Korean can’t

Korean grammar has 2 ways to say ‘can not’. One is a negative form of ‘할수 있다’ and another is an unique affix 못 for ‘can not’. Koreans use both. However, 할 수 없다 sounds much more formal even though you can hear it in a casual conversation.

할 수 없다

할 수 없다 is exact opposite to 할 수 있다. It literally means ‘There is no way to do something’. But it sounds quite formal.

입장 할 수 없어요
(We) can’t enter

그건 먹을 수 없어요
(You) can’t eat that

I dropped subjects on each sentence. It works like pronouns in English. It has rules but you will learn it in another course. To be honest, there is no way to know what or who is the subject in a sentence. You just have to read context.

일 수 없다

You learned 일 수 있다 is more like an assumption, not ‘can’. The negative form of 일 수 있다 is 일 수 없다. But, it’s not an assumption anymore. 일 수 없다 literally means ‘there is no way that something is something’

일 수는 없다 is more common than 일 수 없다. 일 수는 없다 is almost same to ‘it can’t be’ especially with stuffs, not person.

이게 기차 일 수는 없어요
This can not be a train

여기서 계속 서성일 수는 없어요
We can’t keep pacing here like this

있을 수 없다

있을 수 없다 is almost same to 일 수 없다. It doesn’t have a nuance of guessing. it’s ‘- can not be + location’. This one is a bit tricky because normally Koreans use it when they talk about themselves.

It doesn’t have a meaning of possession AT ALL.

여기 있을 수 없어요
(I/we) can’t be here

집에 있을 수 없어요
I can’t be home

못- prefix : Can’t

못 is an Korean prefix that means ‘can not’. It’s very similar to 안 and very often used in casual conversations. Sometimes native Koreans use ‘못-’ prefix to say ‘don’t’ especially when they say ‘I don’t want to do it’.

입장 못했어요
(I) couldn’t get in
= 하다 verb after a noun

그건 못먹어요
(You/I) can’t eat that
= 하다 verb after a root

여기 못있어요
(We/You) can’t be here
= Be location verb

‘Can’t’ As Shouldn’t

In English, you can say ‘you can not do it’ instead of ‘you should not do it’. In Korean? it’s super weird to say it. Koreans use only ‘안(don’t)’ to mean ‘shouldn’t’ because we have a lot of conjugations to ask people to do something.

이렇게 그만 두면 안되죠
You can’t quit like this
= 안 is ‘don’t’

Make It Natural

할 수 없다 and 못 can’t be used with 이다 as ‘be + noun’ and 있다 as ‘possessive’. You must use 하다 verbs for it.

음악 선생님은 일 수 없어요 (Wrong)
음악 선생님은 못 이에요 (Wrong)
음악 선생님은 될 수 없어요
음악 선생님은 못 되요
I can’t be a music teacher
= You must use verb ‘되다’ (become) instead of 이다

if you say ‘한국인 일 수 없어요’ then it would sound like ‘it can’t be possible he/she is Korean’ and it doesn’t even sound natural much. Grammatically yes, but this is not what you really can hear of in almost situations.

차 있을 수 없어요 (Wrong)
차 못있어요 (Wrong)
차 살수 없어요
차 못사요
I can’t have a car
= You must use other verbs such as 사다(buy), 갖다(get).