This paper argues that the discussion in which Aristotle engages in Metaphysics ΖΗ has the same starting-point as natural science: the principles of changing substances. These inquiries are nonetheless distinct because natural science uses these principles in its detailed investigations into natural substances, whereas ΖΗ reflect on the principles themselves. ΖΗ are an integral part of Aristotle’s inquiry into the principles of all substances, changing and unchanging: they are not merely preliminary to an inquiry into the latter kind. They are (...) also an integral part of Aristotle’s ‘first philosophy’, alongside theology’s study of the nature and activity of unchanging substances. (shrink)

Discussions of Aristotle’s Metaphysics Z tend to treat it either as an independent treatise on substance and essence or as preliminary to the main conclusions of the Metaphysics. I argue instead that Z is central to Aristotle’s project of first philosophy in the Metaphysics: the first philosopher seeks the first causes of being qua being, especially substances, and in Z, Aristotle establishes that essences or forms are the first causes of being of perceptible substances. I also argue that the centrality (...) of Z to first philosophy is compatible with its status as theology. (shrink)