understanding ～んです / ～なんです

[Guest]

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[Gordon]

First off, there are a couple of meanings of ~なんです. There's the one that means something "definitely is". But I'd like to talk about how to understand ～んです(or ～なんです for な-adjectives and nouns), which is means that whatever the person just said is an explanation, or that they're looking for an explanation.

...at least that's how it is described by my sensei and textbook. But I'm trying to come up with a way to understand it that might be a lot easier for English-speakers to grasp. I think it usually just means so/because/why. Maybe a synonym for から?

So, why were you late for class?
なぜ授業を遅れたんだの？ <- I guess this one gets some help from なぜ.

I'm sorry. (It was) because my bicycle broke.
すみません。自転車は壊したんです。

Do not be late, since it was an interruption.
遅れていけない。割り込みだったんだ。

Someone better at Japanese, please correct me if this sounds off-base. Does anyone else have a good way to explain this?

[sheepeater]

I talked about this last week with a native Japanese person at work. She got all confused and wasn't sure... <gulp>

[Aodh]

It has no meaning itself except to add emphasis.  There's no difference in meaning between なぜ遅れた？　and　なぜ遅れたんだ？　except the latter emphasizes that you really want to know why.  When used in a normal sentence, not a question, it just emphasizes that something happened or just something specific.

If you want an easy way to think about it, in English we add intonation to denote something important, this is the equivalent.  If you want to add "because/since", use ので instead.

Think about how you would say these two situations:

"What happened yesterday?"
昨日、何があったの？　　<< Inquisitive
"My bike broke."
自転車が壊した。


"Why were you late?!"
どうして遅れたんだ？！  << Inquisitive
"My bike broke."
自転車が壊したんだ。  << Explanation

Again, as a grammar point, んだ・なんだ are the spoken forms of のです・なのです, so you shouldn't have の after ~たんだ.　　Here are some ALC examples.  http://eow.alc.co.jp/%E3%81%9F%E3%82%93%E3%81%A0/UTF-8/