なぜなら～からThe reason is that...
なぜなら～から presents a conclusion or claim first, then clearly introduces the reason supporting it. It is especially useful when you want the structure of an explanation to be unmistakable.
How the explanation is organized
First state the conclusion that needs support. Then use なぜなら to announce that the explanation is coming, and close that explanation with からだ, からです, or formal からである. The reason should add genuine support rather than merely restating the conclusion.
A clear conclusion followed by support
この案を採用すべきです。なぜなら、費用を二割減らせるからです。
We should adopt this proposal. The reason is that it can reduce costs by twenty percent.
AnalyzeThe first sentence gives the recommendation; the second supplies concrete support for it.
Plain, polite, and formal endings
Choose the final ending to match the overall style of the explanation.
この調査は来月まで続けるべきだ。なぜなら、今のデータだけでは結論を出せないからだ。
We should continue this study until next month. The reason is that the current data is not enough to reach a conclusion.
Analyze会議はオンラインで行います。なぜなら、参加者の半数が海外にいるからです。
The meeting will be held online. The reason is that half of the participants are overseas.
Analyzeこの制度は見直す必要がある。なぜならば、現在の規定では利用できない人が多いからである。
This system needs to be reviewed. The reason is that many people are unable to use it under the current rules.
AnalyzeConnective or explicit why-question frame?
Use なぜなら as a connective after a conclusion when you simply want to announce its supporting reason. By contrast, the pattern built with なぜ or どうして + かというと explicitly sets up or echoes a why-question before giving the answer.
More examples
明日の屋外イベントは延期します。なぜなら、強い雨が予想されているからです。
Tomorrow's outdoor event will be postponed. The reason is that heavy rain is forecast.
Analyze今は契約を更新しないほうがよい。なぜなら、来月から条件が変わるからだ。
It would be better not to renew the contract now. The reason is that the terms will change next month.
Analyze私はこの計画に賛成です。なぜなら、地域の雇用を増やせるからです。
I support this plan. The reason is that it can increase local employment.
Analyzeこの本は初級者には勧めません。なぜなら、専門用語の説明がほとんどないからです。
I do not recommend this book for beginners. The reason is that it provides almost no explanation of technical terms.
Analyzeこの結果だけで安全だとは判断できない。なぜなら、試験の回数がまだ少ないからである。
We cannot conclude from this result alone that it is safe. The reason is that too few tests have been conducted so far.
Analyze発表では最初に結論を述べます。なぜなら、そのほうが聞き手に要点が伝わりやすいからです。
In a presentation, I state the conclusion first. The reason is that this makes it easier for the audience to grasp the main point.
Analyze