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Grammar / Level 1 / Lesson 26

ㄹ/을 수 있다 and 아/어야 하다: can, must and needn't

By Daniel Buckley · 11 minute read · TOPIK 1

Vocabulary

  1. 수 - a way, a means
  2. 필요 - need
  3. 되다 - to be OK
  4. 운전하다 - to drive
  5. 약 - medicine
  6. 숙제 - homework
  7. 예약하다 - to book
  8. 기다리다 - to wait
  9. 혼자 - alone
  10. 걱정하다 - to worry

Eat with Korean friends and someone will ask 매운 음식 먹을 수 있어요?, can you eat spicy food? Literally, it asks whether a way to eat spicy food exists.

Korean has no verb for "can" or "must". It says them with ordinary words: "a way exists" for can, "only if you do it" for must. Keep those literal meanings in mind and the negatives will make sense.

Can: ㄹ/을 수 있다

수 is a noun meaning a way or a means. It can't stand alone, so a verb always comes before it, in the same ㄹ/을 form you know from ㄹ/을 거예요 and ㄹ/을 때. Then 있다 says the way exists, and 없다 says it doesn't.

Making ㄹ/을 수 있다

  • Stem ends in a vowel: add ㄹ 수 있다.가다 → 갈 수 있어요마시다 → 마실 수 있어요
  • Stem ends in a consonant: add 을 수 있다.먹다 → 먹을 수 있어요읽다 → 읽을 수 있어요
  • Stem ends in ㄹ: the ㄹ is already there, so add 수 있다.만들다 → 만들 수 있어요
  • Can't: change 있다 to 없다.가다 → 갈 수 없어요먹다 → 먹을 수 없어요

Pick a verb

가다가갈 수 있어요

  1. 저는 한국어를 할 수 있어요.

    I can do Korean.

  2. 혼자 갈 수 있어요.

    (I) can go alone.

  3. 여기에서 표를 살 수 있어요.

    Here (you) can buy ticket.

  4. 매운 음식은 먹을 수 없어요.

    Spicy food (I) can't eat.

  5. 오늘은 만날 수 없어요.

    Today (we) can't meet.

  6. 어제는 운전할 수 없었어요.

    Yesterday (I) couldn't drive.

Example 6 puts the past on 없다, at the end. For "could" and "couldn't", the verb before 수 stays as it is.

※ 못 가요 and 갈 수 없어요 both say you can't go. In conversation 못 is usually the more common of the two, and 수 없다 sounds firmer.

It might happen

"A way exists" isn't only about ability. It also says that something is possible, where English reaches for "might" or "could". Context tells you which one you're reading.

  1. 내일 비가 올 수 있어요.

    Tomorrow rain might come.

  2. 길이 막혀서 늦을 수 있어요.

    Road is blocked, so (I) might be late.

  3. 그럴 수 있어요.

    (It) can be like that.

Example 3 is a stock phrase. It's what you say when someone admits a mistake and you're letting it go: fair enough, these things happen.

Must: 아/어야 하다, 아/어야 되다

The 야 here means "only if". 가야 돼요 is literally "only if (I) go, (it's) OK": nothing else will do. English hears that as "have to" or "must".

Making 아/어야 하다 and 아/어야 되다

  • Take the 해요 form, drop 요, add 야 해요.가요 → 가야 해요먹어요 → 먹어야 해요해요 → 해야 해요
  • Or add 야 돼요. The meaning is the same.가요 → 가야 돼요먹어요 → 먹어야 돼요

Pick a verb

가다가요가야 해요

해요 and 돼요 are interchangeable here. 돼요 is a little more common in speech.

  1. 오늘은 숙제를 해야 해요.

    Today (I) have to do homework.

  2. 내일 일찍 일어나야 돼요.

    Tomorrow (I) have to get up early.

  3. 지금 집에 가야 돼요.

    Now (I) have to go home.

  4. 약을 먹어야 해요.

    (I) have to eat medicine.

  5. 식당을 예약해야 돼요.

    (We) have to book restaurant.

  6. 어제는 회사에 가야 했어요.

    Yesterday (I) had to go to work.

Example 4 isn't a joke: Korean eats medicine. Example 6 shows the past, which goes on the final 하다, the same as 수 있었어요.

Need and needn't: ㄹ/을 필요가 있다, 없다

필요 is a noun meaning need, and it sits where 수 sat: "a need to go doesn't exist". The 가 is the subject particle, and in speech it often drops, giving 갈 필요 없어요.

  1. 오늘은 회사에 갈 필요가 없어요.

    Today (I) don't need to go to work.

  2. 돈을 낼 필요가 없어요.

    (You) don't need to pay money.

  3. 오래 기다릴 필요가 없어요.

    (You) don't need to wait long.

  4. 걱정할 필요 없어요.

    (You) don't need to worry.

The positive, ㄹ/을 필요가 있다, says the need does exist. It's softer than 아/어야 돼요, which says you must. It also sounds a little formal, closer to "it's necessary to", so it suits advice and discussion more than your own errands.

  1. 이 식당은 미리 예약할 필요가 있어요.

    This restaurant (you) need to book in advance.

  2. 이 문제는 다시 생각할 필요가 있어요.

    This problem (we) need to think about again.

For "needn't", you'll hear another version even more often: 안 가도 돼요. That's 아/어도 plus 되다, "even if (you) don't go, (it's) OK". Lesson 55 covers it properly.

  1. 내일 시험이 있어서 오늘 공부___.

    I have an exam tomorrow, so I have to study today.

  2. 오늘은 토요일이라서 학교에 ___.

    It's Saturday, so I don't need to go to school.

  3. 다리가 아파서 ___.

    My leg hurts, so I can't walk.

  4. 길이 막혀서 ___.

    The road is blocked, so I might be late.

Listen and type

1 / 3

Play it as often as you like.

In a conversation

A

내일 같이 점심 먹을 수 있어요?

Tomorrow together lunch can eat?

B

미안해요. 내일은 회사에 가야 돼요.

Sorry. Tomorrow (I) have to go to work.

A

토요일에도 일해야 돼요?

On Saturday too (you) have to work?

B

네, 요즘 바빠서 쉴 수 없어요.

Yes, these days busy, so (I) can't rest.

A

그럼 일요일은 어때요? 제가 식당을 예약해야 돼요?

Then Sunday how is? I restaurant have to book?

B

아니요, 예약할 필요 없어요.

No, need to book doesn't exist.

Common mistakes

  1. 매운 음식을 먹을 수 안 있어요.

    매운 음식을 먹을 수 없어요.

    있다 has its own opposite. Use 없다, not 안 있다.

  2. 오늘은 학교에 안 가야 해요.

    오늘은 학교에 갈 필요가 없어요.

    안 가야 해요 means you have to stay away. For "don't have to", it's the need that gets denied.

  3. 어제 회사에 갔어야 해요.

    어제 회사에 가야 했어요.

    "Had to" puts the past on the final 하다.

One sentence in each group is wrong. Tap it.

Check yourself

Quick check

1 / 6

혼자 ___ 수 있어요. (가다) I can go alone.

The stem ends in a vowel, so ㄹ attaches to it.

Summary

ㄹ/을 수 있어요 forms
DictionaryStemㄹ/을 수 있어요
가다가갈 수 있어요
먹다먹먹을 수 있어요
만들다만들만들 수 있어요
듣다듣들을 수 있어요
돕다돕도울 수 있어요
쓰다쓰쓸 수 있어요
아/어야 해요 forms
Dictionary해요아/어야 해요
가다가요가야 해요
먹다먹어요먹어야 해요
하다해요해야 해요
듣다들어요들어야 해요
돕다도와요도와야 해요
쓰다써요써야 해요

The negatives

  • Can't: 있다 becomes 없다.갈 수 없어요
  • Need, needn't: 필요가 있다 and 필요가 없다.갈 필요가 있어요갈 필요가 없어요

Now you can say

  1. 한국어를 조금 할 수 있어요.

    (I) can do Korean a little.

  2. 이제 집에 가야 돼요.

    Now (I) have to go home.

  3. 걱정할 필요 없어요.

    (You) don't need to worry.

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