In the previous lesson, we learned how to use -(으)ㄹ 줄 알다 to say “to think/know that something will happen”. This sentence ending, however, can be also used to express “can”, “to be able to”, or “to know how to”. The same meanings can also be expressed through -(으)ㄹ 수 있다, so through this lesson, let’s find out how these two verb endings are used similarly or differently to express “can” or “to be able to”.

-(으)ㄹ 수 있다
This ending was introduced in Level 2 Lesson 17. This is the basic way to say “can” or “to be able to”. When the particle -도 [-do] is used after the noun 수 [su], it becomes -(으)ㄹ 수도 있다 and it means that something “could” happen or something “might be” in a certain state.

수 [su] basically means “possibility” or “method”.

Ex)
이거 할 수 있어요?
[i-geo hal su i-sseo-yo?]
= Can you do this?

언제 올 수 있어요?
[eon-je ol su i-sseo-yo?]
= When can you come?

여기에서 뭐 살 수 있어요?
[yeo-gi-e-seo mwo sal su i-sseo-yo?]
= What can I buy here?

How to say “can NOT”
You need to change 있다 [it-da] to 없다 [eop-da].

-(으)ㄹ 줄 알다
This structure was introduced in the previous lesson as a sentence ending that means “to think/know that something will happen/be in a certain state”. But when you are talking about “knowing how to do something” or “being able to do something”, 줄 [jul] here means “method” or “how”.

-(으)ㄹ 줄 = how/method
알다 = to know

-(으)ㄹ 줄 알다 = to know how to + V, to be able to + V

Ex)
운전 할 줄 알아요?
[un-jeon hal jul a-ra-yo?]
= Do you know how to drive?
= Can you drive?

김치 만들 줄 알아요?
[gim-chi man-deul jul a-ra-yo?]
= Do you know how to make kimchi?
= Can you make kimchi?

영어 할 줄 알아요?
[yeong-eo hal jul a-ra-yo?]
= Do you (know how to) speak English?
= Can you speak English?

How to say “can NOT”
You need to change 알다 [al-da] to 모르다 [mo-reu-da]. 모르다 means “to not know”.

Difference between -(으)ㄹ 수 있다 and -(으)ㄹ 줄 알다
-(으)ㄹ 수 있다 is the basic way to say “can” or “to be able to”, so it usually refers to one’s actual “capability” of doing something. And on the other hand, -(으)ㄹ 줄 알다 means that you know how to do something, and you can do it, but in most cases, you have LEARNED how to do it. Therefore there can some things that you CAN (-을 수 있다) do (potentially), but CAN’T do it yet because you still don’t know how to do it.

Ex)
아직 할 줄 몰라요. 그런데 할 수 있어요.
[a-jik hal jul mol-la-yo. geu-reon-de hal su i-sseo-yo.]
= I don’t know how to do it yet. (I can’t do it yet.) But I can do it.    

More Sample Sentences
1. 이거 할 줄 알아요?
[i-geo hal jul a-ra-yo?]
= Do you know how to do this?

2. 저는 영어 할 줄 몰라요.
[jeo-neun yeong-eo hal jul mol-la-yo.]
= I don’t speak English.
= I don’t know how to speak English.
= I can’t speak English.

3. 그거 한국어로 말할 수 있어요?
[geu-geo han-gu-geo-ro mal-hal su i-sseo-yo?]
= Can you say that in Korean?

그거 한국어로 말할 줄 알아요?
= Do you know how to say that in Korean?

4. 자전거 탈 줄 알아요?
[ja-jeon-geo tal jul a-ra-yo?]
= Do you know how to ride a bike?
= Can you ride a bike?

자전거 탈 수 있어요?
[ja-jeon-geo tal su i-sseo-yo?]
= Can you ride a bike?
= Can you ride a bike (now/like that)?

How to tell which meaning -(으)ㄹ 줄 알다 takes
-(으)ㄹ 줄 알다 can mean either “to know how to” and “to know/think that something will happen”. There is no certain rule for this, but you can usually figure out by context.

Examples
제가 올 줄 알았어요?
[je-ga ol jul a-ra-sseo-yo?]

In the example above, if you interpret it as “Did I know how to come here?”, it is a bit weird. So you know it SHOULD mean “Did you know I would come here?” or “Did you think I would come here?”

이거 만들 줄 알아요?
[i-geo man-deul jul a-ra-yo?]

In the example above, if you interpret it as “Do you think …” or “Do you know …”, you don’t have enough information to figure out who’s going to make “this” and this meaning is usually not commonly used in the present tense, so you know it’s easier to understand it as a question, asking “Do you know how to make this?”