| meaning | pattern | example |
|---|---|---|
| must, have to | -아/어야 해요 / 돼요 | 가야 돼요 — I have to go |
| may, it's okay to | -아/어도 돼요 | 먹어도 돼요? — May I eat? |
| must not | -(으)면 안 돼요 | 찍으면 안 돼요 — You mustn't take (photos) |
| don't have to | 안 -아/어도 돼요 | 안 가도 돼요 — You don't have to go |
The 아/어 part follows the same rules as the present tense: 하다 → 해야, 가다 → 가야, 먹다 → 먹어야. 해야 돼요 is more common in speech, 해야 해요 slightly more neutral.