-(으)니까
because, since — the speaker’s reasoning
The other “because.” Where -아서/어서 states a plain cause, this one presents the reason as your grounds for what follows — which is why only this ending can lead into a request.
Build it
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When to use it
Two things make -(으)니까 different from -아서. It accepts commands and suggestions: 추우니까 창문을 닫으세요. And it takes tense: 어제 갔으니까 오늘은 안 가요. Both are impossible with -아서.
Attachment follows the standard rule — vowel stems take 니까, consonant stems 으니까 — with the usual ㄹ behaviour: the ㄹ drops. 만들다 gives 만드니까, 살다 gives 사니까.
It has a second use worth knowing: discovery. Attached to an action, it can mean “upon doing X, I found that Y”: 집에 가니까 아무도 없었어요. Here it is not giving a reason at all, just a sequence in which something was noticed.
How to attach it
| Stem type | Form | Example |
|---|---|---|
| Ends in a vowel | -니까 | 가다 → 가니까 |
| Ends in a consonant | -으니까 | 먹다 → 먹으니까 |
| Ends in ㄹ | ㄹ drops | 만들다 → 만드니까 |
| Past | -았/었으니까 | 가다 → 갔으니까 |
| 이다 | -(이)니까 | 학생이니까 |
| Followed by | commands, suggestions | 닫으세요, 갑시다, 하지 마세요 |
In use
추우니까 창문을 닫으세요.
It’s cold, so please close the window.
시간이 없으니까 택시를 탑시다.
We don’t have time, so let’s take a taxi.
어제 갔으니까 오늘은 안 갈게요.
I went yesterday, so I won’t go today.
제가 만드니까 좀 기다려 주세요.
I’m making it, so please wait a moment.
집에 가니까 아무도 없었어요.
When I got home, there was nobody there.
위험하니까 조심하세요.
It’s dangerous, so be careful.
Compared with
-아서/어서
The clearest test is what comes next. If the second clause tells someone to do something, only -(으)니까 works. For a plain report of cause, either is fine, though -아서 sounds more neutral.
추워서 닫았어요. (I closed it) / 추우니까 닫으세요. (please close it)
Fixed greetings
Social formulas are locked to -아서. Substituting -(으)니까 sounds argumentative, as though you were justifying yourself.
만나서 반갑습니다. / not 만나니까 반갑습니다
-(으)ㄴ/는데
-는데 sets up background without claiming causation. Use it when you are leading into something rather than explaining it.
추우니까 닫으세요. (because it’s cold) / 추운데 창문이 열려 있어요. (it’s cold, and the window is open)
Watch out
제가 만들으니까 기다려 주세요.
제가 만드니까 기다려 주세요.
Stems ending in ㄹ drop it before this ending. The same applies to 사니까, 아니까, 노니까.
만나니까 반갑습니다.
만나서 반갑습니다.
Greetings and apologies are fixed expressions built on -아서. 늦어서 죄송합니다 works the same way.
배가 고파서 밥 먹을까요?
배가 고프니까 밥 먹을까요?
A suggestion counts as a command form, so -아서 is blocked. Any clause ending in -(으)ㄹ까요, -(으)세요, or -(으)ㅂ시다 needs -(으)니까 in front of it.
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