Hot answers tagged keigo
I don't think なん is particularly formal. It's short for なの. If I understand the traditional grammar right, な here is analyzed as 断定の助動詞「だ」の連体形「な」, a form which appears chiefly before the 形式名詞「の」 in constructions such as 「〜なのだ」「〜なので」「〜なのに」「〜なのか」 and so on. I think it's like this: どこだ ＋ のだ ＝ どこなのだ So the difference in meaning is the same you get from ...
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