Aristotle establishes how things are named and categorized, introducing the distinction between what is said of an underlying subject and what exists in one. He defines ousia (substance) in its truest sense as what is neither said of nor exists in anything else—the individual thing itself—and shows why individual things are the foundation on which all other things depend.

Terms in today's reading — logos: a reasoned account · ousia: substance — what a thing most truly is