때문에: Because of

때문에 ttaemune: because of, and the blame it carries

때문에 ttaemune gives the reason for something. It's straightforward to attach and there are two things about it that catch people out: what it connects to, and how it sounds.

With a noun

Attach it directly. Nothing changes.

• 비 때문에 못 갔어요. bi ttaemune mot gasseoyo — "I couldn't go because of the rain."
• 너 때문에 늦었어. neo ttaemune neujeosseo — "I was late because of you."

With a verb, you need 기

This is the mistake worth fixing early. 때문에 ttaemune can't attach straight to a verb — you have to turn the verb into a noun first with 기.

• 비가 왔기 때문에 못 갔어요. biga watgi ttaemune mot gasseoyo — "Because it was raining, I couldn't go."
• 바쁘기 때문에 못 가요. bappeugi ttaemune mot gayo — "I can't go because I'm busy."

So: noun + 때문에 ttaemune, but verb stem + 기 때문에 gi ttaemune. Skipping the 기 is one of the most common intermediate errors.

It sounds like blame

This is the part that isn't in most explanations, and it matters socially.

때문에 ttaemune points a finger. 너 때문에 neo ttaemune · "because of you" is an accusation, not a neutral statement of cause. Used about a person, it almost always carries fault.

When the cause is positive, Korean switches particles entirely and uses 덕분에 (*deokbune*) deokbune · "thanks to":

• 너 때문에 늦었어 neo ttaemune neujeosseo. — "I was late because of you." Your fault.
• 네 덕분에 성공했어. ne deokbune seonggonghaesseo — "I succeeded thanks to you." Your credit.

Same grammatical slot, opposite emotional load. For credit, 덕분에 deokbune is the natural choice. 때문에 ttaemune is neutral, but it often sounds like blame, especially when it's about a person. Using 덕분에 deokbune for something bad sounds sarcastic.

때문에 ttaemune vs 아/어서 vs (으)니까

Three ways to say "because", and they aren't interchangeable.

• 때문에 ttaemune — states a cause, fairly formal, and can assign blame.
• 아/어서** — the everyday "so", neutral. Can't be used with commands or suggestions.
• (으)니까** — reason plus judgment, and it's the one you use before a command.

• 비가 오니까 우산을 가져가세요. bi-ga onikka usan-eul gajyeogaseyo — "It's raining, so take an umbrella." ✓
• 비가 와서 우산을 가져가세요 biga waseo usaneul gajyeogaseyo. ✗

That restriction on 아/어서 is the practical reason to learn all three rather than picking a favorite.

Ending a sentence with 때문이다

때문에 can also close a sentence as 때문이에요 ttaemunieyo, "it's because …". This is how you explain a reason after the fact, often with 왜냐하면 waenyahamyeon, "the reason is", at the start:

• 늦은 건 길이 막혔기 때문이에요. neujeun geon giri makyeotgi ttaemunieyo "The reason I'm late is that the traffic was bad."
• 왜냐하면 시간이 없었기 때문이에요. waenyahamyeon sigani eopseotgi ttaemunieyo "That's because I didn't have time."

"Because I'm a student": 이기 때문에

Careful with nouns. Noun + 때문에 means "because of that thing". To say "because I am X", add 이다 ida first and use the verb form:

• 학생이기 때문에 할인을 받았어요. haksaengigi ttaemune harineul badasseoyo "I got a discount because I'm a student."
• 학생 때문에 회의가 늦어졌어요. haksaeng ttaemune hoeuiga neujeojyeosseoyo "The meeting got delayed because of a student."

Same noun, completely different meaning.