Singular countable nouns after "there isn't any"

Question

Can I ever use singular countable nouns after there isn't any? I have read many books that say any can be used with both singular and plural countable nouns. Though plural nouns is more more common in negative sentences. I sometimes see native speakers also use any with singular countable nouns in negative sentences. What is the rule?

Here's the example:

• There isn't any pen in my bag.

I know most people would say "There are no pens.." or "There are not any pens..." but when can I use any with singular countable nouns in negative sentences? I cannot provide any context. I am sorry for that.

Answer 1

In US English

There isn't a pen in my bag

or

There isn't any pen in my bag

are grammatical but rare. The thought would usually be expressed as

There aren't any pens in my bag.

or

There are no pens in my bag.

The point being that one pen is likely to be as useful as any other pen so the relevant answers to the question of whether you have A pen are "none" or "at least one."

There are exceptions, for example if you are trying to distinguish between one thing and others of like kind.

That isn't any ring. It belonged to my dead grandmother.

So

Is not (Isn't) any singular countable noun

is grammatical, but is normally reserved for special citcumstances.