 According to traditional medieval interpretation, Aristotle’s ten categories (substance and nine accidental categories, such as quality, quantity, and relation) represent both ontological and conceptual divisions of the world. On the one hand, the world really is divided into ten ontologically distinct types of things; and on the other hand, our conceptual scheme employs the ten categories because there is an isomorphism between how things really are and how we understand them to be (see the entry  on medieval theories of the categories).