Because: ~(으)니까 (Reason with Commands and Discovery)

Overview

~(으)니까 is a powerful connector that means "because" or "since." It shares some territory with ~아/어서 but has unique abilities:

1. Can be used with commands and suggestions (unlike ~아/어서)
2. Can take past tense on the first clause (unlike ~아/어서)
3. Can express discovery -- finding something out upon doing something
4. Has a stronger, more assertive tone than ~아/어서

How to Form ~(으)니까

Wait -- ㄹ behaves specially. When a suffix starting with ㄴ, ㅂ, or ㅅ follows ㄹ, the ㄹ drops:

With past tense

~(으)니까 allows past tense on the first clause. Add ~았/었 before ~으니까:

Part 1: Reason with Commands and Suggestions

The primary advantage of ~(으)니까 over ~아/어서 is that it works with commands and suggestions.

With commands (~세요, ~(으)십시오)

• 추우니까 옷을 입으세요. (It's cold, so please put on clothes.)
• 위험하니까 조심하세요. (It's dangerous, so please be careful.)
• 시간이 없으니까 빨리 하세요. (There's no time, so please hurry.)
• 비가 오니까 우산 가져가세요. (It's raining, so take an umbrella.)

With suggestions (~자, ~(으)ㅂ시다)

• 배고프니까 밥 먹자. (I'm hungry, so let's eat.)
• 날씨가 좋으니까 산책합시다. (The weather is nice, so let's take a walk.)
• 시간이 있으니까 영화 보자. (We have time, so let's watch a movie.)
• 늦었으니까 택시 탑시다. (We're late, so let's take a taxi.)

Compare with ~아/어서

Part 2: Discovery / Realization

~(으)니까 can express that you discovered or realized something upon doing an action. This is a meaning that ~아/어서 does not have.

• 가 보니까 아무도 없었어요. (When I went and looked, nobody was there.)
• 먹어 보니까 맛있었어요. (When I tried eating it, it was delicious.)
• 해 보니까 어렵지 않았어요. (When I tried doing it, it wasn't difficult.)
• 만나 보니까 좋은 사람이었어요. (When I met them, they were a nice person.)

This pattern often combines with ~아/어 보다 (to try doing):

Verb stem + 아/어 보니까 = "When I tried [verb]-ing, (I found that)..."

Part 3: Strong Emphasis on Reason

~(으)니까 carries a more assertive, emphatic tone than ~아/어서. It is often used when the speaker wants to strongly justify or persuade.

• 제가 했으니까 걱정하지 마세요. (I did it, so don't worry.)
• 내가 할 거니까 신경 쓰지 마. (I'll do it, so don't bother.)
• 벌써 끝났으니까 됐어요. (It's already over, so that's enough.)

In spoken Korean, ~(으)니까 is sometimes shortened to ~(으)니까 → ~(으)니:

• 가니 (because I go)
• 먹었으니 (because I ate)

And in very casual speech, it can become ~(으)니깐 or ~(으)니:

• 추우니깐 들어가자. (It's cold so let's go in.)

~(으)니까 vs. ~아/어서: Complete Comparison

When to choose which

• Giving a soft reason: ~아/어서

• 피곤해서 일찍 잤어요. (I was tired so I slept early.)

• Giving a reason with a command or suggestion: ~(으)니까

• 피곤하니까 일찍 자세요. (You're tired, so sleep early.)

• Expressing discovery: ~(으)니까

• 가 보니까 정말 좋았어요. (When I went, it was really great.)

~(으)니까 in Questions

~(으)니까 can also be used when asking questions:

• 이미 했으니까 또 해야 돼요? (I already did it, so do I have to do it again?)
• 아니까 왜 또 물어봐요? (You know it, so why are you asking again?)

Common Mistakes

Summary

1. ~(으)니까 means "because/since" with a strong, assertive nuance.
2. Unlike ~아/어서, it works with commands and suggestions.
3. Unlike ~아/어서, it allows past tense on the first clause.
4. It has a unique discovery meaning: "when I did X, I found that Y."
5. Formation: vowel stem + 니까, consonant stem + 으니까, ㄹ stem drops ㄹ + 니까.
6. In casual speech, often shortened to ~(으)니 or ~(으)니깐.