleased stop.
- The three stop positions (bilabial, alveolar, velar) are all that the phonology supports in coda position.
- The six-way merge produces a coda phoneme that can be unambiguously pronounced by any speaker, even in rapid speech.
Foreign coda exceptions¶
Modern loanwords introduce phonemes in coda position that native Thai phonotactics does not permit. The most common cases:
| Foreign coda | Thai orthography | Native collapse | Preserved under |
|---|---|---|---|
| /f/ | ฟ | /p̚/ | everyday profile for lexicon-listed loans |
| /s/ | ส ศ ษ | /t̚/ | careful_educated profile for some loans |
| /l/ | ล | /n/ | careful_educated profile for some loans |
The engine handles these via a loanword lexicon. Each listed word has a profile-specific annotation indicating whether the foreign coda should be preserved or collapsed. Under etalon_compat, all foreign codas collapse.
See Reading profiles for how the active profile controls preservation. Scheme-specific details: TLC, RTL, Paiboon / Paiboon+.
Impact on syllable type¶
The coda phoneme determines whether a syllable is live or dead:
- Live syllable — ends in a nasal or semi-vowel coda (/m n ŋ w j/), or has a long vowel in open position.
- Dead syllable — ends in an unreleased stop (/p̚ t̚ k̚/), or has a short vowel in open position.
This distinction feeds directly into the tone matrix. The same onset class and tone mark produce different tones in live vs. dead syllables.
See Tone derivation for the full table.