Thai has three types of consonants: “middle” consonants, which are simply regular consonants; “high” consonants, which follow certain rules; and “low” consonants, which follow certain other rules. Within the low consonant class, there are “single” low consonants and “paired” low consonants. Paired low consonants match the high consonants, so we start with these. For simplicity’s sake, I am including in the below table only the primary consonant, rather than (for example) all the different ways one can make the “s” sound. “kh,” “th” and “ph” are aspirated k, t and p, respectively.
To make it more confusing, high consonants can only have low, falling, and rising tones, while low consonants can only have no, falling, or high tones, and the tone markers for the low consonants are effectively “one off” from the tone markers used for high and middle consonants – i.e., a falling-tone high or middle consonant and a high-tone low consonant get the same tone marker. In some respects, this makes things easy: if you hear a word beginning with “kh” that has a high tone, you know that you have to spell it with the ค and not the ข – but it would be easier still just to have one set of letters and one set of rules.
|no tone||low tone||falling tone||high tone||rising tone|
My teacher tells me that grammar school students learn this over the course of four years.