Philosophy
The Metaphysics of Properties and the Problem of Universals
Quick fact
The problem of universals has been debated for over 2,000 years, from Plato's theory of Forms to modern trope theory, and it remains one of the deepest puzzles about the structure of reality.
Why this is interesting
You see two red roses. You know they are both red. But what is that 'redness' they share? Is it a thing that exists somewhere, or just a name we give to similar experiences?