Grammar
-기 때문이다
Meaning
Advanced-gi ttaemunida
Used at the end of a sentence to state a reason, meaning '(it is) because ~.' It presents the previous statement's cause or explanation. The related connective form -기 때문에 is used mid-sentence to link a reason clause to a result clause.
Form
Attaches to a verb or adjective stem: stem + -기 때문이다. Past tense: stem + -았/었기 때문이다. A noun can also be the reason without -기, using N(이) 때문이다 directly (e.g., 비 때문이다 = 'it's because of the rain'). -기 때문이다 is common in formal or written explanations, often answering an implied 'why?'.
Examples
조사한 지 100년이 되는 해였기 때문입니다.
It is because it was the year marking 100 years since the survey began.
매출이 줄어든 것은 경기가 나빠졌기 때문이다.
Sales fell because the economy worsened.
그가 늦은 이유는 길이 막혔기 때문이다.
The reason he was late is that traffic was heavy.
값이 오른 것은 원자재 가격이 상승했기 때문입니다.
Prices rose because raw material costs went up.
Common mistakes & nuance
This is a two-sentence pattern: the first sentence states a fact, and the -기 때문이다 sentence explains it, often opening with 이는 or 그 이유는. News writing leans on it because the reason gets to stand as its own sentence. Do not end a sentence with -기 때문에 — that form only connects clauses and leaves the sentence unfinished.
Similar grammar
- 때문에
-기 때문이다 goes at the end of a sentence, stating the reason as the sentence's main point ('it is because ~'). 때문에 (or -기 때문에 with a clause) sits mid-sentence, linking a cause to the result that follows.
- N이라서
N이라서 gives a reason based on a noun+이다 ('because it is N') and is common in speech. -기 때문이다 attaches to a full verb/adjective clause and is more formal, typically at the end of a written explanation.