connective N3 common casualpolitewritten
のだから — because (as you know) ~
のだから
Builds on のだ
Meaning
- because (as we both know) ~ / since ~ — gives a reason the speaker treats as obvious or established, to back up an assertion or push
Key sentence
子供なのだから、失敗しても仕方がない。
Since they're just a child, mistakes can't be helped.
Formation
| Attaches to | Form | Example |
|---|---|---|
| Plain form + のだから (casual んだから) | Plain + の（ん）だ + から | 約束したのだから (since you promised) |
Examples
もう大人なんだから、自分で決めなさい。
You're an adult now, so decide for yourself.
彼が約束したのだから、きっと来るだろう。
Since he promised, he'll surely come.
When you can't use it
- Because the reason is framed as already-known, the main clause is typically an assertion, demand, or judgment — 〜なさい, 〜べきだ, 〜はずだ, 〜に決まっている — not a neutral statement.
Easily confused with
Notes
- The casual form is んだから. The related sentence-final んだもん／だもの is a softer, more childlike self-justifying 'because.'
See のだから in real sentences
Jengo shows のだから the way you actually meet it: inside real Japanese sentences, so it sticks instead of staying an abstract rule.
Study it in JengoSources Compiled with reference to A Dictionary of Advanced Japanese Grammar.