Hi everybody.

When looking or listening to real japanese I often hear frases like this

^Poteto nan desu^ I would translate this as ^It is potatoes^
But i would also translate ^Potato desu^, as ^It is potatoes^.

I can not tell the difference between these two sentences. I have looked in my grammar book but cant find anything on this. The more i think about it I begin to wonder if ^Poteto nan desu^, should not be translated into something like ^Potatoes is what it is^. And that it is used when explaining something.

I would be glad if someone could help me because I hear it all the time and its eating away at me at nights and i cant sleep or eat or ....

As I understand it, ポテトなんです　is a contraction of ポテトなのです, which essentially does mean "it's a potato", but has an explanatory tone. In a few places I've seen it glossed as "It's that it's a potato", which is not far from your "Potato is what it is". I think "ポテトですから" is similar in meaning.

Following on from shaydwyrm, you should look up "~のです" in your grammar book and you should find an entry. I've always had trouble with the construction since there's no English equivalent. I wouldn't bother trying to think of a way of translating it, I'd just try to understand it. It's extremely common and if you encounter it enough then you pick up the gist.

Thanks for your answers! That clear things up、 but probably, as you say no idea to dwell on details, if your understand the gist of it。

ありがとう！