One of my textbooks said that you cannot use the particle は with 何 and undefined words of the こそあど.

Yet I'm sure I've heard これは何ですか。 many times before, and これが何ですか。 sounds unnatural to me.

What is the correct usage?

  • 4
    It means you can't say 何はおかしい or どれは好き, not that you can't say これは何ですか or 君はどれにする.
    – Angelos
    May 5, 2016 at 11:10
  • I had forgotten to mention that the set phrase 何はともあれ 'in any case' has は after 何, but that's the only exception I can think of.
    – Angelos
    May 5, 2016 at 16:56
  • 1
    @Nothingatall There are other exceptions, but they're rather uncommon. It's still possible to productively attach は to a wh-phrase under certain circumstances. I have a bunch of examples saved, like 「 誰はもらって誰はもらわないというのはよくない」「兄さん、じゃもう一つ聞きたいんですがね、人間は誰でも、他人を見て、 誰は生きる資格があって、誰は資格がない、 などとそれを決める権利を持ってるものでしょうか?」 But these exceptions are probably irrelevant to people learning the basics, so if we want to discuss them we should probably do so in a separate question.
    – user1478
    May 5, 2016 at 18:40
  • 1
    「これが何ですか」 is kind of an exception, I think, althogh at exam, it would be greatly dealt as "wrong". But when someone is asking another ( especially in anger ), it would mean So what's the problem with this according to you!
    – user7644
    May 5, 2016 at 23:52

2 Answers 2


The key word is "undefined". は is a topic marker, and you can't switch topics to something you don't know about yet.

In 「これは何ですか?」, は is acceptable because これ is a specific, definite thing (at least in context) and 何 is about asking for more information about that thing.

In「何が好きですか?」. the 何 isn't "definite" to the speaker because it is a "placeholder for anything" 何. Of course, 好き puts an additional constraint on it, and if you re-arrange the sentence, you can say 「好きなものは何ですか」 because 好きなもの is definite enough to switch topics to with は.

On a side note, が is the subject marker. Every complete phrase must have a subject, so you might wonder why sometimes there isn't a が. Sometimes it is because the subject is implicit... but sometimes it is because the subject is the same as the topic.

For example, in 「私はアメリカ人です」, 私 is both the topic and the subject. That is, the actual meaning is (note: this is not correct Japanese for basic subject-marking use of が!) 「私はがアメリカ人です」. But Japanese has a forced grammatical convention where the は and が particles collapse to just は when the same noun is being marked as both subject and topic (except in certain other special usages of が). In other words, が MUST be abbreviated out in these cases. This is consistent with the view presented on p.118 of "A Dictionary Of Basic Japanese Grammar".

  • 私は私がアメリカ人です is different from 私はアメリカ人です and the latter is not abbreviation from the former, because が is not a marker that straightforwardly stands for the subject in a sentence though it can in a clause. For example, 私は私が食べます implies a situation when you are asked what you do if you find expired foods in the fridge and you reply that you'd eat it yourself instead of other family member.
    – user4092
    Jun 5, 2016 at 11:09
  • There are certainly other usages of が (eg contrastive が), and because of the "collapse" rule I mentioned, an actual grammatical usage going against the rule stand out as either being a different usage or exceptional in some way. This is why I marked it as "(note: not correct Japanese)" (I meant specifically for basic subject-mark usage only), but I can certainly see how it might be confusing. I'll try to clean that up a little, thanks for the feedback. Jun 5, 2016 at 11:22
  • I can see what you are getting at. Up vote.
    – KyloRen
    Jun 5, 2016 at 12:08

In most cases, が is used before a question word (何、どれ、etc.) as opposed to は. This is because が has the nuance that it emphasizes this word which is the same reason が is usually used when answering a question (ex: "誰がやったの?" => "先生がやったよ")

Depending on the nuance trying to be conveyed, が or は can be used naturally after any non-question こそあど words.

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