What's up with "なのです"?

[gerald_ford]

Not sure if I am making a big deal out of nothing, but I often sentences like:

adjective/noun + です。

as in:

必要です。

But then I also hear sentences like:

adjective/noun + なのです。

Like:

必要なのです。

I asked my wife what the difference is between the two, and she thought it was the same. It seems to be that way too, based on what I can read. So my question is is are they really the same, and if so, why add the なの in the first place? When would one even do this?

Thanks!

[Belton]

It's an explanatory form. Or used to elicit empathy. You might be more familiar with it as んです。

http://www.guidetojapanese.org/particles3.html#part5
http://japanese.about.com/blqow24.htm

[gerald_ford]

Ha ha ha, I even looked on the first URL there (the Guide to Japan one), yesterday hoping to find this, and couldn't. Obviously I didn't look carefully enough. Thanks much!

[Bucko]

adjective/noun + なのです。

Like:

必要なのです。

の or ん is often used when you're explaining something and can be translated as "it" in the sense of "it is that...". The な part is the regular な you use with adjectives, so in actual fact の/ん is an adjective.

You'd use 必要なのです in the following situation:
Person A: Why do we have to do that???
Person B: 必要なのです (well, it's just that it's necessary *shrugs*)

Other variations of it are:
んだ
なんだ
なのである
なんです
etc etc