Some of my students were confused using “If/(으)면” and “when/(을)ㄹ 때” because they can be used in the similar situation. For instance, when you go to the store, please buy me a coke. If you go the store, please buy me a coke. Can you classify what is different between two sentences? We all know that they are different, but it is not easy to explain them. Here is easy explanation “If” is using in hypothetical situations. I am not sure a person goes to the store or not but if the person goes the store, I want to get a coke from the person. However, when you use “When”, it is talking the time. Let’s read more examples below to get ideas.

If you are full, please stop eating/ 배가 부르면 그만 드세요/bae ga bu reu myun gu man due sae yo.

When you are full, please stop eating/ 배가 부를 때 그만 드세요/ bae ga bu reul ddae gu man due sae yo.

Can you tell the hypothetical situation in the first sentence? I am sure you can. Above the examples are that you can use “If” and “When” at the same time with different meaning. However the example below is not.

미국에 가면 요리를 많이 할 거예요/ If I go to America, I will cook a lot.

미국에 갈 때 요리를 많이 할 거예요/ When (While, at the time) I go to America, I will cook a lot.

The first one is fine because it is in hypothetical situation, but the second one sounds silly because “When” is time (the time when). Please watch the video below to see more examples.