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How To Say "Because" In Korean | -기 때문에 vs 아/어서 vs (으)니까

Updated: Jul 19, 2023

Hello, It's KoreanStudyJunkie! In this post I will talk about the different grammar structures used to express reasons in Korean. This is a long post, so stick around to learn more.

(기) 때문에

-때문에 & -기 때문에 can both be translated to “because” in English. They are used to express the reason or the cause of a situation mentioned in the second sentence.

-기 때문에 is used when expressing a clear reason and is a more literary expression than -아/어서 and (으)니까.

Okay, but why are there 2 different forms?

Nouns + 때문에

Verbs/Adjectives + 기 때문에

Other forms:

Past Tense - ~았/었기 때문에

the clause before ~기 때문에 can be conjugated to the past tense. In these cases, ~기 should be added directly to the addition of ~았/었.

[폰이 없었기 때문에 연락하지 못했어요.

Because I didn’t have my phone, I couldn’t contact you. ]

Future Tense - ~ㄹ 것이기 때문에 | shortened: ㄹ 거기 때문에

Adding ~기 때문에 to a word conjugated in the future tense is simply a matter of attaching ~기 때문에 to the 이다 at the end of this future tense conjugation.

[나중에 먹을 것이기 때문에 지금 먹고 싶지 않아.

Because I’ll eat later, I don’t want to eat now.]


-기 때문에 cannot be used in imperative or propositive sentences

*basically no commands, suggestions, or let’s.. type of sentences

(Instead you could use -니까 for those sentences)

[Example: 날씨가 춤기 때문에 따뜻한 옷을 입으세요. (X)

날씨가 추우니까 따뜻한 옷을 입으세요 (✔️)


This grammar has a separate usage that has a meaning like ‘and’ or ‘in order to’. For example, I peeled a banana (in order to)and ate it. We won’t focus on it in this lesson.

Now on to the main usage:

to Indicate the reason for the succeeding event = “because (of)” / “so that…” in English.

[배고파서 먹고 싶어요.]

Why do I 먹고 싶어요? Because 배고파서..

Before nouns the form changes to (이)라서

소파라서 무거워요. > It’s heavy, because it’s a sofa.


Can not be used in imperative or propositive sentences (as in making commands, requests, suggestions, or saying “let’s do..” is not to happen with this grammar)

  • (으)니까 can be used with those (so with grammar like: 세요, ㄹ까요., 자, ㅂ시다)

Tense markers such as -았/었- and -겠- can not come before -아/어서

(으)니까 (shortened form: (으)니)

-으니까 is one of the most common ways of saying “because” or “so” in Korean. The second part of the sentence (the part that comes before this grammar pattern) is the basis for the first part of the sentence (what comes after it).

It can be used with verbs, adjectives, and nouns, as well as the past tense (았/었/했) and future tense (겠). It is also common to end a sentence with ~(으)니까(요).

-으니까 also has another usage - to express a realization after doing something. This usage often translates to “when” but we won’t focus on that in this lesson. [ 학교에 가니까 아무도 없었다.

= When I went to school, (I realized) there was nobody there.]


아/어/해서 vs (으)니까 vs 때문에

The biggest and most notable difference between the two is that ‘어서‘ can not be used with propositive (suggesting an action) or imperative (requesting or commanding an action) sentences, while 으니까 can. Remember 때문에 follows this same rule as well.

[Example: 배가 고파서 빨리 오세요 (X)

배가 고프니까 빨리 오세요 (✔️)

= I’m hungry so please come fast. ]

(으)니까 can not be used in common greetings and certain common expression. This same rule goes for 때문에. Use 어/아서 instead, for example:

만나서 반갑습니다 (O) | 만나니까 반갑습니다 (X)

= Nice to meet you.

늦게 와서 미안해요 (O) | 늦게 왔으니까 미안해요 (X)

= Sorry for being late.

You can not use past (았/었/였) and future (겠) tenses with 어서 / 아서 / 해서.

You can talk about something that happened in the past or happens in the future, but you can not use tense markers right before it. However, with (으)니까, you can!

먹었으니까 (O) | 먹었어서 (X)

= because I ate…



(기) 때문에

비 때문에 차가 많이 막혔어요.

There was a lot of traffic due to the rain.

금요일은 친구 생일이기 때문에 만날 수 없어요.

Friday is my friend’s birthday, so I won’t be able to meet.

저는 바고프기 때문에 밥을 먹고 싶어요.

I want to eat because I am hungry.


밥을 많이 먹어서 배가 아파요.

I ate a lot so that my stomach hurts.

(notice: the past tense form is not used, but from the context we know that it happened in the past)

그 옷은 작아서 못 입어요.

Those clothes are small so that I can't wear them.


비가 오니까 택시를 탑시다.

Because it’s raining, let’s take a taxi.

제가 숙제를 다 했으니 이제 영화를 볼 수 있어요.

I finished all my homework, therefore I can watch movie now.

위험하니까 조심하세요.

It’s dangerous so be careful.

That's all for today's post. I hope you learned something new. There are actually EVEN MORE ways to say "because" in Korean. Here is another lesson on a few more Intermediate forms of because.

If you'd like to see more grammar explanations like this, check out my grammar books - here!

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