If -아/어도 되다 is how Korean grants permission, then -(으)면 안 되다 is how it takes permission away. It's the everyday way to say "you must not," "you're not allowed to," "don't." And like its positive twin, it isn't a special modal word — it's transparent once you read its parts: the conditional -(으)면 ("if you do X") plus 안 되다 ("it does not become OK"). Put together: "if you do X, that doesn't fly" → X is forbidden. Getting comfortable with this decoding is what keeps you from crossing its wires with "don't have to," the mistake English guarantees.
The form: verb/adjective + -(으)면 + 안 되다
Attach the conditional ending -(으)면 to the stem, then 안 되다:
- Consonant stem → -으면: 먹다 → 먹으면, 늦다 → 늦으면
- Vowel or ㄹ stem → -면: 가다 → 가면, 만지다 → 만지면, 열다 → 열면
여기서 담배를 피우면 안 돼요.
yeogiseo dambaereul piumyeon an dwaeyo
You must not smoke here.
수업에 늦으면 안 돼요.
sueobe neujeumyeon an dwaeyo
You mustn't be late to class.
이거 만지면 안 돼.
igeo manjimyeon an dwae
Don't touch this. (casual, banmal)
It works with descriptive verbs (adjectives) too, expressing a state that mustn't come about:
방이 너무 더우면 안 돼요.
bang-i neomu deoumyeon an dwaeyo
The room mustn't get too hot.
It is the exact mirror of -아/어도 되다
The cleanest way to hold this pattern in mind is to line it up against permission. -아/어도 되다 ("even if you do X, it's fine") allows; -(으)면 안 되다 ("if you do X, it's not fine") forbids. Same verb 되다, opposite verdict.
사진 찍어도 돼요.
sajin jjigeodo dwaeyo
You may take photos.
사진 찍으면 안 돼요.
sajin jjigeumyeon an dwaeyo
You must not take photos.
That mirror is why signs, rules, and warnings lean on -(으)면 안 되다 so heavily: it is the plain, direct way to state that something is off-limits.
도서관에서 떠들면 안 돼요.
doseogwaneseo tteodeulmyeon an dwaeyo
You mustn't make noise in the library.
약속을 잊으면 안 돼요.
yaksogeul ijeumyeon an dwaeyo
You mustn't forget the promise.
The obligation square: four corners, don't cross the wires
The 되다 family maps out a neat square, and the whole point of learning it is to keep the four corners apart — because English "don't have to" and "must not" are almost the same words, while their Korean equivalents are built oppositely.
| English | Korean | Force |
|---|---|---|
| must do | 해야 돼요 | required |
| must NOT do | 하면 안 돼요 | forbidden |
| don't HAVE to do | 안 해도 돼요 | optional (no requirement) |
| may do | 해도 돼요 | permitted |
The dangerous pair is 하면 안 돼요 ("must not do") versus 안 해도 돼요 ("don't have to do"). The first is a ban; the second is a free pass. 들어가면 안 돼요 forbids entering; 안 들어가도 돼요 simply says entering isn't required. English speakers routinely say one when they mean the other — see -지 않아도 되다 for the "don't have to" side in full.
-(으)면 안 되다 vs. -지 마세요
Both express "don't," but they are different speech acts. -(으)면 안 되다 states a rule — "doing X is not allowed" — and can describe a general prohibition, someone else's situation, or a warning. The imperative -지 마세요 is a direct command to the listener — "don't do X" — aimed straight at the person in front of you.
여기 주차하면 안 돼요.
yeogi juchahamyeon an dwaeyo
You can't park here. (stating the rule)
여기 주차하지 마세요.
yeogi juchahaji maseyo
Please don't park here. (telling you directly)
A posted sign or a general policy tends toward 하면 안 돼요; a person stopping you in the moment tends toward 하지 마세요. They overlap heavily, but the rule-versus-command flavor is real.
Softening a prohibition
Telling someone flatly that they can't do something is face-threatening, so in polite situations Koreans rarely fire a bare 하면 안 돼요 at a stranger or a superior. Two moves soften it. First, add the subject honorific -(으)시- to the verb — 하시면 안 돼요 / 하시면 안 됩니다 shows respect to the very person you're restraining. Second, hedge the whole thing with -(으)ㄹ 것 같다 ("it seems...") so it lands as a gentle "I'm afraid that won't work" rather than a hard "no."
여기 들어가시면 안 됩니다.
yeogi deureogasimyeon an doemnida
You may not go in here. (formal, with honorific 시 — a sign or a staff member)
죄송하지만, 지금은 좀 안 될 것 같아요.
joesonghajiman, jigeumeun jom an doel geot gatayo
I'm sorry, but right now it might not be OK. (a softened refusal)
The blunt 하면 안 돼 (banmal) is fine among close friends or for a firm parental "no," but with strangers the honorific and the hedge do real social work — a plain prohibition can feel like an accusation.
Common Mistakes
1. Building a prohibition with ×-지 않아야 하다. Learners who know -아/어야 하다 ("must") sometimes negate the verb and produce a stiff, unnatural "must not." Real Korean uses -(으)면 안 되다.
❌ 여기서 담배를 피우지 않아야 해요.
Stilted and unnatural — Koreans say 피우면 안 돼요 for 'you must not smoke.'
✅ 여기서 담배를 피우면 안 돼요.
yeogiseo dambaereul piumyeon an dwaeyo
You must not smoke here.
2. Confusing "must not" with "don't have to." A "no entry" sign means 들어가면 안 돼요 (forbidden). Saying 안 들어가도 돼요 accidentally says entering is merely optional.
❌ 안 들어가도 돼요.
an deureogado dwaeyo
When you mean 'you must not enter,' this misfires — it means 'you don't have to enter.'
✅ 들어가면 안 돼요.
deureogamyeon an dwaeyo
You must not enter.
3. Spelling ×되요 instead of 돼요. As everywhere with 되다, the polite present is 돼요 (from 되어요), never ×되요.
❌ 만지면 안 되요.
Wrong spelling — 되 needs 어: it must be 안 돼요.
✅ 만지면 안 돼요.
manjimyeon an dwaeyo
You mustn't touch it.
4. Dropping the 으 after a consonant stem. 먹다 is a consonant stem, so the conditional is 먹으면, not ×먹면.
❌ 이거 먹면 안 돼요.
Wrong — a consonant stem needs -으면: 먹으면.
✅ 이거 먹으면 안 돼요.
igeo meogeumyeon an dwaeyo
You mustn't eat this.
Key Takeaways
- -(으)면 안 되다 = "if you do X, it's not OK" = prohibition ("must not, not allowed").
- It is the exact negative of -아/어도 되다: same 되다, opposite verdict.
- On the obligation square, keep 하면 안 돼요 (forbidden) strictly apart from 안 해도 돼요 (optional) — the classic English trap.
- It states a rule; the direct command "don't" is -지 마세요. Both are common; the flavor differs.
- Spell it 안 돼요 (from 되어요), and remember -으면 after consonant stems.
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Start learning Korean→Related Topics
- -아/어도 되다: May / It's OK ToTOPIK 2 — The permission construction — 'you may, it's OK to, you're allowed to' — built from -아/어도 ('even if you do X') plus 되다 ('it becomes acceptable'), with 괜찮다 and 좋다 as free swaps.
- -지 않아도 되다 / -(으)ㄹ 필요 없다: Don't Have ToTOPIK 3 — How to waive an obligation — 'you don't have to, you needn't' — the negation of NECESSITY, and why it is the polar opposite of the prohibition 'must not.'
- -(으)면 되다: You Just Have To / That's All It TakesTOPIK 3 — The sufficiency construction — 'if you do X, that's all it takes' — the reassuring member of the 되다 family, carefully kept apart from 'must' (-아/어야 되다) and 'may' (-아/어도 되다).
- -아/어야 하다 / -아/어야 되다: Must / Have ToTOPIK 2 — The core Korean 'must / have to' construction — its vowel harmony, the near-interchangeable 하다 vs 되다, the 돼요 spelling, and its 'only if' inner logic.