Must and Should Expressions¶
Quick Reference
- -아/어야 하다/되다: must, have to, should (obligation/necessity)
- -면 안 되다: must not, cannot (prohibition)
- -아/어야 하다 is stronger obligation than -아/어야 되다
- Attach to verb stems, follow vowel harmony rules
Detailed Explanation¶
-아/어야 하다/되다 (Must/Have to/Should)¶
These patterns express obligation, necessity, or strong recommendation.
Formation: - Verb stem + -아/어야 + 하다/되다 - Follow standard vowel harmony (ㅏ/ㅗ → 아야, all others → 어야) - 하다 verbs → 해야
하다 vs 되다: - -아/어야 하다: Stronger obligation, external requirement - -아/어야 되다: Slightly softer, more conversational
Conjugation:
가다 → 가야 하다/되다 (must go)
먹다 → 먹어야 하다/되다 (must eat)
공부하다 → 공부해야 하다/되다 (must study)
-면 안 되다 (Must Not/Cannot)¶
Expresses prohibition or strong warning against an action.
Formation: - Verb stem + -면 안 되다 - Literally: "if you do X, it won't do/work"
Examples:
가다 → 가면 안 되다 (must not go)
먹다 → 먹으면 안 되다 (must not eat)
말하다 → 말하면 안 되다 (must not speak)
When to Use¶
-아/어야 하다/되다: - Giving advice or recommendations - Expressing personal obligations - Stating rules or requirements - Describing necessary conditions
-면 안 되다: - Stating prohibitions or rules - Warning against dangerous actions - Expressing things that are not allowed - Setting boundaries
Examples¶
Obligations: - 내일 학교에 가야 해요. (I have to go to school tomorrow.) - 숙제를 해야 돼요. (I need to do my homework.) - 약을 먹어야 해요. (You should take medicine.) - 한국어를 열심히 공부해야 해요. (You must study Korean diligently.)
Prohibitions: - 여기서 담배를 피우면 안 돼요. (You must not smoke here.) - 시험 중에 말하면 안 돼요. (You cannot talk during the exam.) - 이 물을 마시면 안 돼요. (You must not drink this water.) - 늦게 자면 안 돼요. (You shouldn't go to bed late.)
Dialogue:
A: 내일 약속이 있어요?
B: 네, 병원에 가야 해요.
A: 아파요?
B: 감기 때문에 의사를 만나야 해요.
A: Do you have plans tomorrow?
B: Yes, I have to go to the hospital.
A: Are you sick?
B: I need to see a doctor because of a cold.
Practice¶
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Complete: 저는 매일 운동을 ______. (I have to exercise every day.)
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Complete: 도서관에서 ______ 안 돼요. (You must not be loud in the library.) [시끄럽다]
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Translate: You must wake up early tomorrow.
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Complete: 건강하려면 야채를 많이 ______. (To be healthy, you must eat lots of vegetables.) [먹다]
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Complete: 수업 시간에 전화를 ______ 안 돼요. (You cannot use your phone during class.) [사용하다]
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Translate: I need to meet my friend at 3 o'clock.
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Complete: 비가 오니까 우산을 ______. (Since it's raining, you should bring an umbrella.) [가지고 가다]
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Complete: 시험 중에 ______ 안 돼요. (You must not cheat during the exam.) [컨닝하다]
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Create a sentence using -아/어야 해요 about something you need to do this week.
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Create a sentence using -면 안 돼요 about a rule in your home or workplace.