@guigus,
I did show you a flaw in your reasoning.
I asked you to give an example of an idea that does not exist.
You gave the example "a unicorn", saying that it "doesn't exist because it is just an idea..."
So what you are saying is that "The
idea doesnt exist because it is
just an idea".
So... what? Sand doesn't exist because it is just sand?
Like I said, I don't think you are making a distinction between an idea as a conceptual construct (all ideas are conceptual construct), and a unicorn (an example of such a constuct).
Heres a possible definition of a unicorn:
Unicorn: A mythical creature that resembles a horse with a single horn in it's forehead, pointing straight forward at an upward angle. We have no indications that such a creature has ever existed anywhere but in human imagination.
Pretty good explanation of unicorn, wouldn't you say? A hell of a lot more meaningful than:
Unicorn: a nonexistent.