What I understand is that the の is used when an explanatory tone is needed,
but is there anything fundamentally different with these statments and which
is used when?
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2018-07-23T15:01:17.873
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2018-07-23T16:24:11.417
2018-07-23T15:39:13.940
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question
grammar explanatory-の
Whats the difference between なんで日本語を話せますか vs なんで日本語を話せるのですか
The former, なんで日本語を話せますか, is plain unnatural, and you should always construct
a sentence like the latter. A good rule of thumb is that なんで/どうして is almost
always used with explanatory の/ん.

Exceptions:

  * Short questions like "なぜか?", "なんでですか?" and "どうして?" do not require の/ん. (Although it's common to add な/の like "なぜなのか?", "なんでなんですか?", "どうしてなの?" The difference is very small.)
  * In an [embedded question](https://japanese.stackexchange.com/q/13034/5010), の/ん is not required.
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2018-07-23T16:24:11.417
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2018-07-23T16:24:11.417
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answer