Grammar
-아서/어서
Meaning
Beginner-aseo/eoseo
Attaches to a verb or adjective stem to connect two clauses. It has two common uses: (1) the first clause is the reason or cause for the second ('because A, B'), and (2) with action verbs sharing the same subject, the first action happens and then the second follows from it in close sequence ('do A, and then B').
Form
Vowel harmony decides the shape: stem's last vowel is ㅏ or ㅗ → -아서; any other vowel → -어서; 하다 verbs → 해서. Examples: 받다 → 받아서, 먹다 → 먹어서, 공부하다 → 공부해서. A past-tense marker (-았/었-) never attaches before -아서/어서 — the connector itself already carries the time relationship. Also cannot be followed directly by a command or a 'let's' suggestion in the reason-use.
Examples
고향에 가서 성묘를 합니다.
I go to my hometown and visit the ancestral graves.
도시락을 사서 편의점 안에서 먹습니다.
I buy a lunch box and eat it inside the convenience store.
노래방이 있어서 친구와 즐겁게 놉니다.
Since there's a karaoke room, I have fun with friends.
길이 막혀서 약속에 늦었어요.
The road was jammed, so I was late to the appointment.
Common mistakes & nuance
A common beginner error is attaching the past tense before -아서/어서 (e.g. writing 먹었어서 instead of 먹어서) — the clause after -아서/어서 carries the tense for the whole sentence instead. Also, don't confuse the reason-use with -(으)니까: -아서/어서 sounds more like a natural, matter-of-fact connection, while -(으)니까 is used more for a reason the speaker wants to point out (and is required before commands/suggestions, which -아서/어서 avoids).
Similar grammar
- 때문에
때문에 attaches after a noun or a clause + 기 to state a reason more formally and starkly, and cannot express the sequential 'do A then B' meaning that -아서/어서 can — 때문에 is reason-only.
- 그래서
그래서 is a sentence-initial connector that joins two separate sentences ('...다. 그래서 ...'), while -아서/어서 fuses the two clauses into a single sentence.
- -고
-고 simply lists or sequences two actions or facts without implying that one caused or enabled the other, and it allows a past-tense marker before it; -아서/어서 implies the second action depends on the first and cannot take a past-tense marker before it.