Philosophy
The Problem of Universals and Nominalism
Quick fact
Medieval philosophers debated universals for centuries, with nominalists like William of Ockham arguing that only individual things exist, and universals are merely names (hence 'nominalism' from the Latin 'nomen' for name).
Why this is interesting
Think about the color red. It appears in many objects, but does 'redness' itself exist somewhere? Or is it just a name we use for similar experiences?