While/And Then Suddenly (-다가)

-다가 connects two clauses where the first action is interrupted, stopped, or switched to the second action. It attaches to the verb stem and implies that the subject was in the middle of doing something when a change occurred.

For example, 공부하다가 잠들었어요 means 'I was studying and then fell asleep.' The nuance is that studying was interrupted by falling asleep. This pattern is commonly used when describing unexpected changes or interruptions in action.

-다가 requires that both clauses share the same subject. You cannot use it when different people perform the two actions. It also implies that the first action was not completed before the switch to the second action. This is different from -고, which simply sequences completed actions.