I'm not sure when should I use particle の in front of だろう/でしょう? Is のだろう used
when the speaker wonders about something to himself?

For example, what would be the translation of these sentences:

> 日本は、これからますます高齢化が進むだろう。  
>  It seems that lately the aging in Japan is increasing.
>
> 最近、デパートの売り上げが伸びている。景気が回復しているのだろう。  
>  Store's sales increased. I wonder if the business is recovering?
>
> 何をするのだろうか。  
>  What could I do?
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2013-12-31T18:33:27.333
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2016-02-07T08:24:33.990
2020-06-17T08:18:27.500
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question
grammar particles particle-の questions
Meaning of のだろう?
When a verb is directly marked by だろう／でしょう, there are three meanings:

> 行くだろう  
>  "It will (probably) go." (downwards tone throughout)  
>  "It's going, isn't it?" (upwards during 行く, then downstep)  
>  "I wonder if it will go." (neutral tone throughout)

While if it's marked by （ん／の）＋（だろう／でしょう）, it's like before, but the first
option is strengthened a little:

> 行くのだろう  
>  "I'm sure it will go." (downwards tone throughout)  
>  "It's going, isn't it?" (upwards during 行くの, then downstep)  
>  "I wonder if it it will go." (neutral tone throughout)

In writing, when there isn't a の, the 3rd option (rhetorical question) isn't
quite as likely, but in speech they are all disambiguated quite well. I'm not
sure if that's a personal quirk of my Japanese or not.
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2013-12-31T23:59:57.560
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2013-12-31T23:59:57.560
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answer