-(으)ㄹ 텐데 — Would, suppose, must be

This expression is a combination of -(으)ㄹ 터아다，which expresses a particular future situation or intention to do something, and (으)ㄴ/는데, which expresses the background situation or state of affairs related to what is to follow in the sentence.

As such, it is used to express an expected or intended future state of affairs.

In the first clause of the sentence, a strong intention or expectation about a future event or situation is given, and in the second clause (following -(으)ㄹ 텐데) a statement either related or contrary to the first clause is given.

Details

This expression can also be used at the end of a sentence in the form -(으)ㄹ 텐데요 but, in this case, it can also express the speaker's supposition or assumption about the situation being discussed.

가: 제나 씨에게 같이 여행 가자고 할까요?

Shall we ask Jena to go on the trip with us?

나: 제나 씨는 요즘 바쁠 텐데요.

I think Jena is busy these days.

가: 경수 씨가 요즘 시험 준비하느라 바쁘대요.

I heard Gyeongsu is busy trying to prepare for his exam.

나: 이번에는 꼭 합격해야 할 텐데요.

He really has to pass this time.

가: 태풍이 와서 비행기가 모두 취소되었어요.

All the flights were canceled because of the typhoon.

나: 태풍이 오지 않았더라면 비행기가 취소되지 않았을 텐데요.

They wouldn't have been canceled if there hadn't been a typhoon.

The differences between -(으)ㄴ/는데 and -(으)ㄹ 텐데 are summarized below.

Kimchi Reader

Used to express an expected or intended future event.