Using は before 欲しい instead が

Question

I was doing some exercises and the book that I'm using translated:

I don't want shoes

to

靴は欲しくないです

I answered using が particle instead は, since, as far as I know, I should use が before 欲しい. So why did the book use は this time?

I imagined that the reason is to make a contrast/comparison that は provide. Is that why?

Answer 1

"I want xxx." vs. "I do not want xxx."

When you want something, you will generally say:

「XXX + が + ほしい」

and when you do not want something, you will generally say:

「XXX + は + ほしくない」

The only times you can and must use 「XXX + が + ほしくない」 is when it is used in the if-clause or relative clause. Thus, it is correct to say:

Relative Clause:「靴{くつ} + が + 欲{ほ}しくない人は靴屋{くつや}へは行かない。」

"A person who does not want shoes would not go to a shoestore."

If-Clause:「靴 + が + 欲しくなければ、なんで靴屋に来たの？」

"If you do not want shoes, why did you come to a shoestore?"

Moving on...

The contrastive 「は」

This is essentially a different topic from what has been discussed above.

It is correct to say:

「靴 + は + 欲しくない。」

when you do not want shoes but want another thing. Thus, you can say:

「靴は欲しくないけど、ジーンズは欲しい。」

That is a pair of contrastive は's. "I don't want shoes, but I want some jeans."

I imagined that the reason is to make a contrast/comparison that は provides. Is that why?

No, as I stated above. We are talking about two different things. One is affirmative vs. negative. The other is contrastive.

Answer 2

He may be asked “what do you want as a present?” or “ do you want shoes as a present?”
Then he uses は containing contrast/comparison meaning.
He wants something but shoes.

靴は欲しいです。
I want shoes. (He wants other things too.)
靴が欲しいです。
I want shoes. (He doesn’t want other things.)
靴が欲しくないです。
I don’t want shoes.(He’ll accept anything but shoes.)
靴は欲しくないです。
I don’t want shoes.(He’ll refuse something besides shoes.)

Answer 3

As to the question of when to use はほしい　[はほしい　and not ほしくない]:

I think that @l'électeur gave one good example (=when emphasizing the contrast of what one wants and what not) with the example 「靴は欲しくないけど、ジーンズは欲しい。」

IF YOU READ FURTHER [NOT ADVISABLE, BUT I DON'T DELETE THIS

1. Due to the valuable comments

2. To indicate when は欲しい IS NOT USED ;-)

3. To call for additional case where は欲しい　(and not e.g. が欲しい or は欲しくない)　is used

]

In addition I can think of at least two other situations to use は but at least I clicked on this question to find out more, so I hope the natives / gurus [also others than @l'électeur ] correct / add:

Can be used like in a [phrase or at least close] "あれはほしいこれはほしい" as a critical statement about someone with too many requests [and here it is more about requests than aspirations], i.e. in a stereotypical case two employees could talk about their boss [or similarly 2 managers could talk about someone's difficult team member] who is never satisfied and comes up with continues and unreasonable requests.

Can be used when the target of the aspirations is a bit abstract and/or not immediately achievable / obtainable, like I want that kind of life [ああ言う人生はほしい]