would do, would have done

[joham]

The following sentences come from MACMILLAN, and my questions are in the brackets:
1. It's no use talking to Henry--he wouldn't understand. (Can we use won't instead? Why?)
2. Where would he have hidden the keys? (Is there any difference if we say 'Where did he hide the keys?'?)
3. --Sylvia said it was your fault.
--Well, Sylvia would say that, wouldn't she? (Can we say 'Sylvia will always say that, won't she?' without changing the meaning? When criticizing someone's typical behaviour for a particular action, do we always use 'would' rather than 'will'?)

Thank you very much in advance.

 

[riverkid]

The following sentences come from MACMILLAN, and my questions are in the brackets:
1. It's no use talking to Henry--he wouldn't understand. (Can we use won't instead? Why?)

Yes, you can. Kind of means "don't even bother because if we were to ask him ...".

2. Where would he have hidden the keys? (Is there any difference if we say 'Where did he hide the keys?'?)

'would' is more speculative, asking for suggestions. 'did' kinda ask the question, as if the person ought to know.

3. --Sylvia said it was your fault.
--Well, Sylvia would say that, wouldn't she? (Can we say 'Sylvia will always say that, won't she?' without changing the meaning? When criticizing someone's typical behaviour for a particular action, do we always use 'would' rather than 'will'?)

Thank you very much in advance.

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