# いつだか



## xuliang

いつ*だか*まだわからない。

The above is an example sentence in a Japanese-Chinese dictionary. It says it means "It's still unknown when". I don't quite understand the part in bold. What function is it there?

Thank you.


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## Flaminius

Your sentence is an indirect question sentence for which a _Wh_-sentence is embedded as the object of わかる (> わからない).  Da is the verb of the _Wh_-sentence and _ka_ is the complementiser.

Consider the following theoretical procedure as a help to understand the embedding.
1. The original declarative sentence with the coular _da_ as the verb.
締切は明日だ
2. The subject is ellipted.
明日だ
3. 明日 is replaced by the _Wh_-expression of time.
いつだ
4. The sentence takes ka and embedded into the matrix sentence.
いつだかわからない


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## xuliang

Hi, Flaminius, many thanks for your very detailed answer. The whole structure of the sentence is clear to me now. I just have a question about "か". If it's ”が” I would understand it. I don't understand why it's  ”が, rather than ”が". Thank you.

いつだ*か*わからない


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## Flaminius

If you know _ka_ is the sentential particle that marks a question sentence, I would say that it is mandatory in indirect questions.

It works as a complememtiser too. The question sentence, wheather it is a Yes/No question or a Wh-question, can take a case particle by way of _ka_.  It is perfectly grammatical to say:
Itsu da ka ga wakaranai.

You can omit _ga_ but never _ka_ for an embedded question sentence. [Embedding is to make a sentence like one of part of speech (e.g., a noun) and include it in another sentence.]


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## SoLaTiDoberman

いつ*だ*かまだわからない I don't know whether when *it is*.
＝いつ*である*かまだわからない I don't know whether when* it is*.
＝いつかまだわからない I don't know whether when.

か＝whether

The English shown is wrong, English-grammatically speaking. But I intentionally wrote it in order to show the function of か.


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## xuliang

Flaminius said:


> If you know _ka_ is the sentential particle that marks a question sentence, I would say that it is mandatory in indirect questions.
> 
> It works as a complememtiser too. The question sentence, wheather it is a Yes/No question or a Wh-question, can take a case particle by way of _ka_.  It is perfectly grammatical to say:
> Itsu da ka ga wakaranai.
> 
> *You can omit ga but never ka for an embedded question sentence. *[Embedding is to make a sentence like one of part of speech (e.g., a noun) and include it in another sentence.]


Hi, Flaminius, Sola, thank you for your very helpful answers. 

After reading, I want to confirm, are the three sentences below correct? If they are correct, do they mean the same? Thank you.
いつだ*か*まだわからない .
いつだ*が*まだわからない 
いつだ*かが*まだわからない


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## Flaminius

いつだ*か*まだわからない
--Most common construction, unmarked sentence

いつだ*が*まだわからない 
--incorrect

いつだ*かが*まだわからない
--Less common because it emphasizes "when" and make you sound, "I know all info but time."


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## karlalou

xuliang said:


> If it's ”が” I would understand it. I don't understand why it's ”が, rather than ”が".


*がわからない* is used as それがわからない, こたえがわからない, よみかたがわからない, etc. In other words, we consider the one in front of がわからない as the _object _of わからない (Actually I'd say it's more the 'theme' of わからない than the object).

But when it's with an interrogative like いつ, or どれ, or なん(なに) we want it to be with か.

か adds the sense of _uncertainty_ that it's more natural for us if it's いつかわからない, but this still feels incomplete.

Adding だ to this makes it feel like a standard sentence: いつだかわからない.
It's not much to do with logic, but we just say it in this way.
I never think of it, but now I see that it can be said that there's それは implied, それはいつだかわからない, and it becomes a subordinate clause.

We also say どれだかわからない, なんだかわからない, だれだかわからない, or どうだかわからない.


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## xuliang

karlalou said:


> *がわからない* is used as それがわからない, こたえがわからない, よみかたがわからない, etc. In other words, we consider the one in front of がわからない as the _object _of わからない (Actually I'd say it's more the 'theme' of わからない than the object).
> 
> But when it's with an interrogative like いつ, or どれ, or なん(なに) we want it to be with か.
> 
> か adds the sense of _uncertainty_ that it's more natural for us if it's いつかわからない, but this still feels incomplete.
> 
> Adding だ to this makes it feel like a standard sentence: いつだかわからない.
> It's not much to do with logic, but we just say it in this way.
> I never think of it, but now I see that it can be said that there's それは implied, それはいつだかわからない, and it becomes a subordinate clause.
> 
> We also say どれだかわからない, なんだかわからない, だれだかわからない, or どうだかわからない.


Flaminius, Karlalou, many thanks to you both for the additional information; very helpful.


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