-아/어서 (Reason) vs -(으)니까
Compare Korean reason endings -아/어서 and -(으)니까: nuance, politeness, and when each sounds natural.
Quick takeaway
-아/어서 is the everyday cause/result connector. -(으)니까 feels more like you’re justifying or informing — and it works better before commands and suggestions.
-아/어서 (Reason)
Because / So
Used to express the reason or cause for the action/state in the following clause. It connects a reason with a result.
When to use it
Neutral cause → result in statements: “I was tired, so I went home.”
Examples
-
배가 아파서 병원에 갔어요.
I had a stomachache, so I went to the hospital.
-
늦어서 죄송합니다.
I'm sorry for being late.
-
날씨가 더워서 아이스크림을 먹었어요.
Because the weather was hot, I ate ice cream.
-(으)니까
Because / Since
Used to provide a subjective reason or justification for an action, suggestion, or command.
When to use it
Giving a reason before advice, requests, or stronger justifications: “It’s late, so let’s go.”
Examples
-
날씨가 추우니까 따뜻하게 입으세요.
Since the weather is cold, please dress warmly.
-
제가 도와줄 테니까 걱정하지 마세요.
Since I will help you, please don't worry.
-
시간이 없으니까 택시를 탑시다.
We don't have time, so let's take a taxi.