Doodledog
Oh yes, of course you are right.
I know it's far from obvious from this thread, but I used to be rather good at grammar ?. I think I need a refresher, don't I?
I think the penny is dropping, though. Although I thought that in both of my examples the word was being used as an adjective, the 'you are difficult' one sounded to me more like 'a class of person', which is why I thought it was different. But unless it takes an article in the example, it is still an adjective.
Phew!
Thanks for your patience, everyone. It's much appreciated.
No expert but I think "difficult" is always an adjective even when it's being used as a noun, my reasoning is that the noun it is describing has been omitted but is still implied. eg when it's being used to describe a group of people , the noun "people" is left out, in the example given earlier from the OED used in climbing, the difficult describes climbs, which has been left out but is implied. So being pedantic, which is what this post is about, in certain cases I would describe "difficult" as an adjective being used as a noun but in the cases given by the OP "difficult" is an adjective.