Korean has two negation adverbs, and English gives you no reliable instinct for choosing between them, because English "can't" and "don't" overlap in ways Korean refuses to. 안 negates volition or plain fact — "doesn't / won't (by choice) / isn't." 못 negates ability or possibility — "can't," because capacity, circumstances, or permission block the action. Same slot in the sentence, opposite meanings. This page is the tiebreaker: how to know, every time, which one you need.
The core distinction in one line
안 = you don't / won't — it's your choice, or simply a fact. 못 = you can't — something is stopping you.
Everything else follows from that. If the action fails to happen because you'd rather it didn't, or because it's just not the case, use 안. If it fails because you're unable — no time, no skill, sick, forbidden — use 못.
저는 술을 안 마셔요.
jeoneun sureul an masyeoyo
I don't drink. (I choose not to)
저는 술을 못 마셔요.
jeoneun sureul mot masyeoyo
I can't drink. (my body can't handle it)
Both are perfectly grammatical. They just tell different stories about why the drinking isn't happening — and to a Korean ear, the difference is not subtle.
The one-question test
When you're unsure, ask: is a reason blocking the action? If you can point to an obstacle — "no time," "I'm sick," "I'm not allowed," "I don't know how" — you want 못. If the only thing behind it is your own preference, or it's simply a stated fact, you want 안.
| Situation | Which | Sentence |
|---|---|---|
| You just don't feel like going | 안 | 그냥 안 갔어요 |
| You had no time, so you couldn't go | 못 | 시간이 없어서 못 갔어요 |
| You don't drink, on principle | 안 | 술을 안 마셔요 |
| You physically can't drink | 못 | 술을 못 마셔요 |
시간이 없어서 못 갔어요.
sigani eopseoseo mot gasseoyo
I couldn't go because I had no time.
그냥 안 갔어요.
geunyang an gasseoyo
I just didn't go. (didn't feel like it)
Notice how the presence of a reason clause (시간이 없어서, "because there was no time") pulls you toward 못. When an obstacle is named, 못 is almost always the right choice.
The social stakes: choosing wrong can sting
Here's why this isn't just a grammar nicety. English "I can't come to the party" politely hides why — maybe you're busy, maybe you'd just rather not, and the listener can't tell. Korean strips that cover away. Say 파티에 안 가요 and you've announced you choose not to come — which, to the host, can sound blunt or even rude. Say 파티에 못 가요 and you've signaled you wish you could but something prevents you — the polite, face-saving option.
내일 모임에 못 갈 것 같아요.
naeil moime mot gal geot gatayo
I don't think I'll be able to make it to the gathering tomorrow. (softer — implies I wish I could)
저는 운전 못 해요.
jeoneun unjeon mot haeyo
I can't drive. (I never learned / don't have a license)
This is why, when you're declining an invitation, 못 is usually the kinder, more natural choice even if the real reason is partly preference: it frames the "no" as regret rather than refusal. Reaching reflexively for 안 when declining is a classic way to sound colder than you mean to.
The hard rule: adjectives take only 안
There is one absolute boundary. 못 attaches only to action verbs. Adjectives (descriptive verbs like 크다, 예쁘다, 비싸다, 좋다) describe states, and a state isn't something you're "able" or "unable" to do — so 못 is simply ungrammatical on them. Adjectives negate only with 안 (or the long -지 않다).
❌ 이 가방은 못 비싸요.
Incorrect — 비싸다 is an adjective; you can't be 'unable to be expensive'.
✅ 이 가방은 안 비싸요.
i gabang-eun an bissayo
This bag isn't expensive.
The takeaway: 못 lives in the world of doing; adjectives live in the world of being. No adjective ever takes 못.
The long forms mirror the same split
The 안 / 못 contrast carries straight up into the formal register. The long forms simply move the negation onto an auxiliary, but the meaning split is identical: -지 않다 is the formal "won't / doesn't," and -지 못하다 is the formal "can't."
| Choice / fact | Ability | |
|---|---|---|
| Casual (spoken) | 안 가요 | 못 가요 |
| Formal (written) | 가지 않아요 | 가지 못해요 |
So the choice you make between 안 and 못 is the same choice whether you're speaking casually or writing formally — only the surface form changes.
Common Mistakes
1. Defaulting to 못 for every negative. 못 specifically means "unable." If it's a choice or a plain fact, you need 안.
❌ 저는 담배를 못 피워요.
Misleading if you simply choose not to smoke — that's 안 피워요.
✅ 저는 담배를 안 피워요.
jeoneun dambaereul an piwoyo
I don't smoke. (by choice)
2. Using 안 to decline an invitation. It can sound like a flat refusal; 못 frames it as regret.
❌ 미안해요, 내일 결혼식에 안 가요.
Off-key — 안 가요 says you choose not to attend the wedding; use 못 가요.
✅ 미안해요, 내일 결혼식에 못 가요.
mianhaeyo, naeil gyeolhonsige mot gayo
Sorry, I can't make it to the wedding tomorrow.
3. Putting 못 on an adjective. Adjectives negate only with 안.
❌ 방이 못 깨끗해요.
Incorrect — 깨끗하다 is an adjective; use 안 깨끗해요.
✅ 방이 안 깨끗해요.
bang-i an kkaekkeutaeyo
The room isn't clean.
4. Using 안 when a real obstacle is blocking you. If a reason stops you, it's 못.
❌ 배가 아파서 안 먹어요.
Misleading — if a stomachache prevents you, it's 못 먹어요.
✅ 배가 아파서 못 먹어요.
baega apaseo mot meogeoyo
My stomach hurts, so I can't eat.
Key Takeaways
- 안 = choice or plain fact ("won't / doesn't / isn't"); 못 = blocked ability ("can't").
- Test: a reason blocking you (no time, sick, not allowed, don't know how) → 못; your own preference → 안.
- Declining invitations: default to 못 (못 가요) — it's the polite, face-saving frame; 안 can sound like a cold refusal.
- Adjectives take only 안, never 못 (✗못 비싸요 → 안 비싸요).
- The same split runs through the formal long forms: -지 않다 (choice) vs -지 못하다 (ability).
Now practice Korean
Reading grammar gets you part of the way. The exercises are where it sticks — free, no signup needed.
Start learning Korean→Related Topics
- Short Negation: 안TOPIK 1 — The everyday 'not' — how the adverb 안 negates verbs and adjectives, why noun+하다 action verbs split into 공부 안 해요, and how 안 (won't/don't by choice) differs from 못 (can't).
- 못: Can't / InabilityTOPIK 1 — The adverb 못 negates ability, not choice — 못 가요 'can't go', 못 먹어요 'can't eat'. It sits before the verb, splits noun+하다 verbs the way 안 does (공부 못 해요), attaches only to action verbs, and hides two tricky pronunciations: 못 해요 [모태요], 못 가요 [몯까요].
- Suppletive Negatives: 있다 → 없다, 알다 → 모르다, 이다 → 아니다TOPIK 1 — A small set of high-frequency predicates negate by swapping in a whole different word, not by adding 안 or 못 — existence 있다 → 없다, knowledge 알다 → 모르다, and the copula 이다 → 아니다 (with the noun taking 이/가). Ordinary adjectives still negate normally with 안.
- 안 vs 못: Won't or Can'tTOPIK 1 — Both negate the verb, but 안 negates by choice or plain fact ('do not / is not') while 못 negates by inability ('cannot' — blocked by capacity, circumstance, or permission); the deciding line is volition versus impossibility.
- 못 vs 안: Can't vs Won'tTOPIK 1 — The semantic split that Korean forces you to make: 안 negates choice or plain fact ('doesn't / won't'), while 못 negates ability blocked by circumstance ('can't, though I might want to').