아/어/여야 하다/되다 (must, have to)

At its core, this grammar combines two parts. First, you take a verb and connect it with the 아/어/여 ending. Then, you attach 야, followed by the verbs 하다 (to do) or 되다 (to become). The literal translation is something like "if you do [Action], only then does it work out" or "only then is it okay." It creates a condition that must be met. If the condition isn't met, the result isn't valid. Think of it like a key and a lock. You 야 (must) have the key to open the door. Without the key, no entry! Interestingly, there is a tiny difference between 하다 and 되다. 하다 feels a bit more formal and objective. You might see it in written rules or hear it in a speech. 되다 is the cool cousin. It is much more common in daily spoken Korean. When you are chatting with friends or ordering food, 되다 is usually your best bet. Both mean "must," so don't sweat the choice too much early on. Just remember that this pattern always points to a necessity. It isn't just a suggestion; it’s a requirement.

1. 1Creating this grammar is a simple three-step process. If you already know how to conjugate the present tense (아/어/여요), you are 90% of the way there!
2. 2Find the verb stem. Drop the 다 from any verb. For 가다 (to go), the stem is 가.
3. 3Choose the right connector.
4. 4If the last vowel is ㅏ or ㅗ, use -아야.
5. 5If the last vowel is anything else, use -어야.
6. 6For 하다 verbs, they always change to 해야.
7. 7Add the final verb. Attach 하다 or 되다 and conjugate it to your desired politeness level.
8. 8Let's look at some quick examples:
9. 9가다 (to go) → 가 + 아야 + 해요 = 가야 해요 (must go).
10. 10먹다 (to eat) → 먹 + 어야 + 돼요 = 먹어야 돼요 (must eat).
11. 11공부하다 (to study) → 공부해야 + 돼요 = 공부해야 돼요 (must study).
12. 12쓰다 (to write/use) → 써야 + 해요 = 써야 해요 (must write).

Use this grammar whenever there is no other way around a situation. It is perfect for daily routines that aren't optional. For example, "I must go to work" or "I must wake up early." It’s also the go-to for giving strong advice. If your friend is sick, you can say 병원에 가야 돼요 (You must go to the hospital). It shows you care because the necessity is high.

In social scenarios, it is very useful. Imagine you are at a restaurant that is pay-first. The waiter might say 먼저 결제해야 돼요 (You must pay first). Or maybe you are at a job interview. You might say 열심히 일해야 해요 (I must work hard) to show your dedication. Use it for rules and laws too. "You must wear a seatbelt" or "You must have a passport." It acts like a clear boundary. It’s the grammar equivalent of saying "This is the way it has to be." Even when you are talking to yourself, like "I really must clean my room," this is the pattern you use. It adds that sense of "no excuses" to your Korean.

Be careful with the tone! Because 아/어/여야 하다 is quite strong, it can sound a bit demanding if you use it with someone much older or in a higher position. Telling your boss 이거 해야 돼요 (You must do this) might get you some side-eye. It’s better to use more polite suggestions like -(으)시면 좋겠어요 (It would be good if you...) in those cases.

Also, don't use this for predictions. In English, we sometimes say "It must be raining" to mean "I bet it's raining." In Korean, this grammar doesn't work that way. For guesses, you should use -(으)ㅁ에 틀림없다 or -겠다. 아/어/여야 하다 is only for obligations and requirements. If there is no "duty" involved, skip this rule. Using it for a guess would make you sound like you are commanding the rain to fall, which is a cool superpower, but not what you want to say! Finally, avoid using it for things that are just "nice to do." If it’s just a casual suggestion, stick to -(으)면 좋아요 (It's good if...). Save the "must" for the real deal.

One big trap is the spelling of 되다. In the present tense, it becomes 돼요, not 되요. This is a classic mistake that even native speakers make in texts. Think of the ㅐ as the "action" version. Another common slip-up is forgetting the 야. Some learners just say 가 해요, which doesn't mean anything. You need that 야 to bridge the gap and create the "must" meaning.

Don't forget irregular verbs. For example, 듣다 (to listen) becomes 들어야 해요. If you forget to change the ㄷ to ㄹ, it sounds quite awkward. Also, watch out for the negative form. If you want to say "must not," don't just put 안 in front. That would mean "don't have to." To say "must not," you actually use a completely different structure: -(으)면 안 되다. It’s like a grammar trap door. If you try to force a negative into 아/어/여야 하다, it usually ends up sounding messy. Keep it simple: use this rule for what you do have to do, and use the other rule for what is forbidden.

Sometimes this rule gets confused with -(으)ㄹ게요 (I will). While both talk about the future, -(으)ㄹ게요 is a promise or a choice. 아/어/여야 해요 is a necessity. If you say 갈게요, you are saying "I'll go (because I want to/I'm promising)." If you say 가야 돼요, you are saying "I'm going because I have to." It's the difference between volunteering and being drafted!

Another close relative is -아/어/여야겠다. Adding that 겠 at the end makes it feel like a personal realization or a firm decision you just made. 공부해야 돼요 sounds like a general fact (I have an exam). 공부해야겠어요 sounds like you just looked at your bad grades and told yourself, "Okay, I really need to start studying now." One is a state of obligation, the other is the moment you accept that obligation. Think of it like a lightbulb moment. Finally, don't confuse it with -고 싶다 (want to). We often have to do things we don't want to do. You might 가야 돼요 (must go) even if you don't 가고 싶어요 (want to go). That’s just adulting, Korean style.