Use of あったら with たい form


Reading through a list of questions on a small questionnaire that came with a
Japanese textbook, I found the following:

> どんな本があったら買いたいと思いますか？

I am puzzled by the combination of the conditional of ある with かいたい.

> どんな本が買いたいと思いますか？

Clearly means "what kind of book would you like to buy?". Normally I would
expect an あったら to split the sentence into two clauses, but that would split
どんな from 買いたい. What, grammatically is going on here?




I think the Q&A @user3856370 has pointed you to should sufficiently answer
your question. I'd like to say a few words about how I personally understand
that sentence. Here goes nothing:

Very often you see Japanese verbs used unaccompanied by a subject or an
object, or both. See [this
answer](https://japanese.stackexchange.com/a/84453/30454) for a more detailed
explanation on this.

> どんな本が買いたいと思いますか？

Your proposed version dispenses with the あったら conditional and has the patient
of the verb どんな本 as the subject of the sentence. It is thus a single-clause
sentence with どんな本 as its subject. Let's look at the original sentence:

> どんな本があったら買いたいと思いますか？

You are right that あったら often marks a clause. In the original sentence,
although there is no 読点 (comma), 「どんな本があったら」is 主節の述語を修飾する副詞節 (an adverbial
clause that modifies the predicate of the main clause), because it describes a
condition that, when met, leads to the next step (thinking about buying them).

If we put back in the sentence things that are omitted:

> どんな本があったら、 **それを/が** 買いたいと思いますか？

> What kinds of books, if the store has them, would you like to buy?

Since either が and を can be used here, it doesn't really matter if you regard
the pronoun それ, a placeholder for どんな本, as a syntactic subject or object.
Semantically of course, it is the object/patient of the verb 買う.




I think the Q&A @user3856370 has pointed you to should sufficiently answer
your question. I'd like to say a few words about how I personally understand
that sentence. Here goes nothing:

Very often you see Japanese verbs used unaccompanied by a subject or an
object, or both. See [this
answer](https://japanese.stackexchange.com/a/84453/30454) for a more detailed
explanation on this.

> どんな本が買いたいと思いますか？

Your proposed version dispenses with the あったら conditional and has the patient
of the verb どんな本 as the subject of the sentence. It is thus a single-clause
sentence with どんな本 as its subject. Let's look at the original sentence:

> どんな本があったら買いたいと思いますか？

You are right that あったら often marks a clause. In the original sentence,
although there is no 読点 (comma), 「どんな本があったら」is 主節の述語を修飾する副詞節 (an adverbial
clause that modifies the predicate of the main clause), because it describes a
condition that, when met, leads to the next step (thinking about buying them).

If we put back in the sentence things that are omitted:

> どんな本があったら、 **それを/が** 買いたいと思いますか？

> What kinds of books, if the store has them, would you like to buy?

Since either が and を can be used here, it doesn't really matter if you regard
the pronoun それ, a placeholder for どんな本, as a syntactic subject or object.
Semantically of course, it is the object/patient of the verb 買う.

