のだろうかI wonder...

When だろう (the conjugated auxiliary verb) is grouped with か (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 の, or なの (in the case of な-Adjectives and nouns).

• 私(わたし)たちのチームは勝(か)てるのだろうか。

  I wonder if our team can win.
• 彼女(かのじょ)は本当(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)は大丈夫(だいじょうぶ)なのだろうか。

  I wonder if that person is okay.
• あれは本当(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 の (or なの), this part of the phrase is often omitted.

• トムは私(わたし)を誘(さそ)うだろうか。

  I wonder if Tom will invite me. (の omitted)
• あの人(ひと)は本当(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)い鉛筆(えんぴつ)をトムが買(か)うのでしょうか。

  I wonder if Tom will buy a pencil that expensive.
• あの車(くるま)はキムの車(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)が言(い)っていることは本当(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)を連(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.