"I have reason to be worried."
"I have a reason to be worried."
"Reason" is both countable and uncountable. Could both sentences be correct?
..
They're both correct.
Do they mean the same thing?
I have reason to be worried - My worry is justified.
I have a reason to be worried/for being worried - One thing is causing my worry.
Context is always important; labelling is rarely important.