While (-(으)면서)

-(으)면서 connects two actions that happen at the same time by the same person. Use -면서 after vowel-ending stems and -으면서 after consonant-ending stems. 음악을 들으면서 공부해요 means 'I study while listening to music'.

Both actions in a -(으)면서 sentence must have the same subject. You cannot say *비가 오면서 나는 갔어요 (While it rained, I went), because the subjects are different. For different subjects, use other patterns like -(으)ㄹ 때 or -는 동안.

-(으)면서 can also express contrast or contradiction: 알면서 모르는 척해요 (Even though you know, you pretend not to). In this usage, it implies doing two contradictory things simultaneously. This secondary meaning is important for intermediate-level comprehension.