Translation guide
This phrase introduces an explanation or cause. In Japanese, it is often expressed with sentence-ending patterns or conjunctions that mark the preceding statement as the reason.
The speaker states a fact or situation and then explains why it happened or why it is the case.
A common pattern where the first clause nominalized with の is the result, and the second clause with から gives the reason. Literally 'The reason that ... is because ...'.
遅れたのは電車が遅れたからだ。
The reason I was late is that the train was delayed.
The reason he is angry is that I broke my promise.
Used to state a fact, then explicitly give the reason. なぜなら means 'because' or 'the reason is'. Often used in writing or formal speech.
私はその計画に反対です。なぜなら、費用がかかりすぎるからです。
I am against the plan. The reason is that it costs too much.
Similar to のは…からだ, but uses というのは to emphasize the explanation. Often used when clarifying a statement.
彼が来なかったというのは、病気だったからだ。
The reason he didn't come is that he was sick.
Directly uses the word 理由 (reason). More explicit and slightly formal.
遅刻した理由は、寝坊したからです。
The reason I was late is that I overslept.
In casual speech, the reason is often given with simple conjunctions or sentence-ending particles.
The explanatory のだ/んだ pattern. It can imply 'the reason is' when used after a statement. Very common in spoken Japanese.
遅くなってごめん。電車が遅れたんだ。
Sorry I'm late. The reason is that the train was delayed.
Simply ending a sentence with から gives the reason. Often used when the result is already understood from context.
電車が遅れたから。
Because the train was delayed. (implying 'that's why I'm late')
…のは…からだ explicitly states both the result and the reason, while …からだ often omits the result when it's obvious. Use the full pattern for clarity or emphasis.
遅れたのは電車が遅れたからだ。
The reason I was late is that the train was delayed.
電車が遅れたからだ。
Because the train was delayed.
Direct translations like '理由は…です' can sound stiff or unnatural in casual speech. Use explanatory のだ or から patterns instead.
遅れたんだ。
I was late (explanatory tone).
行かなかったのは疲れていたからだ。
The reason I didn't go is that I was tired.
高すぎるからです。
The reason is that it's too expensive.