だろう

だろう
auxiliary
probably, I wonder, right?
grammatical
1. probably, I think, I suppose
Expresses conjecture or supposition about something uncertain.
誰(だれ)からだろう。
I wonder who it's from.
明日(あした)は晴(は)れるだろう。
It will probably be sunny tomorrow.
彼(かれ)も来(く)るだろう。
He'll probably come too.
2. right?, isn't it?
Seeks confirmation or agreement from the listener (often with rising intonation).
そうだろう？
Right? Isn't that so?
面白(おもしろ)かっただろう？
It was interesting, wasn't it?

だろう is the volitional form of the copula だ used to express conjecture.

Forms

  • Plain form + だろう
  • Noun/na-adjective + だろう (no だ before)
  • i-adjective + だろう

Keigo

  • でしょう is the polite equivalent
  • 〜だろう (plain) → 〜でしょう (polite)

Common patterns

  • Statement + だろう = conjecture (probably)
  • Question word + だろう = wondering (I wonder...)
  • Statement + だろう？(rising) = seeking confirmation (right?)

Similar words

  • だろう: Conjecture based on reasoning or assumption
  • かもしれない: Possibility, "might be"
  • はずだ: Expectation based on evidence, "should be"

Gender note

  • だろう can sound somewhat masculine in casual speech
  • でしょう is more neutral and commonly used by all speakers

Related Words

Related: 違(ちが)いない (stronger certainty)
Keigo: でしょう (polite)
Compare: かもしれない (Possibility, "might be")
Compare: はずだ (Expectation based on evidence, "should…)
general
Added 2026.2.3 10:40 · Revised 2026.9.2 13:01
09500/09576_darou