PHILOSOPHY OF NATURE
Aristotle’s classification of the sciences, as we have seen, divides them firstly into the theoretical, which aim at knowledge for its own sake, the practical, which aim at knowledge as a guide to conduct, and the productive, which aim at knowledge to be used in making something useful or beautiful. The theoretical sciences are subdivided into ‘theology’ (or metaphysics), physics, and mathematics. Physics deals with things that have a separate existence but are not unchangeable (i.e. with ‘natural bodies’, which have in them a source of movement and rest), mathematics with things that are unchangeable but have no separate existence (i.e. with numbers and spatial figures which have only an adjectival existence, as qualifying substances); theology with things that both have separate existence and are unchangeable (i.e. with the substances which exist free from any connexion with matter); it owes its name to the fact that the chief of these pure substances is God.’ ‘Physics’ as thus defined is expounded by Aristotle in a long series of works. That these are thought of as forming a unity is indicated by the opening of the Meteorologica; Aristotle there claims to have dealt (1) with the first causes of nature (i.e. the constituent elements which in Physics I., II. he shows to be involved in all change), and with natural movement in general (Physics III.-VIII.); (2) with the order and movement of the stars (De Caelo, I., II.), the number and nature of the bodily elements and their transformation into each other (De Cuelo, III., IV); (3) with coming to be and passing away, in general (De Generatione et Corruptione). He proposes to deal (4) with ‘the things that happen in accordance with nature, but a nature less ordered than that of the first (or celestial) element, in the region that borders most closely on the movement of the stars’2
(Meteorologica); and (5) with animals and plants both in general and according to their kinds (the biological works).