Grammar Info
N4 Lesson 7: 9/18

のだろうか
I wonder...

Versions without ん/の are also acceptable but sound old-fashioned

Structure
Casual
Formal
Verb +((1))+ だろう
[い]Adjective +((1))+ だろう
[な]Adjective +( + (1))+ だろう
Noun +( + (1))+ だろう

(1)
Verb +((1))+ でしょう
[い]Adjective +((1))+ でしょう
[な]Adjective +( + (1))+ でしょう
Noun +( + (1))+ でしょう

(1)
Details
Register Standard
使用域 一般
Information
When using だろう (the conjugated auxiliary verb) is grouped with (the question particle), it presents the statement before it as something that the speaker is unsure about. In this way, it sounds similar to ‘I wonder if (A)’ in English.
To use this construction, the statement before だろうか must be nominalized (turned into a noun-phrase). This is done through the use of , or なの (in the case of な-Adjectives and nouns.
  • 私(わたし)たちチーム勝(か)てるのだろうか
    I wonder if your team can win.
  • 彼女(かのじょ)本当(ほんとう)に彼氏(かれし)が欲(ほ)しいのだろうか
    I wonder if she actually wants a boyfriend.
  • あの人(ひと)大丈夫(だいじょうぶ)なのだろうか
    I wonder if that person is okay.
  • あれ本当(ほんとう)に食(た)べ物(もの)なのだろうか
    I wonder if that is really food.
Despite the grammatical rule relating to nominalization using (or なの), this part of the phrase is often omitted.
  • トム私(わたし)誘(さそ)うだろうか
    I wonder if Tom will invite me. ( omitted)
  • あの人(ひと)本当(ほんとう)に弁護士(べんごし)だろうか
    I wonder if that person is actually a lawyer. (なの omitted)
だろうか is quite masculine, so in order to sound more polite/ladylike, でしょうか may also be used instead.
  • そんな高(たか)鉛筆(えんぴつ)トム買(か)のでしょうか
    I wonder if Tom will buy a pencil that expensive.
  • あの車(くるま)キム車(くるま)なのでしょうか
    I wonder if that car belongs to Kim.
Caution
Although だろうか is quite masculine, it does not strictly mean that でしょうか is feminine. でしょうか may be used confidently by either women or men.
Fun Fact
Like だろう, だろうか may be used to ask a question, or simply to express the speaker's inner thoughts.
  • この人(ひと)言(い)っていること本当(ほんとう)なのだろうか
    I wonder if what this person is saying is true. (Said while talking to oneself)
  • そこに息子(むすこ)連(つ)れて行(い)っていいのだろうか
    I wonder if I can take my son there. (Said while talking to oneself)
However, だろうか is most commonly used to express a personal ‘I wonder’, in a similar way to かな. Because of this, even if it is used as a question, the listener may assume that you are not specifically looking for an answer from them.
Slow Male
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彼(かれ)都合(つごう)悪(わる)い(の)だろうか
I wonder if it is bad timing for him?
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もうすぐ時間(じかん)だろうか
I wonder if it is about time.
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練習(れんしゅう)たらうまくなる(の)だろうか
I wonder if I will get better at it if I practice.
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