Negating past one-time actions in Thai with ไม่ได้ (mâi dâai)

To negate a one-time action that wasn’t done, don’t use ไม่ (mâi) + verb. Instead, use ไม่ได้ (mâi dâai) + verb. For example: I didn’t go to school yesterday = ฉันไม่ได้ไปโรงเรียนเมื่อวาน (chăn mâi dâai bpai rohng riian mêuua waan) "Not going to school yesterday" is a “one-time” action. But if you want to say that, in general, you don’t go to school - whether in the past or in the present you would use ไม่ (mâi) + verb. For example: I don’t go to school/I didn’t used to go to school. = ฉันไม่ไปโรงเรียน (chăn mâi bpai rohng riian) “Not going to school” in general is not a “one-time” action. It’s an on-going habit - whether in the past or present depending on the context. Important: don’t get confused with …ไม่ได้ (…mâi dâai) which means “cannot”. The one we are dealing with must be followed by a verb. Note: To understand, to hear, to know, to see, etc, are not “active” actions. They are verbs but they are “passive/abstract” verbs. With these “passive/abstract” verbs, just use ไม่ (mâi) to negate them every time.