In English, you say "I have to go" or "I must study." Korean expresses the same idea with one reliable pattern:
Verb stem + 아야/어야 하다: have to, must, should
How to form it
The connector ~아야/어야 follows the same vowel harmony rule as ~아서/어서:
- If the verb stem contains ㅏ or ㅗ → add 아야
- All other vowels → add 어야
- 하다 verbs → 해야
| Verb | Stem ends in | Form |
|---|---|---|
| 가다 (go) | ㅏ (vowel) | 가아야 → 가야 |
| 먹다 (eat) | ㅓ (vowel) | 먹어야 |
| 자다 (sleep) | ㅏ | 자아야 → 자야 |
| 오다 (come) | ㅗ | 와야 |
| 공부하다 (study) | 하다 | 공부해야 |
Note: 가아야 contracts to 가야 in natural speech.
In sentences (polite)
공부해야 해요. I have to study. 지금 가야 해요. I have to go now. 이걸 먹어야 해요. I have to eat this. 일찍 일어나야 해요. I have to wake up early. 돈을 내야 해요. I have to pay.
The "double 해". 해야 해요
공부해야 해요 ends in 해야 해요: two 해's. This looks strange but it's correct and very common. Don't try to simplify it. Native speakers say it this way.
Negative: don't have to vs must not
안 해도 돼요: don't have to (it's okay not to) 거기 안 가도 돼요. You don't have to go there.
~면 안 돼요: must not (prohibition) 거기 가면 안 돼요. You must not go there. The difference is critical:
- Don't have to = optional, no obligation
- Must not = prohibited, forbidden
안 가도 돼요. You don't have to go. (free choice) 가면 안 돼요. You must not go. (it's wrong/not allowed)
Stronger and weaker forms
~야 되다: slightly less formal, same meaning as ~야 하다 Koreans use 되다 and 하다 interchangeably here.
가야 해요. = 가야 돼요. Both mean "I have to go."
~아야/어야 하는데...: "I have to [but]..." The ~는데 ending adds "but" or implication of a problem:
지금 가야 하는데.. I have to go now, but. (implies you don't want to / something is stopping you)
Common questions
꼭 해야 해요? Do I really have to do it? 꼭 (kkok) = necessarily / really / for sure. Use it to question whether something is truly mandatory.
언제까지 해야 해요? By when do I have to do it?
Practice sentences
내일까지 이 보고서를 제출해야 해요. I have to submit this report by tomorrow. 비타민을 매일 먹어야 해요. You have to take vitamins every day. 여기서는 조용히 해야 해요. You have to be quiet here. 휴가 전에 일을 끝내야 해요. I have to finish the work before vacation.
Obligation patterns come up in almost every real-world conversation: scheduling, rules, advice, instructions. This pattern pairs naturally with ~ㄹ/을 수 있다 (can) from the previous lesson.
For the full set of grammar patterns at this level, including practice exercises with answer keys, see my Korean Grammar Essentials workbook. A structured Korean course drills patterns like this in context, not in isolation.