This dissertation is concerned with the relationship between essence and explanation in Aristotle's philosophy of science and philosophy of nature. My central theme is that Aristotle's concept of the nature of a substance ties these two areas of his philosophy together. In his philosophy of science it manifests itself in the notion of the essential nature of a kind, in his philosophy of nature it finds its expression in the essential potentialities of a substance. I argue that the explanatory dimension of Aristotle's philosophy of science lies not in his concept of scientific demonstration but in its implicit recourse to a substance's essential potentialities.
A scientific demonstration, I maintain, does not constitute an explanation, nor does it involve explanation in performing its demonstrative function. Rather, demonstration gives rise to understanding; the apprehension that something belongs in the essential nature of a kind. I call this scientific exposition, rather than scientific explanation.
In order to 'recover' the explanatory dimension of Aristotle's philosophy of science I consider, first, the structure of his essentialism, and second, his metaphysics of change in which the notions of potentiality and actuality play a central role. It is in these two aspects of his philosophy that the substantial content of Aristotle's definition of 'nature' (phusis) is located. A nature, according to Aristotle, is a principle of change belonging to a thing in itself; but what is essential to a kind consists of what belongs to the members of the kind in itself, and a potentiality is defined as a principle of change.
It is through this link that Aristotle's philosophy of science finds its underlying explanatory dimension. For when, through scientific demonstrations, we 'unpack' the essential nature of a kind, what we lay bare are the essential potentialities of each of the members of the kind, the actualizations of which constitute the various changes that those substances may undergo. That is, we lay bare what it is in the nature of things that accounts for their behavior in various diverse circumstances.