んですが and differences in nuance with んです


I have read that when you use んです, you're implying that the listener already
knows what you're talking about and you're just kind of emphasizing the
conclusion. However, I have also seen some examples where んですが is used for a
situation that the listener is probably _not_ aware of, most notably:

> XXが苦手 **なんですが**

Example sentence from [this](http://soudan1.biglobe.ne.jp/qa3510185.html)
question:

> 私は歌を歌うのが苦手 **なんですが** 、どうやったらうまくなれますか???

The asker is posting in a QA forum where no one is aware that they're bad at
singing. They then go on to explain their exact circumstances _after_ they had
used なんですが. As I type this I realize that this is probably a retarded
question, but does んですが allow one to follow up with an explanation without any
implied foreknowledge, while plain んです requires said foreknowledge?




The explanation you first read is wrong.

You use のだ forms when what you are saying is background of the preceding
context, beside pseudo-imperative usage.

For examples, if you just ask if someone gives you something, you say
くれますか、くれませんか？ or so. On the other hand, when you see someone holding something
and reaching out his/her hand to you and you want to confirm if it's a gift
for you, you say くれるのですか？.

In your example, it would be also natural even if it was plain …苦手ですが… but the
speaker is feeling that the fact that she is bad at singing is reason or
background why she's asking there.




The explanation you first read is wrong.

You use のだ forms when what you are saying is background of the preceding
context, beside pseudo-imperative usage.

For examples, if you just ask if someone gives you something, you say
くれますか、くれませんか？ or so. On the other hand, when you see someone holding something
and reaching out his/her hand to you and you want to confirm if it's a gift
for you, you say くれるのですか？.

In your example, it would be also natural even if it was plain …苦手ですが… but the
speaker is feeling that the fact that she is bad at singing is reason or
background why she's asking there.

