connective N3 common politewritten
なぜなら — the reason is (because) ~
なぜなら
Meaning
- the reason is that ~ / this is because ~ — a formal sentence-opener introducing the reason for the previous statement
なぜなら starts a *new sentence* that explains the one before it, and it typically closes with からだ / ためだ: 行けない。なぜなら、仕事があるからだ ('I can't go. The reason is I have work'). It's explicit and somewhat formal — common in essays, presentations, and logical argument. から/ので embed the reason inside one sentence; なぜなら sets it out as a separate, signposted clause. なぜならば is the fuller, stiffer variant.
Key sentence
私は反対だ。なぜなら、危険すぎるからだ。
I'm against it — the reason being that it's too dangerous.
Formation
| Attaches to | Form | Example |
|---|---|---|
| Sentence-initial; the explaining clause usually ends in からだ／ためだ | (statement)。なぜなら、〜からだ。 | なぜなら、〜からだ / なぜならば、〜ためである |
Examples
計画は延期された。なぜなら予算が足りなかったからだ。
The plan was postponed, because the budget fell short.
運動は大切だ。なぜなら、健康を保つからである。
Exercise is important, because it keeps you healthy.
彼を信頼している。なぜなら、一度も嘘をついたことがないからだ。
I trust him, because he has never once lied.
Easily confused with
〜から から packs the reason into the same sentence ('because X, Y'); なぜなら opens a separate sentence to spell the reason out, more explicit and formal, and pairs with a closing からだ. だから Opposite order of logic: だから introduces the *result* ('so, therefore ~'); なぜなら introduces the *reason* ('this is because ~'). Result-first vs reason-first.
Notes
- The closing からだ/ためだ is expected — leaving it off (なぜなら、危険だ) sounds incomplete in careful writing. なぜかというと is the more conversational equivalent.
See なぜなら in real sentences
Jengo shows なぜなら the way you actually meet it: inside real Japanese sentences, so it sticks instead of staying an abstract rule.
Study it in Jengo