How to ask a question with だろう in the correct way? Should I add か in the end?

Like 何だろうか?
I saw a lot of examples and almost always guys omit か in the end. And just say 何だろう;いつだろう。。。


~だろう forms a question that is mainly addressed to yourself. It's like "I wonder". If you are clearly requesting an answer from someone else, don't use it.

Next, か after だろう in a yes/no type question corresponds to English "whether/if", and it's mandatory. か in a wh-question (i.e., a question including いつ, だれ, 何, なぜ, etc) is purely optional, but is usually omitted especially in casual speech.

  • 彼は来るだろう? I wonder if he will come.
  • これは食べられるだろう? I wonder if I can eat this.
  • これは何だろう? (I wonder,) What's this?
  • これは何だろうか? (I wonder,) What's this?
  • どうしてだろう? I wonder why.
  • どうしてだろうか? I wonder why.


  • thanks a lot for so detailed explanation!
    – Max
    Sep 25 '19 at 1:53

I think that generally you would only need/put the か in formal form such as ...ですか or ...ますか. In casual speaking the か is rarely used at the end as you just use intonation to make it a question.

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