-(으)니까
-(으)니까: The 'Because' You Use Before a Command
Because / since — gives the listener your reason for what you are about to say.
How to form it
| When | Form | Example |
|---|---|---|
| Stem ends in a vowel | -니까 | 가다 → 가니까 / 오다 → 오니까 |
| Stem ends in a consonant | -으니까 | 먹다 → 먹으니까 / 좋다 → 좋으니까 |
| Stem ends in ㄹ | -니까 (ㄹ drops) | 살다 → 사니까 |
| Past tense | -았/었으니까 | 바빴으니까 / 먹었으니까 |
Where -아서 / -어서 reports a cause as plain fact, -(으)니까 hands your listener a reason. It is addressed to someone. That is the whole difference, and everything below falls out of it.
It is the only option before a command
위험하니까 조심하세요. ✅ It's dangerous, so be careful.
위험해서 조심하세요. ❌ ungrammaticalCommands, requests and suggestions are all aimed at a listener, so they need the connector that points at one.
- 피곤하니까 일찍 자세요 — You look tired, so go to bed early. (command)
- 시간 없으니까 택시 탈까요? — We’re out of time, shall we take a taxi? (suggestion)
- 바쁘니까 나중에 얘기해요 — I’m busy, let’s talk later. (request)
Check the second half. If it ends in -세요, -ㄹ까요, -읍시다, -지 마세요 or any other form aimed at the listener, you need -(으)니까. For a soft refusal that trails off without commanding, speakers often set background with -는데요 instead of spelling a full reason.
It takes past tense freely
This is the mirror image of the -아서 rule:
- 어제 바빴으니까 오늘은 쉬세요. — You were busy yesterday, so rest today.
- 밥 먹었으니까 이제 나가자. — We’ve eaten, so let’s head out now.
Both are perfectly natural. The equivalent with -아서 would be ungrammatical.
It can stand alone
When someone asks 왜요?, both connectors can carry a short answer:
A: 왜 안 왔어요? — Why didn’t you come?
B: 바빠서요. — Because I was busy. (natural)
B: 바빴으니까요. — Because I was busy. (also fine — and this one can mark the past)
Adding 요 keeps either polite. The difference is tense: -아서요 cannot take 았/었, so it stays 바빠서요. -(으)니까 takes past freely — 바빴으니까요.
A warning: a bare 니까 answer can sound clipped, even a little defensive, depending on tone. If you are explaining yourself to someone senior, a fuller sentence is safer.
Where it goes wrong
Apologies. 늦으니까 죄송합니다 is the classic learner error. It reads as “since I’m late, I guess I’m sorry” — you sound like you are defending yourself. Apologies and thanks always take -아서 / -어서:
늦어서 죄송합니다. ✅
도와주셔서 감사합니다. ✅
ㄹ-final stems. The ㄹ disappears: 살다 → 사니까, 알다 → 아니까, 멀다 → 머니까. Writing 살으니까 is a very common mistake.
Summary
| Situation | Use |
|---|---|
| Command, request, suggestion | -(으)니까 |
| Past tense in the reason | -(으)니까 |
| Answering 왜? on its own | -(으)니까 (바빠서요 also works; only 니까 takes past) |
| Plain statement of cause | -아서 / -어서 |
| Apology or thanks | -아서 / -어서 |
Do not confuse it with
Taught alongside this
On the jabi learning path, this appears in 길이 막히니까 공연장까지 지하철로 갑시다 (Since the road is congested, let’s take the subway to the concert venue.) — Beginner Korean 1, Unit 18, on the theme of leisure. These come with it:
Words used above
Quick check
No sign-up, no score saved — just see if it stuck.
1. Which is correct: 'It's dangerous, so be careful.'
2. Someone asks 왜 안 왔어요? Which complete answer marks the past in the reason?
3. Which form is correct for 살다?
Common questions
Is -(으)니까 rude?
Not inherently, but it foregrounds your own reasoning, which can sound blunt or defensive in an apology or a refusal. In those situations -아서/어서 lands softer.
Can I use it with past tense?
Yes, freely — 했으니까, 갔으니까, 바빴으니까 are all normal. This is one of the cleanest differences from -아서/어서, which never takes past tense.
What about -(으)니 without 까?
-(으)니 is the same connector in a more formal or literary register. You will meet it in written Korean and in older speech; the meaning is the same.
Seen in the wild
Lessons where this pattern showed up in real Korean — news, slang, drama lines.
