説What you think and know
Explaining
のだ (often んです) asks for or gives an explanation of something you've both noticed. It adds warmth and involvement.
Plain fact, or explanation?
The same words feel different
My head hurts.
A statement of fact.
It's that my stomach hurts.
Explains something, like why you look unwell or are leaving.
Forms
の after a plain form
だ turns into な. Very casual speech uses んだ, or just の with a woman's or child's voice, or in questions.
| Before it | Formal | Conversational |
|---|---|---|
| Verb or い adjective | 行くのです | 行くんです |
| な adjective | 静かなのです | 静かなんです |
| Noun | 学生なのです | 学生なんです |
In use
Asking and explaining
What's wrong?
You've noticed something's up.
Where are you off to?
You've seen them leaving.
Actually, I'm going back home tomorrow.
Gives news as an explanation.
See, I don't have any money.
An excuse.
It's so amazing!
Sentence-final の is emotional and common among women and children.
When to use it
When there's something to explain
You need a shared reason to use it. If you see someone reading, 何を読んでいるんですか is natural, since you've both noticed it. But asking out of the blue, or stating plain facts with it, can sound pushy or strange. Don't overuse it in writing.
Drawing a conclusion
わけだ
You lived there ten years? No wonder your Japanese is so good.
You've reasoned it out from what you just heard.
If it's three hours a day, that means you study 21 hours a week.
A calculation.
わけだ vs. はずだ
Depends on context
That's why it's expensive.
わけだ needs something just said to work from.
They should have arrived by now.
はずだ can stand alone, based on what you know.
Check yourself
What is the speaker doing?
Your turn
な or だ?
It's that today's a day off.
Say it yourself
Noticing a friend
Your friend looks exhausted. Ask what's wrong. They explain they've been working at night. You conclude, “No wonder you're tired.”
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