[Korean grammar] -을지도 모르다/ ㄹ지 모르다 Expressing Conjecture and Supposition

가: 여보, 우산 가지고 가세요.
Honey, take an umbrella with you.
나: 날씨가 맑온데요, But the weather’s fine.
가: 장마철이잖아요. 장마철에는 갑자기 비가 올지도 몰라요.
It’s the rainy season. In the rainy season, it might start raining suddenly.

가: 마크 씨가 얼마 전에 산 책을 다 읽있겠지요? 제가 좀 빌려서 읽으려고요.
Don’t you think Mark has finished reading that book he bought recently?
나: 요즘 일이 많아서 다 못 읽었을지도 몰라요.
There’s so much to do these days that he may not have finished reading it yet.

-을지도 모르다/ ㄹ지 모르다 is used to indicate the speaker’s view that something might happen or could possibly. The form -(으)ㄹ지 모르다 is also used.

가: 사토 씨가 어디 있는지 혹시 아세요?
Do you happen to know where Sato is?
나: 사토 씨는 보통 집에 일찍 가지만 내일 시험이 있으니까 도서관에 있을지도 몰라요.
Sato normally goes home early, but he’s got a test tomorrow, so he might be in the library.

가: 휴지랑 비누를 다 썼네요. 내일 마트에 갔다 와야겠어요.
We’re all out of toilet paper and soap. It looks like we’ll have to go to the mart tomorrow
나: 내일부터 추석 연휴라서 문을 안 열지도 몰라요. 오늘 갔다 오는 게 좋을 것 같아요. Tomorrow’s the first day of the Chuseok holiday, so it might be closed. I think we should go today.

가: 제가 수진 씨를 불렀는데 대답을 안 하더라고요. 저한테 화가 났을까요?
I tried to get Sujin’s attention, but she didn’t answer. Do you think she’s mad at me?
나: 친구들이랑 이야기하느라고 못 들었을지 몰라요. 너무 신경 쓰지 마세요.
She likely didn’t hear you because she was busy talking with her friends. Don’t get too worked up about it.

1. Because this expression indicates something that is possible, but unlikely, to happen, it can come across as rude to a person who is worried about an event that is important to him or her.
가: 이번 시험에 꼭 합격해야 할 텐데요.
I’ve really got to pass this exam.
나: 열심히 공부했으니까 합격할지도 몰라요.
You’ve studied really hard, so maybe you’ll pass.
가: 뭐라고요? 제가 떨어질 가능성이 더 많다는 얘기예요?
What? Are you saying it’s more likely that I’ll fail?

The phrase 합격할지도 몰라요 means that the speaker thinks the hearer might pass even though the chances of doing so are slim. Naturally, the hearer would feel bad upon hearing such a statement. In this case, therefore, it is better to use the phrase 합격할 거예요，which expresses the speaker’s belief that there is a very high probability that the hearer will pass.

2. The past tense form of this expression is -았/었을지도 몰라요. It is incorrect to change 몰라요 to 몰랐어요,
– 게이코 씨가 파티에 간다고 했지만 안 갔을지도 몰랐어요. (X)
->게이코 씨가 파티에 간다고 했지만 안 갔을지도 몰라요. (O)