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 ...'.
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.
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.
The reason he didn't come is that he was sick.
Directly uses the word 理由 (reason). More explicit and slightly formal.
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.
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.
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.
The reason I was late is that the train was delayed.
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.
I was late (explanatory tone).
The reason I didn't go is that I was tired.
The reason is that it's too expensive.