Can, Must, May, Seems

Korean Grammar 2

Course 2 · Chapter 9 · Ability, Obligation, Permission and Guessing

🚦 Ability, Obligation, Permission and Guessing — 가능, 의무, 허락, 추측

These are the patterns that let you say what is possible, what you must do, what you may and may not do, and what you think is probably the case. Most are fixed phrases built on the modifier endings of Chapter 7 (-는, -(으)ㄴ, -(으)ㄹ) plus a noun-like word (수, 것, 터) and a closing verb (있다, 같다, 이다). Because the modifier changes with tense and word class, the key to this chapter is Chapter 7's table.

1. Ability and possibility: -(으)ㄹ 수 있다 / 없다

Put the future modifier -(으)ㄹ on the verb, then the pseudo-noun 수, then 있다 ("there is a way") or 없다 ("there is no way"): 할 수 있어요 "I can do it", 먹을 수 없어요 "I can't eat it". ㄹ-stems keep the ㄹ (만들 수 있어요), and Chapter 3's irregulars change before the vowel (추울 수, 들을 수, 도울 수). Only 있다/없다 change for tense: the 수 part stays.

• 저도 그것을 할 수 있어요. "I can do that too."
• 어렸을 때 저는 햄버거 다섯 개를 먹을 수 있었어요. "When I was young I could eat five hamburgers."
• 내년에 캐나다에 갈 수 없을 거예요. "I won't be able to go to Canada next year."
• 문을 열어 줄 수 있어요? "Can you open the door (for me)?" — a polite request.

The particle can follow 수: 수가, 수는, 수도. 그것을 어떻게 할 수가 있어요? "How can you possibly do that?" shows 수가 adding emphasis. The same -(으)ㄹ 수 있다 also means "it is possible that…", which is why 비가 올 수 있어요 is "It may rain".

2. Cannot: 못 and -지 못하다

못 goes directly before the verb and says that something prevented you, or that you could not: 저는 그 동안 공부를 못 했어요 "I couldn't study during that time", 이 셔츠가 너무 작아서 못 입어요 "This shirt is too small, so I can't wear it". The longer form is -지 못하다: 이 문제를 이해하지 못했어요 "I didn't understand this problem". Compare 안 / -지 않다, a plain negative (you don't, by choice or fact): 저는 어제 시험을 안 봤어요 "I didn't take the test yesterday".

	안 / -지 않다	못 / -지 못하다	-(으)ㄹ 수 없다
Meaning	do not (plain negative)	could not (something prevented it)	cannot (general inability)
Example	안 가요	못 가요	갈 수 없어요

The difference between 못 and -(으)ㄹ 수 없다 is subtle: 못 is the colloquial, one-off "couldn't"; -(으)ㄹ 수 없다 is a more general or formal "cannot". Watch the spacing: 잘 못 해요 (can't do it well) differs from 잘못 해요 (do it wrongly / by mistake), and 못하다 written as one word means "be bad at": 나는 수영을 못해 "I'm bad at swimming". 못 is not used with adjectives, so 못 + adjective is not a thing (general knowledge).

3. Must and need to

You met -아/어야 하다 / 되다 in Chapter 6: stem + -아/어야 + 하다 (or 되다) means "have to". 가야 해요 / 가야 돼요 "I must go". Using 되다 instead of 하다 gives exactly the same meaning and is more usual in speech. Past: 그때 열심히 일해야 됐어요 "I had to work hard then"; future: 10분 후에 가야 될 거예요 "We'll have to go in ten minutes". The conversational shortening is -아/어야지(요): 우리가 빨리 가야지! "We have to hurry!", and -아/어야겠다 expresses a decision reached on the spot: 나는 지금 가야겠다 "I'd better go now".

A second phrase is -(으)ㄹ 필요가 있다 / 없다 "there is / is no need to": 나는 밥을 먹을 필요가 있어요 "I need to eat", 제자리에 놓을 필요가 없어요 "You don't need to put it back in its place". 필요하다 itself is an adjective, so the thing needed takes 이/가 and not 을/를: 나는 밥이 필요해요 "I need rice". The negative "must not" has its own form below; "must" is also expressed by a double negative, -지 않으면 안 되다 "it won't do if you don't" (general knowledge).

4. Permission and "don't have to": -아/어도 되다

The ending -아/어도 means "even if". Add 되다 (or 좋다, 괜찮다) and you get permission: 지금 문을 열어도 돼요 "You may open the door now", with the question 제가 일찍 가도 돼요? "May I leave early?". Alternatives with the same sense: 열어도 괜찮아요 and 열어도 좋아요. For 이다 use -(이)어도 / -여도 / -(이)라도. Past: 그때 나가도 되었어요 "It would have been fine if you'd left then"; future: 나가도 될 거예요.

Put a negative before it and you get "don't have to": 내일까지 다 안 해도 돼요 "You don't need to do it all by tomorrow", 빨리 안 가도 돼 "You don't have to go quickly". It is the opposite of -아/어야 하다. The irregular stems change as before -아/어요: 추워도, 몰라도, 들어도, 써도.

5. Prohibition: -(으)면 안 되다

-(으)면 안 되다 "must not" is the ending -(으)면 (Chapter 5) plus 안 되다 "doesn't work": 그렇게 하면 안 돼요 "You must not do it like that", 이 차에 디젤을 넣으면 안 됩니다 "You must not put diesel in this car", 유아에게 그런 말을 하면 안 돼요 "You must not say that to a young child". A more formal "should not" is -아/어서는 안 되다: 밥을 많이 먹어서는 안 돼요 "You shouldn't eat a lot", 사람을 겉모습으로 평가해서는 안 돼요 "You shouldn't judge people by their looks".

As a question, the same phrase asks politely whether something is acceptable: 더 빨리 하면 안 돼요? "Can't you do it faster?". The short answer "No" to a permission question is 안 돼요. A related positive pattern is -(으)면 되다 "it's enough if", used for advice: 서울역에서 내리면 됩니다 "You just get off at Seoul Station".

You want to say	Pattern	Example
You may…	-아/어도 돼요	앉아도 돼요
You don't have to…	안 -아/어도 돼요	안 와도 돼요
You must…	-아/어야 해요/돼요	와야 돼요
You must not…	-(으)면 안 돼요	앉으면 안 돼요

6. Guessing: -(으)ㄹ 것 같다 and -(으)ㄴ/는 것 같다

-(으)ㄹ 것 같다 (future modifier + 것 + 같다 "seem") says that something is probably going to happen or be the case: 비가 올 것 같아요 "It looks like it will rain", 우리는 늦을 것 같아요 "We will probably be late", 문이 열려 있을 것 같아요 "The door is probably open". The subject can be anything. Other tenses use the Chapter 7 modifiers:

What you guess	Form	Example
Future / likely	-(으)ㄹ 것 같다	비가 올 것 같아요
Present, verb (observing)	-는 것 같다	엄마는 기다리고 있는 것 같아요 "Mum seems to be waiting"
Present, adjective	-(으)ㄴ 것 같다	이 집은 큰 것 같아요
Past, with evidence	-(으)ㄴ 것 같다	친구가 간 것 같아요
Past, a guess	-았/었을 것 같다	아빠가 이미 냈을 것 같아요 "Dad probably already paid"
이다	-인 것 같다	그 사람은 학생인 것 같아요

The sources checked give the future-form examples and the 이다 and "mum seems to be waiting" and "dad probably paid" examples; the table's adjective and past-with-evidence rows follow the Chapter 7 modifier table. Do not say 그렇는 것 같아요: the adjective 그렇다 loses its ㅎ, giving 그런 것 같아요 (Chapter 3).

7. "It seems that…": -나 보다 / -(으)ㄴ가 보다

Another way to say "it seems, it appears" is -나 보다 after a verb and -(으)ㄴ가 보다 after an adjective or -인가 보다 after 이다. The speaker has seen or heard evidence and infers the cause: 비가 오나 봐요 "It seems to be raining", 사람이 많은가 봐요 "There seem to be a lot of people", 학생인가 봐요 "(They) seem to be a student", 잤나 봐요 "(They) seem to have been asleep" (past -았/었나 보다). It is more observational than -(으)ㄹ 것 같다 and is not used to talk about your own feelings or plans. The sources checked do not cover this ending: it is from general knowledge.

8. Expectation and pity: -(으)ㄹ 텐데

-(으)ㄹ 텐데 is built from the pseudo-noun 터 + 이다 + -ㄴ데: always -ㄹ/을 + 터 + 이다 + ㄴ데. It says "it should be the case, and…", with a feeling of expectation, worry or "what a shame". It is a little more sure than -(으)ㄹ 것 같다:

• 비가 올 텐데 "It's probably going to rain (and so…)"
• 그가 집에 없을 텐데 "He probably isn't at home (but)…"
• 음식이 더 있으면 좋을 텐데 "It'd be good if there were more food (but there isn't)." (the author's gloss of the nuance)
• Connecting two clauses: 길이 막힐 텐데 지하철로 가요 "The roads will probably be jammed, so let's take the subway."

It is typically used when the speaker is not the one doing the action. One exception is the intention form -(으)ㄹ 테니까 (here the speaker is the subject): 지금 갈 테니까 조금 더 기다려 주세요 "I'm leaving now, so please wait a little longer". Ending a sentence with -(으)ㄹ 텐데요 leaves the thought hanging, soft and polite.

9. Worry: -(으)ㄹ까 봐

-(으)ㄹ까 봐 says "for fear that, in case": the first clause is what you are afraid of, and the second shows what you do or feel because of it. One source example, 집주인이 부서진 거울을 찾아낼까 봐 걱정돼요 "I'm worried that the landlord will find the broken mirror", appears only as a vocabulary example, so the rule is from general knowledge: vowel stem + -ㄹ까 봐, consonant stem + -을까 봐 (늦을까 봐, 잊을까 봐). Another: 비가 올까 봐 우산을 가져왔어요 "I brought an umbrella in case it rained".

🗣️ In Use — 실제 예문

📋 Quick Reference — 요약표

Meaning	Pattern	Example
can	-(으)ㄹ 수 있다	할 수 있어요
cannot	-(으)ㄹ 수 없다 · 못 · -지 못하다	할 수 없어요 · 못 해요
must	-아/어야 하다/되다	가야 돼요
need to / no need	-(으)ㄹ 필요가 있다/없다	갈 필요가 없어요
may	-아/어도 되다	가도 돼요
don't have to	안 -아/어도 되다	안 가도 돼요
must not	-(으)면 안 되다	가면 안 돼요
probably	-(으)ㄹ 것 같다	갈 것 같아요
seems	-나 / -(으)ㄴ가 보다	가나 봐요 · 큰가 봐요
should (expectation)	-(으)ㄹ 텐데	올 텐데
in case / for fear	-(으)ㄹ까 봐	늦을까 봐

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