~기 때문(에)

Structurally this is a nominalization-based causal pattern: the nominalizer ~기 directly followed by the bound noun 때문 (“reason,” covered in §2.1.2.13). The register matters: ~기 때문(에) occurs more commonly in writing and formal speech than in casual conversation.

Two surface forms — depending on what 때문 takes next:

1. ~기 때문 + 에 + clause — “because X, Y”:

• 풍경이 멋지기 때문에 사람들이 많이 와요. (Many people come because the scenery is fantastic.)
• 불어를 몰랐기 때문에 문제를 많이 겪었어요. (Because I didn’t know French, I encountered a lot of problems.)

2. ~기 때문 + copula (~기 때문이다 / ~기 때문이에요 / ~기 때문이지요) — “it’s because X / the reason is X”:

• 풍경이 멋지기 때문이에요. (It’s because the scenery is fantastic.)
• 말로는 표현을 잘 못 하기 때문이지요. (That’s because he can’t express himself verbally.)

The two forms do different work. ~기 때문에 + clause delivers the cause and effect together in one sentence. ~기 때문이다 with the copula supplies the reason for something that has already been mentioned — typically as the answer to a “why” question or as a follow-up explanation:

A: 그런데 다른 애들을 왜 자꾸 때리는지 모르겠어요. (I don’t understand why he keeps hitting the other kids.)
B: 말로는 표현을 잘 못 하기 때문이지요. (That’s because he can’t express himself verbally.)

Or as a discursive move in writing:

만일 여자가 반장을 맡고 남자가 부반장이라면 어색하고 우스꽝스러운 이유는 무엇인가? 현실과 다르기 때문이다.
If we imagine a woman as leader and a man as her deputy, what makes this awkward and comical? The reason is precisely that it differs from reality.

How to attach it:

• Verb/adjective stem + ~기 때문에

  • 가다 → 가기 때문에
  • 없다 → 없기 때문에
  • 멋지다 → 멋지기 때문에

• Past tense → ~았/었기 때문에

  • 왔기 때문에, 몰랐기 때문에, 먹었기 때문에

• Future is typically formed with ~(으)ㄹ 거- (§4.3.2.2) → ~(으)ㄹ 것이기 때문에:

  • 이번 경기침체가 상당히 오래갈 것이기 때문에 상당수의 건설사 정리는 불가피합니다.
    (Because this economic slump is going to continue for a long time, the liquidation of a large number of construction firms is unavoidable.)

• Noun + 때문(에) (without ~기) is also possible — 때문 attaches directly to a noun:

  • 비 때문에 (because of the rain), 일 때문에 (because of work), 시험 때문에 (because of the exam)

Restrictions on use (these are not optional preferences — they govern when the pattern can be used at all):

1. No commands, proposals, suggestions, invitations, or requests in the second clause.

Like ~아/어서, 기 때문에 cannot precede these speech acts. If the second clause is “so let’s…”, “so do X”, “so please do X”, “so why don’t we…”, switch to **(으)니까** instead.

• ✗ 비가 오기 때문에 우산을 가져가세요. (awkward — request after ~기 때문에)
• ✓ 비가 오니까 우산을 가져가세요. (use ~(으)니까 for the imperative)

2. No thanks, apologies, or excuses.

This is where ~기 때문에 differs from ~아/어서. ~아/어서 (not ~기 때문에) is the form used with expressions of thanks, apology, and giving excuses:

• ✓ 도와주셔서 감사합니다. (Thank you for helping.) — ~아/어서
• ✗ 도와주시기 때문에 감사합니다. (sounds wrong)
• ✓ 늦어서 죄송합니다. (Sorry for being late.) — ~아/어서
• ✗ 늦었기 때문에 죄송합니다. (sounds wrong)

Use ~아/어서 for “thank you for…,” “sorry for…,” “the reason I [excuse]…”

3. ~기 때문에 has no problem with reverse-order events. ~아/어서 does.

~아/어서 sounds awkward when the second-clause event actually happens before the first-clause event in real time. ~기 때문에 has no such restriction. So for sentences where the effect temporally precedes the cause, ~기 때문에 is preferred:

• 수업이 10시에 시작하기 때문에 집에서 9시 반에 나와요. (Since class starts at 10, I leave the house at 9:30.) — leaving (9:30) happens before the class start (10), but you reason backward from the start time.

Trying 수업이 10시에 시작해서… here is awkward because ~아/어서 wants the cause to precede the effect in time, and 9:30 is earlier than 10:00.

Tip: Reach for ~기 때문에 in writing, formal speech, and explanatory contexts; reach for ~아/어서 for thanks/apology/excuses; reach for ~(으)니까 when the second clause is a command, proposal, suggestion, invitation, or request. The ~기 때문이다 (copula) form is the workhorse for academic and journalistic writing — “the reason is X” is exactly how Korean prose lays out causal explanation.