modality N4 common casualwritten
〜のだろうか — I wonder if ~
〜のだろうか ・ のだろうか
Builds on だろう
Meaning
- I wonder if ~ / could it be that ~? — explanatory の + conjectural だろう + question か: a weighed, often introspective doubt
のだろうか layers three pieces: の frames the matter as the thing in question, だろう adds conjecture, か makes it a question turned over in the mind. The result is heavier and more reflective than かな — it suits writing and serious pondering ('I wonder whether this is really right'). The polite form is のでしょうか; casual speech often drops to んだろうか.
Key sentence
本当にこれでいいのだろうか。
I wonder if this is really all right.
Formation
| Attaches to | Form | Example |
|---|---|---|
| Plain form + のだろうか (noun・na-adj take な before の) | … plain + のだろうか / Nなのだろうか | 正しいのだろうか / 必要なのだろうか |
Examples
なぜ彼はあんなことを言ったのだろうか。
I wonder why he said something like that.
人類はどこへ向かっているのだろうか。
Where is humanity heading, one wonders?
この選択は正しかったのだろうか。
Was this choice really the right one, I wonder.
Easily confused with
〜かな Both wonder, but かな is light, casual musing; のだろうか is heavier and more introspective/written — a doubt you genuinely weigh, not a passing 'hmm'. だろう Plain だろう conjectures ('probably ~'); adding のか turns the conjecture into a question you put to yourself ('I wonder whether ~'), with の framing the issue as the point in doubt.
Notes
- Without の — 〜だろうか — also means 'I wonder', but のだろうか specifically frames the doubt as being about the underlying situation/explanation, which is why it feels more deliberative.
See 〜のだろうか in real sentences
Jengo shows 〜のだろうか the way you actually meet it: inside real Japanese sentences, so it sticks instead of staying an abstract rule.
Study it in Jengo