Yes/No Questions with ไหม

One word turns a statement into a question

Thai does not reorder anything to ask a question. There is no do-support, no inversion, no auxiliary appearing from nowhere. You say the statement and put mai (ไหม) on the end. You like Thai food becomes you like Thai food mai. Is it delicious becomes delicious mai. The rest of the sentence is untouched, which makes this one of the easiest wins in the language. In everyday speech mai is often pronounced closer to mái with a high tone, and you will see it written มั้ย in casual text. Both are the same word.

Answering without a word for yes

Thai has no all-purpose yes. You answer a mai question by repeating its verb. Asked 'delicious mai', you answer 'delicious'. Asked 'do you like it', you answer 'like'. For no, put mai (ไม่) in front of that same verb. Note that this negating mai and the question-marking mai are different words with different tones and different spellings, which is confusing for exactly one week and then never again. Add your politeness particle to either answer. A bare repeated verb with no particle is fine between friends and abrupt with anyone else.

Asking whether someone wants something

ao (เอา) means take or want, and ao mai is the workhorse question of Thai shopping and hospitality: do you want it? Someone will ask you this about bags, chilli, ice, receipts and sauce a dozen times a day. The answer is ao (yes, I will take it) or mai ao (no thanks). Adding khrap or kha makes it courteous rather than curt. The same pattern works for any verb of wanting or trying: yak pai mai (do you want to go), long chim mai (want to try tasting it).

Have you done it yet?

For a question about something completed, Thai uses a different ending: rue yang (หรือยัง), meaning 'or not yet'. kin khao rue yang is 'have you eaten yet', and it is a genuine greeting, not an offer of food. Answer with laeo (แล้ว, already) or yang (ยัง, not yet). kin laeo means I have eaten. yang means not yet, and yang mai kin makes it explicit. Keep the two endings apart in your head: mai asks do you, rue yang asks have you yet.

Questions you will actually be asked

Half of learning to answer is recognising the question fast enough. These are the ones a visitor hears most often, so learn to spot the mai on the end before you have finished parsing the rest.

Answering with a word for yes

chai (ใช่) does mean yes, but it answers a different kind of question - one about identity or fact, of the 'is that right?' sort. Using chai to answer 'is it delicious mai' sounds off, in the way answering 'do you like it?' with 'correct' would in English. Stick to repeating the verb. It feels strange at first and then becomes automatic, and it is one of the fastest ways to stop sounding translated.

Mixing up the two mai words

The question mai (ไหม) goes at the end. The negative mai (ไม่) goes in front of the verb. Put the negative one at the end and you have said nothing; put the question one in front of the verb and you have said nothing. A sentence can contain both, and that is the sentence to practise until it is comfortable: mai pai mai (ไม่ไปไหม), 'are you not going?'.