-던(past)

V/Adj/이다,아니다 + 던

makes a verb and an adjective into a noun modifier. It can be used to recall a past situation or to indicate that the situation was interrupted before it was completed.

• To express a completed action when recalling the past, you can use 았던/었던.

-던	-었던/았던	-은
In the middle of doing something, but stopped. 내가 먹던 사과 어디에 있어요?	An action that is completely finished. 제가 먹었던 사과가 정말 맛있었어요.	An action that is completely finished. 제가 먹은 사과가 정말 맛있었어요.
completed regularly, habits.(recalling) 내가 학생 때 가던 식당이야.	completed in once, twice.(recalling) 내가 학생 때 갔던 식당이야.	Simply past tense. 내가 학생 땐 간 식당이야.
먹던 사람 → A recalling feeling while the person’s eating action was in progress at that moment 아까 케이크 먹던 사람 너무 귀여웠어.	먹었던 사람 → A recalling feeling with the nuance that I saw the person finish the eating action 아까 케이크 먹었던 사람 너무 귀여웠어.	먹은 사람 → A simple factual statement about a completed action (without the feeling of describing the situation) 벌써 밥 먹은 사람 있어?

• Since adjectives inherently express states, the difference in meaning between -던 and -았던/-었던 is ambiguous and unclear.
힘들던 하루가 끝이 났다. O
힘들었던 하루가 끝이 났다. O
 

• Like other noun modifiers we learned before, you can also use it by attaching -것.

1. 재밌게 보던