The rules I know:
0 count of item : "zero items plural
1 count of item : "one item" singular
greater than 1 count of item : "many items" plural
less than 0 count of item (as in mathematics) : "negative one item / negative x items"
This leads me to believe that it's proper to use plural form in any situation where the count is not exactly 1.
Jonny has (unknown amount of) apple - (to me this is wrong)
Jonny has (unknown amount of) apples - (to me this is correct)
If Jonny has (unknown amount of) apples, is it then acceptable to say:
Jonny has apples - (I think so, and there are many examples of this in English; however it occurs to me that Jonny may have 0 apples and therefore you wouldn't say 'Jonny has apples' but rather 'Jonny has no apples' or 'Jonny does not have any apples')
Is there any situation in where this is not the case? For example if:
I know that Jonny has 0 apples and I give him 1 apple.
Jonny now has 1 apple.
But if I don't know how many apples Jonny has and I give him 1 apple.
Would I still say that
Jonny has 1 (an) apple? or is it acceptable to say
Jonny has apples because I don't actually know for certain how many apples Jonny has?