-아/어서는 안 되다
Must Not, Should Not
-아/어서는 안 되다 expresses prohibition, meaning "must not," "should not," or "it is not allowed to."
How It Works
This pattern is a formal and often emphatic way to express prohibition. It's commonly found in written rules, warnings, and formal speech.
Conjugation:
1. Verb/adjective stem ends in ㅏ or ㅗ: Add -아서는 안 되다.
- 가다 → 가서 + 는 안 되다 → 가서는 안 되다
- 보다 → 봐서 + 는 안 되다 → 봐서는 안 되다
2. Verb/adjective stem ends in any other vowel: Add -어서는 안 되다.
- 먹다 → 먹어서 + 는 안 되다 → 먹어서는 안 되다
- 읽다 → 읽어서 + 는 안 되다 → 읽어서는 안 되다
3. 하다 verbs: Becomes 해서는 안 되다.
- 공부하다 → 공부해서 + 는 안 되다 → 공부해서는 안 되다
Comparison with similar patterns:
- vs. -면 안 되다: Both mean "must not." -면 안 되다 is more common in everyday conversation. -아/어서는 안 되다 often carries a stronger, more formal nuance, saying that the action itself is not acceptable. It's frequently used for official rules or moral principles.
- vs. -지 말다 (e.g., -지 마세요): -지 말다 is a direct negative command telling someone not to do something. -아/어서는 안 되다 is a declarative statement about what is permissible or not. For example, a sign would say "들어가서는 안 됩니다" (One must not enter), while a person would say to their friend "들어가지 마" (Don't go in).
Examples (4)
- 박물관 안에서 사진을 찍어서는 안 됩니다.
You must not take pictures inside the museum.
Word by Word: Inside the museum, taking pictures is not okay.
- 다른 사람의 물건을 함부로 만져서는 안 돼요.
You shouldn't touch other people's belongings carelessly.
Word by Word: Other people's belongings carelessly touching is not okay.
- 어떤 경우에도 거짓말을 해서는 안 된다.
You must not lie under any circumstances.
Word by Word: In any case, lying is not okay.
This example shows a strong moral prohibition, a common use for this pattern.
- 아무리 화가 나도 폭력을 사용해서는 안 되지요.
No matter how angry you get, you must not use violence, of course.
Word by Word: However angry you get, using violence is not okay.
Common Mistakes
Omitting the particle '는'.
Not Quite여기서 수영해서 안 돼요.Better여기서 수영해서는 안 돼요.The particle '는' is a key part of this grammar pattern. It is a topic particle, so the pattern means 'as for doing it that way, it is not okay'. While it might be dropped in very casual speech, it's grammatically correct and standard to include it.
Using -아서는 after a stem whose last vowel is not ㅏ or ㅗ.
Not Quite교실에서 음식을 먹아서는 안 돼요.Better교실에서 음식을 먹어서는 안 돼요.The last vowel of 먹 is ㅓ, not ㅏ or ㅗ, so the ending is -어서는, not -아서는. Only stems whose last vowel is ㅏ or ㅗ take -아서는, as in 봐서는 and 앉아서는.
Learn This First
To express strong prohibition 'must not', you need causal patterns and negation with 되다.
Related Patterns
- -(으)면 안 되다Must Not, Should Not
A very similar and more common pattern for prohibition. -아/어서는 안 되다 is generally more formal and is common in official rules and moral statements.
- -지 말다Don't Do
This is the negative imperative (command) form, used to directly tell someone not to do something (e.g., -지 마세요). -아/어서는 안 되다 is a declarative statement about a rule or what is permissible, not a direct command.
- -아/어야 되다/하다Have to, Must
This is the opposite of -아/어서는 안 되다. It expresses obligation or necessity ('must do', 'have to do'). Learning them together helps understand the concepts of prohibition and obligation.