-아/어서
Because of, Therefore
-아/어서 connects two clauses to mean 'because' or 'and then'.
How It Works
-아/어서 is one of the most common ways to connect clauses in Korean. Its meaning depends on the context. Conjugation Rules: It attaches to the verb or adjective stem.
- If the last vowel of the stem is ㅏ or ㅗ, add -아서.
e.g., 가다 (to go) → 가서
e.g., 좋다 (to be good) → 좋아서 - If the last vowel is anything else, add -어서.
e.g., 먹다 (to eat) → 먹어서
e.g., 만들다 (to make) → 만들어서 - For 하다 verbs, it becomes 해서.
e.g., 공부하다 (to study) → 공부해서 - For the copula 이다 (to be), it becomes (이)라서 after a noun.
e.g., 학생이다 → 학생이라서 (vowel ending noun: 의사라서)
Usage 1: Cause and Effect ('because')
This is the most common usage. The first clause is the reason for the result in the second clause.
e.g., 배가 아파서 병원에 갔어요. (Because my stomach hurt, I went to the hospital.)
Important Restrictions for 'Because':
When used for a reason, the clause ending in -아/어서 has two key rules:
- No Past Tense: You cannot use the past tense marker -았/었- before -아/어서. The tense of the entire sentence is determined by the final verb.
e.g., 어제 피곤해서 일찍 잤어요. (Because I was tired yesterday, I slept early.) - Correct
e.g., 어제 피곤했어서 일찍 잤어요. - Incorrect - No Commands/Suggestions: The final clause cannot be a command (e.g., -으세요) or a suggestion (e.g., -ㅂ시다, -ㄹ까요?). For these, you must use -(으)니까.
e.g., 날씨가 좋으니까 공원에 갑시다. (Because the weather is good, let's go to the park.) - Correct
e.g., 날씨가 좋아서 공원에 갑시다. - Incorrect
Usage 2: Sequential Actions ('and then')
This usage connects two actions that are closely related and happen in order. The first action must be completed for the second one to occur.
e.g., 도서관에 가서 공부했어요. (I went to the library and then studied.)
This implies that the studying happened at the library. The two actions are linked by location. This is different from -고, which just lists actions in chronological order without implying a strong connection.
Examples (5)
- 비가 와서 길이 미끄러워요.
Because it's raining, the road is slippery.
Word by Word: Rain comes so road is slippery.
This shows a clear cause (rain) and effect (slippery road).
- 너무 피곤해서 일찍 잤어요.
I was so tired, so I went to bed early.
Word by Word: Too tired so early slept.
The reason for sleeping early was being tired. Note that '피곤해서' is used, not '피곤했어서', even though the event is in the past.
- 친구를 만나서 같이 점심을 먹었어요.
I met my friend and then we had lunch together.
Word by Word: Friend meet and then together lunch ate.
This shows a sequence of related actions. First, I met my friend, and as a direct consequence, we ate lunch.
- 서울역에 가서 기차를 탈 거예요.
I will go to Seoul Station and then take the train.
Word by Word: Seoul station to go and then train will ride.
The action of going to the station is a necessary first step for the second action, taking the train.
- 주말이라서 백화점에 사람이 많아요.
Because it's the weekend, there are a lot of people at the department store.
Word by Word: Weekend because department store at people are many.
This example uses -이라서, the form of -아/어서 for the noun + 이다 combination.
Common Mistakes
Using past tense before -아/어서.
Not Quite어제 돈이 없었어서 영화를 못 봤어요.Better어제 돈이 없어서 영화를 못 봤어요.The tense of the reason clause is implied by the final verb of the sentence. You should not add the past tense marker -았/었- to the verb stem before -아/어서.
Using -아/어서 to give a reason for a command or suggestion.
Not Quite날씨가 좋아서 산책할까요?Better날씨가 좋으니까 산책할까요?When the main clause is a command (e.g., -으세요) or a suggestion (e.g., -ㄹ까요?, -ㅂ시다), you must use -(으)니까 to state the reason, not -아/어서.
Learn This First
To express 'because/therefore', you need to understand verb conjugation.
Related Patterns
- -(으)니까So, Because
Both mean 'because', but -(으)니까 is used when the following clause is a command or suggestion. -아/어서 cannot be used in this way. -(으)니까 can also express a reason the speaker just realized.
- -고And, And Then
Both can mean 'and then' to connect sequential actions. However, -고 simply lists actions in order, while -아/어서 implies a stronger, more direct connection between the first and second action.
- -기 때문에Because
This also means 'because' and is often stronger or more formal than -아/어서. Like -아/어서, -기 때문에 is normally not used with commands or suggestions; use -(으)니까 for those. Unlike -아/어서, the reason clause can be in the past tense (e.g., 했기 때문에).
- -(으)러 가다/오다Go/come to Do
While -아/어서 can show a sequence like 'go and do something' (가서 ...하다), -(으)러 가다/오다 specifically expresses the purpose for going/coming. '밥을 먹으러 식당에 가요' (I go to the restaurant in order to eat).
Learn Next
Patterns that build on this one.