-(으)ㄴ/ㄹ 줄 알다

-(으)ㄴ/ㄹ 줄 알다 

-(으)ㄴ 줄 알다  = to know/think that someone has done something

-(으)ㄹ 줄 알다 = to know/think that someone will do something

Let us look at some examples first.

비가 올 줄 알았어요.

I knew it was going to rain.

I thought it was going to rain.

사람이 많을 줄 알았어요.

I knew there would be a lot of people.

I thought there would be a lot of people.

How to tell whether it means "I knew" or "I thought"?

The meanings can be very different between "I knew you would like it" and "I thought you would like it". The written form for both of these in korean is the same, but the intonation in spoken korean is different. When you have more stress on the verb "알다", it means "I knew" and when the stress is on the -(으)ㄴ/ㄹ 줄 part, it means "I thought".

Ex)

어디로 갈 줄 알았어요?

(with emphasis on 알았어요) = Did you know where he would go?

(with emphasis on 어디로) = Where did you think he would go?

Different between -(ㅇ)ㄴ 줄 알다 and -(으)ㄹ 줄 알다  

Basically -(으)ㄴ 줄 알다 expresses your knowledge or assumption about a PAST ACTION or a PRESENT STATE, whereas -(으)ㄹ 줄 알다 expresses your knowledge or assumption about a FUTURE action or state.

To express your knowledge or assumption about a PRESENT ACTION, you need to use -는 줄 알다.

예쁜 줄 알다

(with emphasis on 알다) to know that something/someone is pretty

(with emphasis on 예쁜 줄) to think that something/someone is pretty

Ex)

제 친구는 자기가 세상에서 제일 예쁜 줄 알아요.

My friend thinks that she is the prettiest in the world.

간 줄 알다

(with emphasis on 알다) to know someone has gone somewhere

(with emphasis on 간 줄) to think that someone has gone somewhere

Ex)

제가 학교 간 줄 알았어요? Did you know that I had gone to school?

(with emphasis on 알았어요)

제가 학교에 간 줄 알았어요? Did you think that I had gone to school?

(with emphasis on 간 줄)

How to say "I didn't know I would..." and "I didn't think I would..."

For making the -(으) 줄 알았어요 a negative sentence, there are two ways.

One is to change 알았어요 to 몰랐어요. The other is to add "안" to the original.

Ex)

오늘 눈이 올 줄 알았어요.

I knew it would snow today.

I thought it would snow today.

오늘 눈이 올 줄 몰랐어요.

I didn't know it would snow today.

오늘 눈이 올 줄 안 알았어요.

I thought it would not snow today.

Sample sentences

1. 이게 여기 있을 줄 몰랐어요.

I didn't know it would be here.

2. 저는 효진 씨도 올 줄 알았어요.

I thought Hyojin would come too.

3. 이렇게 비싼 줄 몰랐어요.

I didn't know it was this expensive.

4. 저는 안 어려울 줄 알았어요.

I thought it would not be difficult.

5. 제가 뭐라고 말할 줄 알았어요?

What do you think I would say?