Korean grammar can be a daunting challenge given the tremendous amount of highly similar grammar expressions out there. Two Korean grammar forms can share the same English translation, though in Korean there are two expressions you cannot use interchangeably. This can be confounding and regretfully a lot of Korean textbooks tend to gloss over this difficult aspect of learning Korean. So, to help resolve this let’s take a look into highly similar Korean grammar expressions and explain how exactly they differ and when you can use them interchangeably. The first expressions we’ll compare are the Korean time expressions 동안, -(으)면서 and -(으)ㄹ 때.
-(으)면서 And 동안
Let’s first go over the easier part of this article: -(으)면서 And 동안. These two Korean time expressions are more or less identical and you can use them interchangeably. However, there is a very important caveat to that.
While it is true they carry the same meaning, there is a very important limitation to the verb ending -(으)면서, which 동안 does not have. Sentences that utilize -(으)면서, need to have the same subject in both clauses, meaning the subject does two actions at the same time. You cannot use the verb ending to express that something is happening while the subject of the first clause is doing something. If you want to express that, you will have to use 동안. Keep this important distinction between -(으)면서 and 동안 in mind.
-(으)ㄹ 때 Confusion
The real cause of confusion is the Korean time expression -(으)ㄹ 때. Due to its translation, many assume at first that this time expression is near identical to 동안/-(으)면서. However, this is not the case. While all these grammar forms express actions and/or events that happen simultaneously and/or their duration, -(으)ㄹ 때 expresses it to a narrower degree which is the important difference preventing you from substituting -(으)ㄹ 때 with 동안 or -(으)면서.
The key aspect of -(으)ㄹ 때 that sets itself apart from those two other expressions is its narrower time frame. When you express something with -(으)ㄹ 때, you set a very clear time boundary for when an event or action takes place. The action or event in the second clause does not occur before the event/action in the first clause or after it. This clear time boundary is what sets itself apart from -(으)면서 and 동안 which do not have this restrictive time boundary. This is important because the meaning of a sentence can have a very different meaning when you use either -(으)ㄹ 때 or 동안 for example. Let’s take a look at an example and see how the meaning changes depending on which grammar form you use.
1) 식사 때 민수 씨와 얘기했어요. (I talked to Minsu during the meal.)
2) 식사 동안 민수 씨와 얘기했어요. (I talked to Minsu during the meal.)
At first glance, both sentences offer exactly the same information, but there is a difference in the detail. In the first sentence, you are informed that the speaker only talked with Minsu during the meal. The conversation did not start before the meal and it did not continue after the meal. Only for the duration of the meal did he talk with Minsu. In the second sentence, however, this is not told. It is possible the speaker was already talking to Minsu before the meal and simply continued their conversation. It is also not possible to rule out that the conversation continued after the meal. These differences in nuances sets -(으)ㄹ 때 apart from 동안 and -(으)면서. (PS. The second sentence is far more natural than the first one given the situation)