Which one is correct?
"Any letter"
"Any letters"
Let me provide the context: "Are there any letters in the post box?"
Which one is correct?
"Any letter"
"Any letters"
Let me provide the context: "Are there any letters in the post box?"
"Any is normally used with plural and uncountable nouns in questions, negative and conditional sentences. We would normally require a/an before a singular countable noun. However, when we want to emphasise that any means of any kind, it is quite natural to use any with singular uncountable nouns." This has been nicely explained in detail at http://www.bbc.co.uk/worldservice/learningenglish/grammar/learnit/learnitv303.shtml
Can you please use it in a sentence? Rand is right, both are correct... though in certain contexts I can see how one might be less appropriate or might contradict the intended meaning of what you're trying to say.
We use "any letters" when we mean "one or more" and we use "any letter" when we mean "it doesn't matter which one."