-(으)니까 (eunikka) - Because/Since | Korean Grammar Documentation

The connective ending -(으)니까 (eunikka) expresses causality with emphasis, showing that the first clause is a strong reason or justification for the second. It's particularly used with commands, suggestions, and statements requiring justification.

Basic Function

-(으)니까 expresses a strong reason, cause, or justification for the following clause.

Translation: because, since, as (emphatic)

Usage: Emphasizing reasons, justifying commands/suggestions

Formation

After Vowels or ㄹ: -니까

가다 → 가니까 (because go)
크다 → 크니까 (because big)
멀다 → 먼니까 (because far)
예쁘다 → 예쁘니까 (because pretty)

After Consonants: -으니까

먹다 → 먹으니까 (because eat)
작다 → 작으니까 (because small)
좋다 → 좋으니까 (because good)
없다 → 없으니까 (because not exist)

With Past Tense: -았/었으니까

Unlike -아/어서, -(으)니까 CAN take past tense:

먹다 → 먹었으니까 (because ate)
가다 → 갔으니까 (because went)
좋다 → 좋았으니까 (because was good)

Key Difference from -아/어서

Can Use with Commands/Suggestions

This is the main difference:

✓ 춥으니까 코트를 입으세요. (Since it's cold, wear a coat.) - command allowed

✓ 시간이 없으니까 빨리 갑시다. (Since we don't have time, let's go quickly.) - suggestion allowed

❌ 추워서 코트를 입으세요. (incorrect - can't use -아/어서 with commands)

Stronger Emphasis on Reason

-(으)니까 emphasizes the causality more strongly:

비가 오니까 못 가요. (Since it's raining, I can't go.) - emphasizes the rain as reason
비가 와서 못 가요. (Because it's raining, I can't go.) - neutral statement

With Commands (Imperative)

Pattern: Reason니까 [Command]

Justifying commands:

위험하니까 조심하세요. (Since it's dangerous, be careful.)
늦었으니까 빨리 가세요. (Since you're late, go quickly.)
춥으니까 창문을 닫으세요. (Since it's cold, close the window.)
시끄럽으니까 조용히 하세요. (Since it's noisy, be quiet.)

With Suggestions (Propositive)

Pattern: Reason니까 [Suggestion]

Justifying suggestions:

날씨가 좋으니까 산책합시다. (Since the weather is nice, let's take a walk.)
시간이 있으니까 영화 봅시다. (Since we have time, let's watch a movie.)
배가 고프니까 밥을 먹읍시다. (Since we're hungry, let's eat.)
피곤하니까 쉽시다. (Since we're tired, let's rest.)

Strong Reasons and Justifications

Emphasizing Causality

When you want to strongly emphasize the reason:

사실이니까 믿으세요. (Since it's true, believe it.)
중요하니까 잘 들으세요. (Since it's important, listen carefully.)
약속했으니까 지켜야 해요. (Since I promised, I must keep it.)

With Past Tense

Pattern: -았/었으니까

Can use past tense in the reason clause:

공부했으니까 시험을 잘 볼 거예요. (Since I studied, I'll do well on the exam.)
먹었으니까 배가 안 고파요. (Since I ate, I'm not hungry.)
일찍 일어났으니까 피곤해요. (Since I woke up early, I'm tired.)
비가 왔으니까 길이 젖었어요. (Since it rained, the road is wet.)

Explaining Discoveries

Pattern: Discovery니까 [Reaction]

When explaining something you discovered:

열어 보니까 비어 있었어요. (When I opened it, it was empty.)
가 보니까 문이 닫혀 있었어요. (When I went, the door was closed.)
먹어 보니까 맛있었어요. (When I tried it, it was delicious.)
생각해 보니까 맞는 것 같아요. (Now that I think about it, it seems right.)

This uses -(으)니까 to connect the action with the discovered result.

Irregular Verbs

ㅂ Irregular

ㅂ stays before -(으)니까:

춥다 → 춥으니까 (since it's cold)
덥다 → 덥으니까 (since it's hot)
아름답다 → 아름답으니까 (since it's beautiful)

Note: Some sources show these can also become 추우니까, 더우니까.

ㅎ Irregular

ㅎ stays before -(으)니까:

빨갛다 → 빨갛으니까 (since it's red)
하얗다 → 하얗으니까 (since it's white)
그렇다 → 그렇으니까 (since it's so)

Can also be: 빨가니까, 하야니까, 그러니까

으 Irregular

으 stays before -니까:

크다 → 크니까 (since it's big)
예쁘다 → 예쁘니까 (since it's pretty)
바쁘다 → 바쁘니까 (since busy)

ㄹ Irregular

ㄹ drops before -니까:

알다 → 아니까 (since know)
살다 → 사니까 (since live)
만들다 → 만드니까 (since make)
멀다 → 머니까 (since far)

ㄷ Irregular

ㄷ → ㄹ, then drops:

듣다 → 들으니까 (since listen/hear)
걷다 → 걸으니까 (since walk)

Wait, let me correct: after ㄹ, use -니까 (no 으):

듣다 → 들으니까 becomes 드니까 (ㄹ drops before ㄴ)

Actually, ㄷ irregular:

듣다 → 들- → 드니까 (ㄹ drops before ㄴ)
걷다 → 걸- → 거니까 (ㄹ drops before ㄴ)

ㅅ Irregular

ㅅ drops before vowel:

낫다 → 나으니까 (since better/healed)
짓다 → 지으니까 (since build)

Common Expression: 그러니까

Standalone "Therefore/So"

그렇다 + -(으)니까 = 그러니까

Used as standalone conjunction:

비가 와요. 그러니까 우산을 가져가세요. (It's raining. So take an umbrella.)
중요해요. 그러니까 잘 들으세요. (It's important. So listen carefully.)

Can also mean "I mean" or "You see" in conversation:

그러니까, 제 말은... (So, what I mean is...)

Giving Advice

Pattern: Reason니까 [Advice]

Strong justification for advice:

위험하니까 조심하세요. (Since it's dangerous, be careful.)
어렵으니까 도움을 받으세요. (Since it's difficult, get help.)
늦었으니까 서두르세요. (Since you're late, hurry.)

Making Requests

Pattern: Reason니까 [Request]

Justifying requests:

무겁으니까 도와주세요. (Since it's heavy, please help.)
시간이 없으니까 빨리 해 주세요. (Since there's no time, please do it quickly.)
중요하니까 확인해 주세요. (Since it's important, please check.)

Expressing Certainty

Confident Statements

When you're certain about the reason:

사실이니까 걱정하지 마세요. (Since it's true, don't worry.)
제가 확인했으니까 틀림없어요. (Since I checked, there's no mistake.)
준비했으니까 괜찮을 거예요. (Since we prepared, it'll be okay.)

Warnings

Pattern: Warning Condition니까 [Consequence/Advice]

미끄럽으니까 조심하세요. (Since it's slippery, be careful.)
뜨겁으니까 만지지 마세요. (Since it's hot, don't touch it.)
위험하니까 가까이 가지 마세요. (Since it's dangerous, don't go close.)

Permissions and Prohibitions

Granting Permission

끝났으니까 가도 돼요. (Since it's finished, you may go.)
시간이 있으니까 천천히 해도 돼요. (Since there's time, you may do it slowly.)

Prohibitions

늦었으니까 서두르지 마세요. (incorrect logic)
늦었으니까 서두르세요. (correct - hurry)

Contrast with -아/어서

-(으)니까 (Stronger)

Used with commands/suggestions ✓
Can use past tense ✓
Emphasizes reason more
More direct causality
Sounds more definite

Example:

비가 오니까 우산을 가져가세요. (Since it's raining, take an umbrella.) - command

-아/어서 (Softer)

Cannot use with commands/suggestions ✗
Cannot use past tense ✗
More neutral
More about natural sequence
Softer, conversational