Mid Tone is the Hard Tone
It’s safe to say that new learners pick up the first three tones pretty easily (in the traditional order — ฟา ฝ่า ฝ้า ฟ้า ฝา — is there a word for this order?) The final tone (เสียงจัตวา) is not bad either. Most new learners need to practice เสียงตรี until they get it, but it’s achievable.
Today I expose the dirty little secret about Thai: the mid tone (or “common tone,” เสียงสามัญ) is the hardest by far. Actually the true difficulty is the ambiguity between the mid tone and the low tone. Without context, side-by-side contrast, repetition, or very focused concentration, it’s hard to hear the difference.
My “natural” tone is definitely the low tone (เสียงเอก). When challenged to utter a single, clear, mid-tone syllable (for example, แก), I often fail and just say “old.” ให้แก: no problem. คำว่า แก เฉยๆ ไม่ได้เดดขาด. It’s hilarious. Notably, native Thai speakers do not have this problem whatsoever.
Fortunately, in real conversation, there is always context, so in practice it’s a non-issue. Tellingly, no Thai has ever noticed me mispronounce the mid tone. For a while, I pronounced “year” and “hit” with the low tone, but in mid-sentence, it is either not noticeable or at any rate not worth mentioning.