Can anybody explain why かい is used in the following sentence from 第三夜 (Dream #3 - from Natsume Sōseki's Ten Nights of Dreams, 夢十夜):


"I asked [him] when [he] had gone blind to which [his] casual reply was "Oh, ages back".

According to the Dictionary of Basic Japanese Grammar and the answer to a previous question, linked below, かい is for yes/no questions, だい is for WH-questions.

In what situation can I use ~かい (for interrogative question)?

  • 2
    Nevermind that old thread. It is another case of an incorrect answer selected as best. Nothing new at SE. Native speakers use かい with WH-questions ALL THE TIME. See cache.yahoofs.jp/search/…
    – user4032
    Commented Feb 4, 2014 at 3:53
  • 1
    I looked up かい in 明鏡 and it had this example which contains だれ: 「そんなことだれがやるかい」 On the other hand, the grammar book you cite gives the following examples as ungrammatical because they aren't yes-no questions: 「どこへ行く(の)かい。」「あの人はだれ(なの)かい。」 And in this comment, Matt wonders aloud whether the difference might be 'subtler than "yes/no vs open-ended"'. I suppose it would be helpful to hear more about the difference かい versus だい from someone knowledgeable.
    – user1478
    Commented Feb 4, 2014 at 5:10
  • @TN: Thank you. I am glad to know I was not imagining all those WH-かい questions but I am still not clear from your very useful link: From Q8, it seems the missing nuance is that WH-questions take のかい/なのかい but not かい (and incidentally, だい can only be used in a WH-question) ..However this contradicts the guidance: 「疑問詞のあとに言葉が入るとき疑問詞+〜+のかい(かい)」を使う。which suggests ~かい is also a good answer for Q8. Have I missed something?
    – Tim
    Commented Feb 4, 2014 at 7:03
  • 1
    Related: japanese.stackexchange.com/questions/15723/…
    – Szymon
    Commented May 19, 2014 at 20:57

2 Answers 2


We spent a while talking about this on chat tonight, and I think I understand a little better now thanks to Chocolate and Yang Muye. So I'm going to try to write up the conclusions I came to in an answer.

Rules for だい and かい

I think the description given in the grammar dictionaries is fairly accurate for today's Japanese, but it may be a bit of a simplification, and is perhaps not 100% descriptively accurate. After all, we know from 非回答者's comment and from the fact that 夏目漱石 wrote it that かい must be possible! The only question is how we should make sense of it.

To get started, I read the rules on the page 非回答者 linked to and went through the quiz at the bottom, and I discovered something very interesting:

I can get 100% of the answers right with two simple rules!

  Rule 1. If you can't use だ, you can't use だい.

  Rule 2. If you can't use か, you can't use かい.

That is, I ignored the presence of い entirely and focused on whether だ, か, or の was grammatically possible. In all cases I ended up with the right answers. You'll note that the quiz never makes you decide between だい and かい when both だ and か are possible.

And although these rules aren't quite adequate on their own, they seem natural enough if you think of い as a separate particle. In fact, dictionaries list い as a sentence-final particle. That leads us to rule #3:

  Rule 3. The particle い is unambiguously clause-final.

What does this mean? Compare the following examples:

A. 会議はいつ
B. 会議はいつかい

The first example sounds incomplete—you could complete it by adding something to the end, like 会議はいつか、知ってますか?. But because the second example ends with い, a sentence-final particle, it seems like a complete sentence. So this is one place that かい is possible that か would seem strange.

So this is a slight revision to our rules #1 and #2, which otherwise serve us quite well. Now, let's move on to the last two rules:

  Rule 4. When there's no question word, you can't use だい.

  Rule 5. When there is a question word, you usually use だい.

That is to say, だい is more common in today's Japanese than かい with a question word. And while かい is still possible today, I think it's a less common than だい when both are possible, and in some cases it might seem a little bit old-fashioned sounding. Chocolate reported in chat that it was the sort of thing you might find in a 夏目漱石 novel, and of course that's exactly what your question is about.

So I think that Makino et al. probably simplified things slightly in their grammar dictionaries. Because it's more common to use だい than かい today, their rules work fairly well most of the time, but they might not have 100% descriptive adequacy.

An explanation?

I've come up with an explanation for why this the case. It's a bit of a just-so story, so I wouldn't put too much stock in it, but helps everything make sense in my head, so I thought I'd include it here:

  1. I think 誰だい is possible for the same reason you can say 誰だ—the presence of the question word 誰 makes it obvious that you're asking a question, even with だ and without an overt marker like か or rising intonation. That doesn't force you to use だい, but it makes it possible, and practically speaking it's more common to use だい than かい when both are possible syntactically.

  2. On the other hand, a sentence like おいしいのだい fails as a question for the same reason おいしいのだ does. Without a question word, you need another way to signal to the listener that you're asking a question, and that most likely means using rising intonation or an overt question particle. This rules out だ and therefore だい as well, as they would be taken as signals that you're not asking a question.

Of course, I never use だい or かい in my own speech so these rules are somewhat academic for me :-) But I hope either the rules or the reasoning help you understand why it was okay that he used かい in his writing.

  • 1
    It seems to hold but am I right in thinking that for question 8 of the quiz, かい is also correct but の is more natural (and therefore の is the correct answer)? [The answer to my question, in the comment above, seems to be either (1) that (な)のかい is more natural than かい but it is not necessarily wrong. (2) There is misprint.]
    – Tim
    Commented May 25, 2014 at 3:30
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    @Tim For question 8, I didn't really think it was about い, but really just a question of whether you should include の. I'm not sure I can say か or かい alone is actually wrong, but I think using の would be more common / more natural there (whether you add a following か or not).
    – user1478
    Commented May 25, 2014 at 4:02
  • I sent a question to the address on the website: The use of の with かいandだい is the same as with のですか:depends on the nature of the question and not the question marker itself (ie it is used when emotional emphasis is required), and this is why in some of the examples (かい)is not given as an example.
    – Tim
    Commented May 29, 2014 at 3:24
  • Note on entry in Dictionary of Basic Japanese Grammar: Based on the information here it would be more accurate to say: The grammatical use of だい and かいto end questions follows the use of だand か: だい is only really used with questions containing WH-words, かい can be used to end questions with or without a WH-word although the latter is more old fashioned (and hence less common).
    – Tim
    Commented May 29, 2014 at 3:37

The way I learned it is that ~かい actually consists of two particles. The question particle ~か and the final interjection particle ~い. See here for a very brief description. In contemporary Japanese, this particle appears in contexts of familiarity, where speaker and hearer are well acquainted. The particle can also follow ~ぞ, making it ~ぞい. Here's the first example from a search for ぞい on Yahoo Japan.


And the expression ~だい as in 何だい? also contains the particle ~い. If you want to use these expressions, carefully select the context. Asking your Japanese boss


will not make you last long in the company.

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