Practice: which no?
What you will be able to do
Refuse, deny and correct with the right negative — choosing deliberately between ไม่, ไม่ได้, ไม่เป็น, ไม่ไหว, ไม่ออก, ยังไม่, เปล่า and ไม่ใช่ — and hear why ไม่ได้ไป and ไปไม่ได้ are opposite sentences.
Thai has no all-purpose no. Which negative you reach for is settled by what you are denying — an action that did not happen, a skill you never learned, a limit you have reached, a label that is simply wrong — and by where you put ได้. In front of the verb, ไม่ได้ denies that something happened. Behind the verb, the same word denies that it is possible.
Which sentence denies it?
the wrong dish has landed on your table and you want to say you did not order it
ไม่ได้ (mâi dâi) in front of the verb denies that the action took place, which is exactly the claim you need about an order already given. ผมไม่สั่งอันนี้ is a habit or a decision about now, "I don't order this" or "I'm not ordering this", so it comes out as a change of mind rather than a mistake in the kitchen. Move ได้ behind the verb and ผมสั่งอันนี้ไม่ได้ says the ordering cannot be brought off — that you are unable or not allowed to order it. ไม่ใช่ needs a noun after it, or ว่า and a whole clause; put it straight in front of a bare verb and there is nothing for it to reject.
What does it say?
ไปไม่ได้ครับ
ได้ sits behind the verb here, so it takes hold of the outcome of that verb: the going cannot be brought off. Nothing else in the sentence would have to change to make it "I didn't go" — that is ไม่ได้ไป, the same three words with ได้ in front, where it takes hold of the whole event instead. "I'm not going" is plain ไม่ไป, a decision about now or later with no question of ability in it. "I haven't gone yet" needs ยัง in the sentence, as ยังไม่ได้ไป, and faces forward at something still to come.
Which can't is it?
you never learned to swim, and a friend is waving you into the pool
ไม่เป็น (mâi bpen) after the verb is the never-learned-it can't, and never having learned is precisely the situation. ว่ายน้ำไม่ได้ says something is stopping you today — a wound, a current, a rule — and leaves your friend thinking you swim perfectly well the rest of the time. ไม่ไหว is the limit-reached can't, so it claims you can swim but have nothing left in the tank. ไม่ออก belongs to things that will not come out or resolve, as in อ่านไม่ออก and คิดไม่ออก, and it does not attach to a physical skill at all.
Which sentence says so?
your host has the ladle over your plate again and you could not manage another mouthful
ไม่ไหว (mâi wǎi) after the verb is the capacity-spent can't, and อิ่มแล้วครับ กินไม่ไหว is the whole move: full, cannot manage more, without turning the food itself down. ไม่ได้กิน puts ได้ in front of the verb and so denies that you ate at all, which is untrue and does nothing to stop the ladle. กินไม่เป็น would claim you never learned how to eat. กินไม่ออก is not a phrase Thai uses at all: it is ไม่ออก that belongs with อ่านไม่ออก, ฟังไม่ออก and คิดไม่ออก, where a meaning will not come out, and a full stomach is nothing to decode.
Which can't fits?
a Thai friend has scrawled the address by hand; you read Thai, but these letters defeat you
ไม่ออก (mâi àwk) is the failure-to-decode can't: the meaning will not come out, exactly as in ฟังไม่ออก when speech goes past you and คิดไม่ออก when a word will not surface. อ่านไม่เป็น would say you never learned to read Thai, and you did. อ่านไม่ไหว says you have run out of capacity for reading, which is a statement about you rather than about the handwriting. ไม่ได้อ่าน has ได้ in front of the verb, so it denies that you read it at all — a different claim, and one that sounds like an excuse.
You have not eaten. Which answer works?
กินข้าวหรือยังครับ
A question ending in หรือยัง has a closed pair of answers, แล้ว or ยัง, and ยัง on its own is complete and entirely natural. ไม่ยัง is the beginner giveaway the lesson warns about: the form does not exist in Thai. A bare ไม่ is not an answer either, because Thai answers with the verb from the question — the long way round here is ยังไม่ได้กินครับ. เปล่า (bplàao) removes an assumption a question carried, or answers a tag ending in หรือเปล่า, and this question assumed nothing.
What has the speaker told you?
ยังไม่ได้กินครับ
ยัง makes it "so far", and ได้ in front of the verb makes it about what has happened rather than about what he intends, so the sentence faces forward at a meal still to come. Finished would be กินแล้ว. Stopped is the mirror construction ไม่ … แล้ว, as in ไม่กินแล้ว, which faces back at a decision already taken. A plain habit, he does not eat, is ไม่กิน with no time in it at all. Drop the ได้ and you get ยังไม่กิน, which comes out closer to "I'm not eating yet" — intention rather than record.
Which reply tells him the habit is over?
you smoked for years and gave up; a friend holds out the packet
แล้ว (láew) marks a change of state, so ไม่ … แล้ว is "not any more" and points back at the decision you already took. ยังไม่สูบ says the opposite thing about time, that you have not started yet, which invites him to keep the packet out. ไม่เคยสูบ denies that the habit ever existed, and yours did. สูบไม่ได้ puts a circumstance or a rule in the way — a ward, a petrol pump — rather than a choice, and he will look round for the sign.
Which negative does the sentence need?
you have lifted a bag off the carousel and it turns out not to be yours
ของผม is a noun phrase, and ไม่ has nothing predicate-shaped to attach to, so ใช่ has to supply it: ไม่ใช่ (mâi châi) means "that is not the one". อันนี้ไม่ของผม is not a broken sentence but no sentence at all, the way "I not doctor" has no verb in it. ไม่ได้ in front denies an action and there is no action here; the form that does work in front of a noun keeps เป็น, as ไม่ได้เป็น, and its job is denying a claim someone has just made about you. ไม่เป็น after a verb already has its own job, the never-learned-it can't of ว่ายน้ำไม่เป็น, and it cannot carry a noun.
Which one lets her off without ordering her about?
a colleague is settling in to wait for you at the gate, and you do not want to put her to the trouble
ไม่ต้อง (mâi dtâwng) is "no need", and that is a kindness: it removes the obligation without issuing an instruction. อย่า (yàa) is the negative imperative aimed at a person, so อย่ารอครับ tells her not to wait, and mixing those two is how learners accidentally order someone about when they meant to let them off. ห้าม (hâam) is the regulation word from signs, ห้ามจอด, ห้ามสูบบุหรี่, and the agent behind it is the rule rather than you; pointed at a colleague it sounds as though waiting were prohibited. ไม่รอ is only a statement that someone is not waiting, and with the subject dropped, as Thai drops it, she will take it as being about you.
You have been in all evening. What do you say back?
ไปไหนมาครับ
เปล่า is an answer word, not a negative particle. Its ordinary meaning is empty, as in มือเปล่า, and as a reply it stands alone and takes away the assumption the question carried — that you went somewhere — after which the detail follows: เปล่าครับ ไม่ได้ไปไหน. ผมเปล่าไป does not exist, because เปล่า cannot negate a verb inside a sentence; it is an answer word and a question tag, nothing more. A bare ไม่ is not an answer, since Thai hands back the verb from the question. ยัง belongs to a question ending in หรือยัง, and this one asked where, not whether yet.
Which refusal will not sound abrupt?
a neighbour you barely know offers to drive you to the clinic
ไม่เป็นไร (mâi bpen rai), literally "it isn't anything", is the standard soft no to an offer of help, a bag, a lift or another spoonful, and ไม่เป็นไรครับ ขอบคุณครับ is the two-piece refusal that carries you through most doorways. ไม่เอา refuses an object being handed to you across a counter, which is normal there and not rude; here there is no object, so it lands as a flat "don't want" aimed at the offer itself. เปล่า only removes an assumption behind a question, and he asked you nothing. ไม่ใช่ rejects a statement as untrue, and he has not made one.
Which one keeps it small?
you feel slightly off, not ill enough to worry anyone, and a colleague asks how you are
ไม่ค่อย (mâi khâwy) weakens the negative to "not very, not really", and it is worth having, because a flat ไม่สบาย already sounds more serious than most learners intend. เลย (loei) after the negated word pushes the other way, to "not at all well", which is what you say when you mean it. ไม่ได้ in front denies a claim somebody has made about you, on the pattern of ผมไม่ได้โกรธ, and nobody has claimed you were well. ไม่ … แล้ว marks a change of state, so it announces that you have become unwell — bigger news than you meant to give.
The card machine is down. What comes back?
จ่ายด้วยบัตรได้ไหมครับ
Listen to the last two syllables of the question and your no has already been chosen for you: a question closed with ได้ไหม comes back as ได้ or ไม่ได้, and ไม่ได้ค่ะ is a complete answer meaning it is not possible — not the opening of a negotiation. ไม่จ่าย hands back the main verb, which is the right move for a ไหม question built on that verb but not for this shape, and it says she is not paying. ไม่ใช่ belongs to a … ใช่ไหม question, where a statement has been put in front of you to judge. ยัง answers หรือยัง, so it would say the payment has not happened yet rather than that it cannot.
Common mistake
The commonest real mistake is putting ไม่ได้ in front of the verb when you mean "I can't". ไม่ได้กินเผ็ด reads as a report about the past, "I didn't eat spicy food", and it is not a reliable way to keep the chillies out. Two forms do work and they do not say the same thing: ไม่กินเผ็ดครับ is the habit, and กินเผ็ดไม่ได้ครับ is the inability, which is the one to use when there is a medical reason. Decide first whether you are describing a habit, an inability or the past, then place the negative — before the verb it looks backwards in time, after the verb it looks at what is possible.
Next: Saying no: the negatives