The connective expression (으)ㄴ데 / 는데

Summary of usage:

1) -provide background information

2) -express contrastive meanings(=지만)

3) -justify a request or proposal

4) -avoid a direct rejection (-being polite)

Conjugation forms:

Adjectives---(으)ㄴ데

Copula 이다/아니다---(으)ㄴ데

Verb---는데

Past tense (any type of)---는데

Existential 있/없---는데

Usage 1) -provide background information

한국어 책을 사고 싶은데, 어디에서 팔아요? I want to buy a Korean book, where should I go?

어제 예약을 했는데요. I made a reservation yesterday.

늦었는데, 일찍 주무세요. It's late, please go to bed early.

그 옷은 가격이 비싼데, 제가 어떻게 사겠어요? They are expensive, how could I buy them?

Usage 2) -express contrastive meanings(=지만)

어제는 따뜻했는데, 오늘은 추워요. It was warm yesterday, but it is cold today.

김치는 맛이 있는데, 좀 짜요. Kimchi tastes good, but it's salty.

그 학교는 집에서 먼데, 버스는 많이 있어요. The school is far, but buses are available.

커피를 사고 싶었지만, 다 떨어졌더군요. I wanted to buy coffee, but it ran out.

Usage 3) -justify a request or proposal

점심 시간인데, 식당에서 먹을까요? It's lunchtime, shall we eat at the restaurant?

내용이 좀 어려운데, 다시 한번 말씀에 주세요. It was difficult. So, please explain it again to me.

시간이 없는데, 내일 해도 돼요? I don't have time now, can I do it tomorrow?

날씨가 더운데 시원한 물이라도 한잔 드세요. It’s hot. Would you like to drink cold water?

Usage 4) -avoid a direct rejection (-being polite / indirect)

A: 같이 커피한잔 해요 Let's have coffee together

B: 지금 가야 하는데요. I have to go now. (Sorry.)

A: 내일 3명으로 테이블 예약을 부탁해요. Please reserve a table for three tomorrow.

B: 내일은 만석인데요. It's fully reserved tomorrow. (I am sorry.)

잘 모르겠는데요. I'm not sure. (Sorry.)