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Necessity & Obligation

-(으)면 안 되다 - Must not

-(으)면 안 되다 expresses prohibition or that something is not allowed. It means "must not," "should not," "cannot," or "not allowed to."

Structure

Verb stem + -(으)면 안 되다

Breakdown:

  • -(으)면: If (conditional)
  • 안 되다: Not okay/Not acceptable

Literal meaning: "If (you do)... it's not okay"

Conjugation Rules

After Vowel or ㄹ: -면

No consonant at end:

  • 가다 → 가면 안 돼요 (must not go)
  • 오다 → 오면 안 돼요 (must not come)
  • 마시다 → 마시면 안 돼요 (must not drink)

After ㄹ (drop ㄹ):

  • 만들다 → 만들면 안 돼요 (must not make)
  • 팔다 → 팔면 안 돼요 (must not sell)

After Consonant: -으면

Consonant at end:

  • 먹다 → 먹으면 안 돼요 (must not eat)
  • 읽다 → 읽으면 안 돼요 (must not read)
  • 듣다 → 듣으면 안 돼요 (must not listen)

하다 Verbs: -하면

All 하다 verbs:

  • 하다 → 하면 안 돼요 (must not do)
  • 공부하다 → 공부하면 안 돼요 (must not study)
  • 사용하다 → 사용하면 안 돼요 (must not use)

Politeness Levels

Formal (합니다체)

  • 가면 안 됩니다 (must not go)
  • 먹으면 안 됩니다 (must not eat)
  • 하면 안 됩니다 (must not do)

Polite (해요체)

  • 가면 안 돼요 (must not go)
  • 먹으면 안 돼요 (must not eat)
  • 하면 안 돼요 (must not do)

Casual (반말)

  • 가면 안 돼 (must not go)
  • 먹으면 안 돼 (must not eat)
  • 하면 안 돼 (must not do)

Past Tense

Was not allowed / Wasn't supposed to:

  • 가면 안 됐어요 (wasn't allowed to go)
  • 먹으면 안 됐어요 (wasn't allowed to eat)
  • 하면 안 됐어요 (wasn't supposed to do)

Usage: Expressing past prohibition or rules

Common Usage

Rules and Regulations

Public rules:

  • 여기서 담배 피우면 안 돼요 (You can't smoke here)
  • 사진 찍으면 안 돼요 (You can't take pictures)
  • 주차하면 안 돼요 (You can't park here)
  • 들어가면 안 돼요 (You can't enter)

School/Work Rules

Institutional rules:

  • 지각하면 안 돼요 (You mustn't be late)
  • 복사하면 안 돼요 (You can't copy)
  • 휴대폰 사용하면 안 돼요 (You can't use your phone)
  • 떠들면 안 돼요 (You can't make noise)

Parental/Authority Commands

Instructions from authority:

  • 늦게까지 놀면 안 돼요 (You can't play until late)
  • 과자 많이 먹으면 안 돼요 (You can't eat too many snacks)
  • 거짓말하면 안 돼요 (You mustn't lie)
  • 포기하면 안 돼요 (You mustn't give up)

Question Form

Asking if Something is Allowed

Pattern: -(으)면 안 돼요?

Examples:

  • 여기 앉으면 안 돼요? (Can't I sit here?)
  • 이거 먹으면 안 돼요? (Can't I eat this?)
  • 사진 찍으면 안 돼요? (Can't I take pictures?)
  • 들어가면 안 돼요? (Can't I enter?)

Usage: Checking if something is prohibited

Softer Question Form

More polite way to ask:

  • 여기 앉아도 돼요? (May I sit here?)
  • Rather than: 여기 앉으면 안 돼요?

Common Signs and Warnings

Public Signs

  • 금연 (No smoking) → 담배 피우면 안 됩니다
  • 사진 촬영 금지 → 사진 찍으면 안 됩니다
  • 출입 금지 → 들어가면 안 됩니다
  • 주차 금지 → 주차하면 안 됩니다
  • 음식물 반입 금지 → 음식 가져오면 안 됩니다

Safety Warnings

  • 만지면 안 돼요 (Don't touch)
  • 열면 안 돼요 (Don't open)
  • 가까이 가면 안 돼요 (Don't go close)
  • 뛰면 안 돼요 (Don't run)

Contrast with Similar Expressions

-(으)면 안 되다 vs -지 마세요

-(으)면 안 되다: Must not (prohibition, rule-based)

  • 가면 안 돼요 (You must not go / It's not allowed)
  • → Stating a rule or prohibition

-지 마세요: Don't (direct command)

  • 가지 마세요 (Don't go)
  • → Direct imperative command

Nuance difference:

  • -(으)면 안 되다: More about rules/consequences
  • -지 마세요: More direct command

-(으)면 안 되다 vs -지 않아도 되다

-(으)면 안 되다: Must not (forbidden)

  • 가면 안 돼요 (You must not go)
  • → Action is prohibited

-지 않아도 되다: Don't have to (optional)

  • 안 가도 돼요 (You don't have to go)
  • → Action is not required but allowed

Key difference: Prohibition vs Lack of obligation

Common Expressions

Health and Safety

  • 술 마시면 안 돼요 (You mustn't drink alcohol)
  • 운전하면 안 돼요 (You can't drive)
  • 밖에 나가면 안 돼요 (You can't go outside)
  • 아프면 운동하면 안 돼요 (You mustn't exercise if you're sick)

Social Etiquette

  • 큰 소리로 말하면 안 돼요 (You can't speak loudly)
  • 먼저 먹으면 안 돼요 (You can't eat first)
  • 무례하게 행동하면 안 돼요 (You mustn't behave rudely)
  • 약속 어기면 안 돼요 (You mustn't break promises)

Advice/Warnings

  • 포기하면 안 돼요 (You mustn't give up)
  • 늦으면 안 돼요 (You can't be late)
  • 잊으면 안 돼요 (You mustn't forget)
  • 실수하면 안 돼요 (You can't make mistakes)

Emphasis and Softening

Strong Prohibition: 절대

Absolutely must not:

  • 절대 가면 안 돼요 (You absolutely must not go)
  • 절대 말하면 안 돼요 (You absolutely can't tell)
  • 절대 포기하면 안 돼요 (You absolutely mustn't give up)

Softening: 좀

More gentle:

  • 좀 늦으면 안 돼요? (Can't I be a bit late?)
  • 좀만 사용하면 안 돼요? (Can't I use it just a little?)

Example Dialogues

Dialogue 1: At Museum

A: 여기서 사진 찍어도 돼요?
(May I take pictures here?)

B: 아니요, 사진 찍으면 안 돼요.
(No, you can't take pictures.)

Dialogue 2: At Home

A: 엄마, 게임 좀 더 해도 돼요?
(Mom, can I play games a bit more?)

B: 안 돼. 숙제 먼저 해야지. 숙제 안 하면 안 돼.
(No. You need to do homework first. You can't not do homework.)

Dialogue 3: At Work

A: 이 서류 내일 내도 돼요?
(Can I submit this document tomorrow?)

B: 안 돼요. 오늘까지예요. 늦으면 안 돼요.
(No. It's due today. You can't be late.)

Common Mistakes

❌ Incorrect: 하지 않으면 안 돼요

Double negative - changes meaning to "must do"

✅ Correct: 하면 안 돼요

Proper prohibition form

❌ Incorrect: 가면 안 하다

Using 하다 instead of 되다

✅ Correct: 가면 안 되다

Must use 되다

With Nouns: 이/가 되다

Noun + 이/가 되면 안 되다

Pattern for noun phrases:

  • 문제가 되면 안 돼요 (It mustn't become a problem)
  • 비밀이 되면 안 돼요 (It can't be a secret)
  • 방해가 되면 안 돼요 (It mustn't be a disturbance)

Summary Table

Verb-(으)면 안 되다 (Polite)CasualMeaning
가다가면 안 돼요가면 안 돼Must not go
먹다먹으면 안 돼요먹으면 안 돼Must not eat
하다하면 안 돼요하면 안 돼Must not do
오다오면 안 돼요오면 안 돼Must not come
사용하다사용하면 안 돼요사용하면 안 돼Must not use

Key Takeaways

✅ Expresses prohibition: "You must not / can't"
✅ States rules and restrictions: Not allowed
✅ After vowel/ㄹ: -면 안 되다
✅ After consonant: -으면 안 되다
✅ Different from -지 마세요: Rules vs Direct command
✅ Opposite of -아/어도 되다: Not allowed vs Allowed

-(으)면 안 되다 is essential for expressing prohibitions, rules, and restrictions, commonly used in signs, regulations, and when giving instructions about what's not allowed.