Practice: blend it or split it
What you will be able to do
Look at two consonants at the start of a Thai word and know whether they blend into one sound, split into two syllables, or hand a class forward — and get the tone that follows right.
Two consonants at the start of a word do one of three things. A true cluster blends into a single sound and takes its tone from the FIRST letter. ทร is the false cluster and is read s. Anything else is a leading pair: put a short a after the first letter, and let that letter hand its class to the second syllable only when the second consonant is one of ง ญ ณ น ม ย ร ล ว ฬ. Before any other letter, the second syllable is toned from its own class.
How is this word read?
ปลา
ปล is one of the fifteen true clusters, so the two letters blend and the word is one syllable. ป is middle class and the syllable is live, which gives a mid tone: bplaa, fish. bpà-laa splits a cluster that does not split. bplàa blends correctly but puts a low tone on a live middle-class syllable, and only a tone mark could put it there. bpà-lǎa makes both mistakes at once.
Which letter's class decides the tone of this word?
ครับ
The tone of a true cluster comes from the class of the FIRST letter, always. ค is low class, and the syllable is dead with a short vowel, which gives high: khráp. ร is the second half of the blend and carries no class of its own. บ is the final consonant; it makes the syllable dead, which the tone rule then uses, but it brings no class with it.
How is this word read?
ทราย
ทร is the false cluster, and it is read s. ท is low class and the syllable is live, so the tone is mid: saai, sand. thraai blends the two letters as they are written, which is the one pair where you must not. thá-raai treats them as a leading pair, which they are not — and note that ท is low class, so even that mis-reading would take a high tone on its inserted syllable, never a low one. sǎai has the right consonant but a rising tone, and a low-class initial in a live syllable cannot rise.
Which tone does the second syllable of this word carry?
ขนม
น is one of the ten low-class letters with no high-class partner, so ข hands its high class forward. The syllable นม is live, and a high-class initial in a live syllable rises: khà-nǒm, sweets. Mid is what you get by toning นม from น's own low class, which is exactly the mistake this step exists to stop. Low is the tone of the first syllable, not the second. Falling would need a tone mark, and there is none written.
How is this word read?
ตลาด
ล is in the list of ten, so ต hands its middle class forward. ลาด is dead with a long vowel, and a middle-class initial there gives low: dtà-làat, market. dtà-lâat is what you get by leaving ล on its own low class, where a dead long syllable falls. dtà-lǎat would need a high-class initial. dtlàat blends ตล, but ตล is not one of the fifteen true clusters.
How is this word read?
สบาย
บ is middle class, and no middle-class letter is in the list of ten, so nothing is handed forward. บาย is live, and a middle-class initial in a live syllable is mid: sà-baai, comfortable. sà-bǎai applies the handing-forward rule where it does not belong. sà-bâai would need a tone mark. sǎ-baai gets the first syllable wrong: ส is high class in a dead short syllable, which gives low.
Which tone does the second syllable of this word carry?
สภาพ
ภ is a low-class letter that does have a high-class partner, so it is not in the list of ten and keeps its own class. ภาพ is dead with a long vowel, and a low-class initial there falls: sà-phâap, condition. Rising would need a high-class initial. Mid is impossible, because an unmarked dead syllable never comes out mid. Low is what you get by wrongly handing ส's high class forward.
How is this word read?
สวัสดี
ว is one of the ten, so ส hands its high class to the middle syllable. วัส is dead with a short vowel, and a high-class initial there gives low: sà-wàt-dii. sà-wát-dii is the reading you get without the handing forward, because ว on its own low class in a dead short syllable goes high. sǎ-wàt-dii rises on ส's own syllable, which is dead and short and therefore low. sà-wàt-dìi lowers ดี, but ด is middle class and that syllable is live, so it is mid.
How is this word read?
กลาง
กล is one of the fifteen, so it blends and the word is one syllable. ก is middle class and ง keeps the syllable live, which gives mid: glaang, middle. gà-laang splits a true cluster into a leading pair. glâang and glǎang both put a tone on a live middle-class syllable that only a tone mark could put there, and no mark is written.
How is this word read?
คน
Ask first whether the second consonant simply closes the syllable, and here it does: nothing follows น, so it is a final and the word takes the implicit o. ค is low class and the syllable is live, which gives mid: khon, person. khà-nǒn and khà-non both split one syllable into two, borrowing the leading-pair pattern of a word like ถนน, thà-nǒn, where a leader really does take a short a — คน has no leader, because น is already spoken for as the final. khǒn keeps one syllable but rises, and a low-class initial in a live syllable cannot rise.
How is this word read?
นก
ก closes the syllable, so this is one syllable with the implicit o, not a pair. น is low class and the syllable is dead with a short vowel, which gives high: nók, bird. nòk is impossible, because an unmarked low-class dead syllable never comes out low. nôk would need a long vowel, since that is when a low-class dead syllable falls. nà-gò treats a final as the start of a second syllable.
Which pair below is one of them?
Fifteen pairs of consonants at the start of a word genuinely blend into a single sound.
ผล is on the list of fifteen. ผร is not, because ผ blends with ล only and never with ร. ขน is a leading pair, as in ขนม, where a short a goes between the two letters and the class is handed forward. ทร is the false cluster: the letters sit together, but they are read s.
What is happening between the first two letters of this word?
ตรง
ตร is one of the fifteen true clusters, so the two letters are pronounced together and the word is one syllable: dtrong, straight. No short a is inserted, because that happens only in a leading pair. Only ทร is read that way, and there it is the pair that says s, not ท on its own. And a silent leader that sets a class is ห or อ, neither of which is written here.
Which tone does that syllable take?
The second syllable of a two-syllable word begins with บ and ends in a long vowel with nothing after it.
บ is middle class, and the list of ten letters that take a class handed forward contains no middle-class letter, so บ keeps its own. A long vowel with nothing after it makes the syllable live, and a middle-class initial in a live syllable is mid — which is why สบาย is sà-baai. Low is the middle-class dead result, and this syllable is not dead. Rising is what you get by wrongly handing a high class forward, the mistake that produces sà-bǎai. Falling would need a tone mark.
Common mistake
Handing the class forward where it does not belong. สบาย is sà-baai and not sà-bǎai, because บ is middle class and keeps what it has; สภาพ is sà-phâap for the same reason. The mirror mistake is failing to hand it forward, which turns สวัสดี into sà-wát-dii and ตลาด into dtà-lâat.