Is んでしょう（か） grammatical, and what does it mean?

Question

I've learned that んですか can be used to check an educated guess, as in:

(upon seeing someone dragging a piece of luggage)

ねえ、旅行するんですか。 Hey, you're going to travel, aren't you?

I've also learned that でしょう　can be used to express an educated guess, the validity of which can be checked with ね — or self-doubted by か or a rising tone:

雨が　ふるでしょう。 It's probably going to rain.

雨が　ふるでしょうね。 It's probably going to rain, isn't it?

http://ejje.weblio.jp/content/%E3%81%A7%E3%81%97%E3%82%87%E3%81%86%E3%81%AD

雨が　ふるでしょうか。 I wonder if it's going to rain?

http://japanese.about.com/library/weekly/aa093000.htm

What I want to ask is if んでしょう or んでしょうか can be used, and if so, what their connotations are. Google shows they exist, but are they part of standard Japanese?

Answer 1

They're definitely part of standard Japanese, and I don't see why they wouldn't be. Their nuance is different, though, from でしょう（か） on its own: like のだ in general, they have an explanatory tone. 雨が降るでしょう could be 'I think it will rain' or on the weather forecast, just 'It will rain'. 雨が降るんでしょう could be a response to どうして来ないんですか？ 'Why won't you come?' 'It's probably going to rain.' And でしょうか is not just 'I wonder' but also a polite question - you could say すみませんが行けません 'I'm afraid I can't go', and the response could be どうして？時間が少ないんでしょうか? 'Why? Do you not have the time?' Take note that, more formally, you should definitely say のでしょう rather than んでしょう.