Universal is not a(n) (individual) substance

Why does Aristotle think that a universal is not a(n) (individual) substance (Categories) or (but not both) that primary substance is the composite of form and matter (Physics)? How can he think that when he is willing to say that substance is essence (Metaphysics)? How does Aristotle account for change in the excerpts we read from the Physics and Metaphysics? What is a conceptual thread you can run through Aristotle’s Physics and Ethics?

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