When do we use 'a/an' and when 'any' in questions?

[Minhthu]

1. Do you have a child?

2. Do you have any child?

3. Do you have any children?

4. There isn't a hospital in our town.

5. There isn't any hospital in our town.

6. There aren't any hospitals in our town.

I know #2 is incorrect. Please could you explain to me how '' any '' and '' a '' depend on the context?
If possible , give me some examples.

Thank you very much for your reply.

[Mister Micawber]

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#2 is fine if any is stressed, though it is less common than any with a plural or uncountable noun.
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Native English teacher at Mister Micawber's

[Alan]

Hi minhthu,

I would suggest in your sentence (2) you need some kind of definition so that you isolate the noun child as in:

Do you have any child living at home?

Do you have any child between the ages of 5 and 13?

Alan
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English as a Second Language
You can read my ESL story Phrasal Verbs/run

[Chocolatee]

"A" connotes an absolute singularity. If you say "a child", it means one child. When you say "any child", the number is not certain. The number could range from zero to any number.