-기 때문에
because of, owing to
The written way to give a reason. Heavier than -아서/어서 and, like it, unable to be followed by a command.
Build it
Pick a verb
When to use it
Attach -기 때문에 to any stem — no vowel rule, ㄹ stays. Unlike -기 on its own, this construction does take tense: 비가 왔기 때문에 못 갔어요.
It states a cause with more weight than -아서 and belongs in reports, essays, and formal explanation. In casual conversation it can sound like you are defending yourself.
With a noun, drop the -기: 비 때문에 늦었어요. Careful here — noun + 때문에 usually blames something, so 사람 때문에 means “because of that person” in a negative sense. For a neutral “because he is a student,” you need 학생이기 때문에.
Like -아서, it cannot be followed by a request or suggestion. That job belongs to -(으)니까.
How to attach it
| Situation | Form | Example |
|---|---|---|
| Any verb or adjective | -기 때문에 | 오다 → 오기 때문에 |
| Past | -았/었기 때문에 | 왔기 때문에 |
| 이다 | -이기 때문에 | 학생이기 때문에 |
| With a noun | noun + 때문에 | 비 때문에 |
| Sentence-initial | 그렇기 때문에 | 그렇기 때문에 중요합니다 |
| No command after | use -(으)니까 | 비가 오니까 우산을 가져가세요 |
In use
비가 왔기 때문에 행사가 취소됐어요.
The event was cancelled because it rained.
시간이 없기 때문에 자세히 설명할 수 없습니다.
Because there’s no time, I can’t explain in detail.
학생이기 때문에 할인을 받을 수 있어요.
You can get a discount because you’re a student.
교통사고 때문에 길이 막혔어요.
The road was blocked because of a traffic accident.
한국어를 배우고 싶었기 때문에 한국에 왔어요.
I came to Korea because I wanted to learn Korean.
그렇기 때문에 이 문제가 중요합니다.
That is why this issue matters.
Compared with
-아서/어서
Same restriction on commands, different weight. -아서 is the everyday choice; -기 때문에 is formal and can carry tense, which -아서 cannot.
비가 와서 못 갔어요. (speech) / 비가 왔기 때문에 가지 못했습니다. (writing)
-(으)니까
If the second clause tells someone to do something, neither -아서 nor -기 때문에 will work. Only -(으)니까 accepts commands and suggestions.
비가 오기 때문에 우산을 가져가세요. (wrong) / 비가 오니까 우산을 가져가세요. (right)
Noun + 때문에
With a bare noun the phrase tends to assign blame. To state a neutral fact about what something is, keep the 이기.
동생 때문에 늦었어요. (my brother made me late) / 동생이기 때문에 잘 알아요. (because he’s my brother, I know him well)
Watch out
비가 오기 때문에 우산을 가져가세요.
비가 오니까 우산을 가져가세요.
No request or suggestion may follow this ending. The restriction is the same as with -아서/어서.
학생 때문에 할인을 받을 수 있어요. — meaning “because I’m a student”
학생이기 때문에 할인을 받을 수 있어요.
Bare noun + 때문에 means “because of that person or thing,” often negatively. To say what someone is, use 이기 때문에.
친구를 만났어서 늦었어요.
친구를 만났기 때문에 늦었어요.
-아서 refuses tense, but -기 때문에 accepts it. If you need to mark the past on the reason, this is the ending that allows it.
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