What are the primary and secondary substances?
Aristotle defines substance as that which is “in the truest and primary and most definite sense of the word, is that which is neither predicable of a subject nor present in a subject” (Chapter 5, Edghill Translation). A primary substance is that “which neither is said of a subject nor is present in a subject” (Chapter 5, Edghill Translation), while a secondary substance is that “which is said of a subject but is not present in a subject”. To make this clearer we can say that a substance is anything that has an independent existence. Cows, cats and Kangaroos are all substances that we encounter in the world around us. Now take one of those substances, say your cat Simba, this individual cat is a primary substance while his catness, the kind of thing he is, represents a secondary substance. We can also say that it is the primary substance which is capable of having something predicated on it. In our example here catness is predicated upon the primary substance of Simba.