By natural, what I mean is that rarely do people classify a ball as a round object in their head or a sphere with a particular volume in their head. They just think of it as a ball. And if it has a colour, they may classify it as a “yellow ball” in their head, and not “a sphere” or “an object” or “an object with volume”. It seems that most objects can be classified in an infinite number of ways, yet only one or a few classes seem more natural than others.
What causes this? Is this related to some sort of category being fundamentally more natural than another? Or is this simply an evolutionary instinct to categorize things in a certain way?