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> 今日何を食べたいですか  
> What do you want to eat today?

In other words, what would happen if I say:

> 今日何は食べたいですか ?
>
> 今日何が食べたいですか ?

(I want to know the rough meaning of the sentence even if the sentence is
wrong.)
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2018-05-17T12:11:07.113
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2018-05-17T14:14:08.310
2020-06-17T08:18:27.500
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question
particles syntax
What would happen if I use は or が in 今日何を食べたいですか?
While both 「は」 and 「が」 as particles are "subject indicators" (please take note
that I am not sure of the actual linguistic term for this), they emphasise
different things.

「は」places emphasis on what comes **after** it, ergo:

> 今【いま】はいいかんじです。
>
> (I feel) _good_ now.
>
> 今日【きょう】は疲【つか】れます。
>
> (I) am _tired_ today.

In your hypothetical example, you'd be placing emphasis on 「食べたい」, as in "What
do you want to _eat_?" It feels like asking if you _want to eat "what"_.

As ericfromabeno states (along with Chocolate's very helpful answer), using
「は」for this kind of statement is unnatural. I think 「を」is still more
appropriate particle to use in this sentence.

「が」places emphasis on what comes **before** it, ergo:

> チョコレートが好【す】きです。
>
> "I like _chocolate_."
>
> 気分【きぶん】が悪【わる】いです。
>
> "I _feel_ bad."

Your hypothetical example places the emphasis on 「何」, as in " _What_ do you
want to eat?"
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2018-05-17T12:45:21.957
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answer
You can say...

> 今日は何 **を** 食べたいですか？  
>  今日は何 **が** 食べたいですか？

を is the object marker. You can use が here instead, since が can mark the
object of the ～たい form verb.

Your second sentence:

> 今日何 **は** 食べたいですか？

would be incorrect. You don't use the topic/contrastive は for a question word.  
◎「何が～～？」 ◎「誰が～～？」 ◎「いつ(が)～～？」etc.  
×「何は～～？」 ×「誰は～～？」 ×「いつは～～？」 etc.

As you know, は is basically the topical/thematic particle (主題の「は」) or the
contrastive particle (対比の「は」), and can replace が, を. But it can't be attached
to the question word 何、どこ、誰、いつ etc... (cos 何、どこ etc. can't be a topic/theme of
a sentence, nor can they be contrasted with some other element of the
sentence.)
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2018-05-17T13:14:58.707
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answer