General principle: definitions put a thing into a category, and then explain how that thing is different from other things in the same category.

I don't think definitions are how people generally use words-- prototype theory seems more accurate. Prototype theory says that people have best examples of concepts, and then rank actual things according to how close they are to the prototype.

It would be nice to have a theory about how to decide when to use definitional thinking and when to use prototypes, but I don't.