📝 Grammar B1

-아서/어서

-aseo/eoseo

Because / and then (cause/sequence)

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What it means

Two main uses: (1) expressing reason/cause (because), and (2) expressing a sequence of actions (and then). -아서 after bright vowels (ㅏ, ㅗ); -어서 after others.

Nuance & when to use

Key constraint: -아서/어서 cannot combine with past tense markers. 피곤했어서 is wrong; use 피곤해서. Tense is only expressed in the final clause. Both clause subjects are usually the same.

⚠ Common mistake

Adding tense to the -아서/어서 clause: 피곤했어서 (wrong) → 피곤해서 (correct). The -아서/어서 clause stays in base form; tense goes in the result clause only.

Example sentences

배가 고파서 밥을 먹었어요. Baega gopaseo babeul meogeosseoyo. I was hungry, so I ate.
비가 와서 우산을 가져갔어요. Biga waseo usaneul gajyeogasseoyo. It rained, so I took an umbrella.
손을 씻고 밥을 먹어서 건강해요. Soneul ssitgo babeul meogeoseo geonganghaeyo. I wash my hands and then eat, so I stay healthy.
늦게 자서 아침에 피곤해요. Neutge jaseo achime pigonhaeyo. I slept late, so I'm tired in the morning.

See also

-기 때문에 -(으)니까 -지만 접속사
References Naver Korean Dictionary ↗ 국립국어원 표준국어대사전 ↗
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More B1 lessons

-겠어요 -gesseoyo I will / I think / Seems like (intention/inference) 열정 yeojeong passion / enthusiasm -(으)ㄹ 것이다 -(eu)l geosida Will / Going to (future tense)
← -아/어야 하다 -지만 →

FAQ

When is this used?

Key constraint: -아서/어서 cannot combine with past tense markers. 피곤했어서 is wrong; use 피곤해서. Tense is only expressed in the final clause. Both clause subjects are usually the same.

What's a common mistake?

Adding tense to the -아서/어서 clause: 피곤했어서 (wrong) → 피곤해서 (correct). The -아서/어서 clause stays in base form; tense goes in the result clause only.

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