I've read that が is the particle used when asking a question, but then I see sentences like 一番好きな本はなんですか or 一番いい先生はだれですか.

Is there a reason why が is not used in this type of sentence, or is the rule re: が in a question sentence just a vague guideline?

1 Answer 1


I think you have misunderstood the advice you were given. It is not true that が must be used in questions or that は cannot be. But because interrogative words like なに, だれ, etc. refer to undefined objects, it does not make sense to use the topic particle は with them. So if they are the subject of the sentence, then they must be marked with が rather than は. I believe this is all they were trying to get at.

For example:

× だれ電球を発明したの。
○ だれ電球を発明したの。

The question can, however, be rephrased as


without any problem.

  • 2
    I think it may help if you could you comment on 一番いい先生だれですか? Is that grammatical (I don't think so), but if so, in what scenario could it be used? Thanks. Commented Jan 27, 2019 at 17:43

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