Any science that purports to deal in basic explanation must run its facts back to their utmost source. That is why Aristotle, like his predecessors, begins the study of natural being with the search for its ultimate principles. Specifically, what he wants to know at the outset is the intrinsic principles, the primary constituents; the extrinsic principles, efficient and final cause, are probed later on. Accordingly, the notions set forth in the present chapter approximate what the moderns would generally call a theory of matter.
The chapter opens with a synoptic view of Book I of the Physics. Next, we follow Aristotle in his quest of the principles of nature: form, privation, matter. Then, having established the principles universally, we turn for a moment from the Physics to De Generatione, to consider with Aristotle the two essential kinds of change, substantial and accidental. This done, we return to Book I to declare the substantial and accidental structure of bodies. The chapter then closes with a comparative review of hylomorphism and other theories of matter. 1