The subject of the present research work is the first of the so-called 'central books' of Aristotle's Metaphysics, Book Z. The aim is to show how the theory of substance developed in Metaph. Z constitutes a crucial stage in the more general process of de-construction and de-mathematization of the Platonic-academic system that occupies a substantial part of Aristotelian philosophical speculation in the Metaphysics. The continuous comparison between the status of natural substances and that of

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... metric mathematical entities is far from being accidental in the context of the investigation of substance in Metaph. Z. On the contrary, it stands as a programmatic choice oriented to place physics, and not the abstract model of mathematics, as the propaedeutic science that from natural substances - assumed as the main object of the examination of the book Z - leads to the causes and first principles of what is. In this sense, on a methodological level, the object of this thesis is not the book Z in its entirety, but rather the identification and exegesis of those passages where there is an instrumental use of mathematical-geometric examples, which Aristotle uses in the course of his investigation of substance to reaffirm the fundamental role of physics.