作为限定词，any既可以表示任何一个人或物（此时后接单数名词），也可以表示大于零的不确定的数或量（此时后接复数或不可数名词）。前者可用于各种句子，但用于肯定句时通常为非肯定语境（例如句子含有表示可能或推测的形容词，不定式表示的未必发生的动作，将来可能发生的动作等。不可用于过去已经确切发生的情景）。后者则通常用于否定句、疑问句和条件句。

具体可参读《韦氏高阶》的释义和例句：

always used before a noun

1 

— used to indicate a person or thing that is not particular or specific

• Ask any man you meet, and he will tell you the same thing.

• Any one of them could have answered the question.

• You can return the product if any defect appears within the first six months.

• Any plan (at all) is better than no plan.

• Any [=every] child knows that. [=all children know that]

• He is as good as any other pitcher in the league.

• We can meet any day but Monday.

• You could have seen him any afternoon last week.

• The recipe uses a large amount of pepper, and not just anypepper, but a special blend imported from India.

• You have to be a member to go there. They won't let just any person in.

2 

— used to indicate an amount greater than zero or none — usually used in negative statements, in questions, and in statements with if or whether

• You haven't eaten any salad. [=no salad has been eaten]

• I can't find any stamps.

• Don't pay any attention to him.

• There is hardly any difference between the two teams.

• They dropped by without any warning.

• We don't want there to be any misunderstandings.

• The company has denied any [=all] responsibility for the accident.

• There are few if any [=few or no] details about the accident.

• Do you have any money?

• He asked if/whether you had any money.

• If there are any errors, report them to me. = Report anyerrors to me.

• If you can give me any help, I'd appreciate it. = I'd appreciate any help you can give me.