Aristotle's Metaphysics Z.17 and the Project of First Philosophy

I argue that the famous discussion of substance and essence in Aristotle's Metaphysics Z offers a direct and positive response to the central question of 'first philosophy' or "metaphysics" as to the first principles and causes of being qua being: Z is designed to establish that essences are the first principles and causes of composite substances insofar as they are. Two moves are crucial to my argument: First, I argue that the goal of the final chapter of Z (that is, Z.17) is to give an account of essences as the first causes of being of composite substances. Second, I argue that the guiding question of Z 'What is substance?' should be understood as a causal question that seeks the 'what it is' of composite substances. Overall, contrary to prominent interpretations, it emerges that Z is neither an independent treatise on substance nor a negative aporetic contribution to first philosophy but rather a core part of Aristotle's positive first-philosophical project. I also argue that this reading of Z is compatible with Aristotle's characterization of first philosophy as 'theology'.