I like to think about it as this: numbers are a human invention, but quantity is a property of the universe. The laws of physics, including all types of conserv

I like to think about it as this: numbers are a human invention, but quantity is a property of the universe. The laws of physics, including all types of conservation, take care of that. Quantity takes care of ensuring many derived properties (rules) that numbers show and which can be expressed abstractly (complex math). Studying the properties of a complex self-consistent system is interesting, and sometimes, when it reveals an interesting resulting property, it can be traced all the way back to the original natural property of quantity, and applied in a practical way in the world. Other times, it can't, and it remains a curious interesting fact in the realm of the abstract system.