Sometimes in Korean you want to talk about why something happened or is how it is—that is, reasons. There are a few ways to do this. Let’s look at two of the most common ways to express reasons: -아/어서 ([이]라서) and -(으)니까.
This one is pretty basic and used often. You can use this to make the antecedent clause (the first clause of the sentence) the reason for the following clause. One thing to remember is that you can’t use this form to express reasons with commands and suggestions.
- 우리 집에서 정말 멀어서 가기는 좀 귀찮아요. (Because it’s very far from my house, going [there] is a bit annoying.)
- 날씨가 좋아서 기분이 좋아요. (Because the weather is nice, I’m in a good mood.)
If you use this with 이다 or 아니다, you can use -(이)라서 instead of -아/어서.
- 그분은 선생님이라서 이 문제를 풀 수 있어요. (Because that person is a teacher, they can solve this problem.)
- 제 것이 아니라서 만지지 않은 게 나아요. (Because it’s not mine, not touching it is better.)
Even if you want to express something that happened in the past as your reason, you should not conjugate the verb to the past tense before adding 아/어서.
- 늦게 와서 미안해요. (Sorry for being late [LIT: Because I came late, I am sorry].)
- 어젯밤 아주 늦게 자서 오늘 정말 피곤해요. (Because I slept late last night, I am really tired today.)
This form is similar to the previous form, but you can use it with commands and suggestions! You can also use past tense before this form.
- 큰 케이크를 준비해 왔으니까 케이크를 가져오지 마세요. (Because I prepared and brought a big cake, please don’t bring a cake.)
- 이 숙제는 어려우니까 좀 이따 친구에게 도움을 부탁할 거예요. (Because this homework is hard, in a little while I will ask my friend for help.)
- 아기가 잠을 자고 있으니까 드럼을 치지 마세요. (Because the baby is sleeping, please don’t play the drum.)
BONUS GRAMMAR: -(으)ㄴ/는지
This form is a bit more complicated and not quite as common as the previous two, but I like it a lot! This is used when you want to suggest a possible reason for something, but you aren’t totally sure that it really is the reason.
When you use this form with present tense descriptive verbs (adjectives), use -ㄴ지 if it ends with a vowel and -은지 if it ends with a consonant.
- 미나 씨는 너무 바쁜지 요즘 전화를 자주 안 해요. (Maybe because Mina’s too busy, she doesn’t call often lately.)
- 이 옷이 너무 작은지 좀 불편해요. (Maybe because these clothes are too small, they’re a bit uncomfortable.)
When you use this form with present tense action verbs or past tense action and descriptive verbs, use -는지.
- 민호 씨는 돈을 많이 버는지 정말 인기가 좋아요. (Maybe because Minho earns a lot of money, he’s really popular.)
- 점심을 빨리 먹었는지 배탈이 났어요. (Maybe because I ate lunch quickly, I have a stomachache.)
- 그 핸드폰이 너무 비쌌는지 한나 씨는 이 걸로 사게 됐어요. (Maybe because that cell phone was too expensive, Hanna ended up buying this one.)