-아/어서 is used to connect two clauses where the first clause is the reason for the second. It means "because," "so," or "since."
Structure
Clause 1 + -아/어서, Clause 2
Breakdown:
- -아/어: Connective ending (vowel harmony)
- 서: Because/so connective
Meaning: "Because [clause 1], [clause 2]" or "[Clause 1], so [clause 2]"
Vowel Harmony Rules
Bright Vowels (ㅏ, ㅗ): -아서
Last vowel is ㅏ or ㅗ:
- 가다 → 가서 (go, so/because)
- 오다 → 와서 (come, so/because)
- 보다 → 봐서 (see, so/because)
- 좋다 → 좋아서 (good, so/because)
Dark Vowels: -어서
Last vowel is NOT ㅏ or ㅗ:
- 먹다 → 먹어서 (eat, so/because)
- 서다 → 서서 (stand, so/because)
- 크다 → 커서 (big, so/because)
- 적다 → 적어서 (few, so/because)
하다 Verbs: -해서
All 하다 verbs:
- 하다 → 해서 (do, so/because)
- 공부하다 → 공부해서 (study, so/because)
- 피곤하다 → 피곤해서 (tired, so/because)
Core Usage: Expressing Reason
Because... (Reason → Result)
Pattern: [Reason]-아/어서 [Result]
Examples:
- 배고파서 먹었어요 (I was hungry, so I ate)
- 피곤해서 잤어요 (I was tired, so I slept)
- 바빠서 못 갔어요 (I was busy, so I couldn't go)
- 비가 와서 집에 있었어요 (It rained, so I stayed home)
Common Usage Patterns
Daily Reasons
Physical states:
- 아파서 병원에 갔어요 (I was sick, so I went to the hospital)
- 배고파서 밥 먹었어요 (I was hungry, so I ate)
- 피곤해서 일찍 잤어요 (I was tired, so I slept early)
- 추워서 옷을 입었어요 (It was cold, so I wore clothes)
Circumstances:
- 시간이 없어서 못 갔어요 (I had no time, so I couldn't go)
- 돈이 없어서 못 샀어요 (I had no money, so I couldn't buy it)
- 길이 막혀서 늦었어요 (Traffic was bad, so I was late)
- 비가 와서 취소했어요 (It rained, so we cancelled)
Emotional Reasons
Feelings causing actions:
- 기뻐서 웃었어요 (I was happy, so I smiled)
- 슬퍼서 울었어요 (I was sad, so I cried)
- 화나서 소리쳤어요 (I was angry, so I yelled)
- 걱정돼서 전화했어요 (I was worried, so I called)
Sequential Actions with -아/어서
Natural Sequence
First action leads to second:
- 집에 가서 쉬었어요 (I went home and rested)
- 밥을 먹어서 배불러요 (I ate, so I'm full)
- 공부해서 시험에 합격했어요 (I studied, so I passed the exam)
Note: Can mean temporal sequence OR causal relationship
With Adjectives
State Causing Result
Adjective + -아/어서:
- 좋아서 샀어요 (It was good, so I bought it)
- 예뻐서 봤어요 (It was pretty, so I looked)
- 비싸서 안 샀어요 (It was expensive, so I didn't buy it)
- 쉬워서 금방 했어요 (It was easy, so I did it quickly)
- 맛있어서 많이 먹었어요 (It was delicious, so I ate a lot)
Important Restrictions
Cannot Use with Certain Endings
❌ Cannot combine with:
- Future tense: -(으)ㄹ 거예요
- Commands: -(으)세요
- Proposals: -(으)ㅂ시다
- Suggestions: -(으)ㄹ까요?
- Requests: -아/어 주세요
❌ Wrong: 바빠서 가세요 ✅ Correct: 바빠서 가요 or 바쁘니까 가세요
Use -(으)니까 Instead
For commands/requests, use -(으)니까:
- 바쁘니까 가세요 (You're busy, so please go)
- 피곤하니까 쉬세요 (You're tired, so please rest)
Negative Forms
With 안 (Not)
Negative reason:
- 안 좋아서 못 갔어요 (It wasn't good, so I couldn't go)
- 안 바빠서 갈 수 있어요 (I'm not busy, so I can go)
- 안 추워서 괜찮아요 (It's not cold, so it's okay)
With -지 않아서
Formal negative:
- 좋지 않아서 바꿨어요 (It wasn't good, so I changed it)
- 맞지 않아서 돌려줬어요 (It didn't fit, so I returned it)
Natural Translations
Various English Equivalents
-아/어서 can be translated as:
- Because: 아파서 (because I'm sick)
- So: 바빠서 (I'm busy, so...)
- Since: 비가 와서 (since it's raining)
- As: 피곤해서 (as I'm tired)
- And then: 가서 (went and then)
Choose based on natural English
Example Dialogues
Dialogue 1: Explaining Absence
A: 어제 왜 안 왔어요?
(Why didn't you come yesterday?)
B: 아파서 못 갔어요.
(I was sick, so I couldn't go.)
Dialogue 2: Being Late
A: 왜 늦었어요?
(Why are you late?)
B: 길이 막혀서 늦었어요. 죄송합니다.
(Traffic was bad, so I'm late. I'm sorry.)
Dialogue 3: Shopping
A: 왜 안 샀어요?
(Why didn't you buy it?)
B: 비싸서 안 샀어요.
(It was expensive, so I didn't buy it.)
Dialogue 4: Plans Changed
A: 피크닉 갔어요?
(Did you go to the picnic?)
B: 아니요, 비가 와서 취소했어요.
(No, it rained so we cancelled.)
Contrast with -(으)니까
-아/어서 vs -(으)니까
-아/어서: Natural reason, softer
- 바빠서 못 갔어요 (I was busy, so I couldn't go)
- → Neutral, explaining
- → Cannot use with commands
-(으)니까: Emphasizes cause, stronger
- 바쁘니까 가세요 (You're busy, so please go)
- → Can use with commands/requests
- → More assertive
When to Use Each
Use -아/어서:
- Past tense statements
- Simple explanations
- Natural sequences
- Softer tone
Use -(으)니까:
- Commands/requests
- Stronger causation
- Discovering reasons
- More formal
Common Expressions
Apologizing with Reasons
- 늦어서 죄송합니다 (I'm sorry for being late)
- 못 와서 미안해요 (Sorry I couldn't come)
- 연락 못 해서 죄송해요 (Sorry I couldn't contact you)
Thanking with Reasons
- 도와줘서 고마워요 (Thank you for helping)
- 와 줘서 감사합니다 (Thank you for coming)
- 기다려 줘서 고마워요 (Thanks for waiting)
Explaining Situations
- 시간이 없어서요 (I don't have time)
- 돈이 부족해서요 (I don't have enough money)
- 아직 잘 몰라서요 (I don't know well yet)
Common Mistakes
❌ Incorrect: 가고 해서
Mixing connectives
✅ Correct: 가서
Simple -아/어서
❌ Incorrect: 피곤해서 쉬세요
Command after -아/어서
✅ Correct: 피곤하니까 쉬세요
Use -(으)니까 for commands
❌ Incorrect: 갔아서
Double past tense
✅ Correct: 가서
-아/어서 doesn't conjugate for tense
Multiple Reasons
Chaining Multiple -아/어서
Two or more reasons:
- 춥고 배고파서 집에 갔어요 (It was cold and I was hungry, so I went home)
- 비가 오고 바람이 불어서 취소했어요 (It rained and was windy, so we cancelled)
Pattern: Reason 1 + 고 + Reason 2 + -아/어서
Summary Table
| Reason | Result | Complete Sentence |
|---|---|---|
| 배고파서 | 먹었어요 | 배고파서 먹었어요 |
| 피곤해서 | 잤어요 | 피곤해서 잤어요 |
| 비가 와서 | 못 갔어요 | 비가 와서 못 갔어요 |
| 비싸서 | 안 샀어요 | 비싸서 안 샀어요 |
Key Takeaways
✅ Expresses reason/cause: "Because" / "So"
✅ Vowel harmony: -아서/-어서/-해서
✅ Natural explanations: Softer, more natural
✅ Cannot use with: Commands, suggestions, future
✅ For commands: Use -(으)니까 instead
✅ Very common: Essential for explaining
-아/어서 is one of the most frequently used connectives in Korean for explaining reasons and causes. It's natural, versatile, and essential for everyday communication when you need to explain why something happened or why you did something.