Book 12
4
Another is immutable , which certain thinkers hold to exist separately; some dividing it into two classes, others combining the Forms and the objects of mathematics into a single class, and others recognizing only the objects of mathematics as of this nature.These three views were held respectively by Plato, Xenocrates and Speusippus. Cf. Aristot. Met. 7.2.3, 4; Aristot. Met. 13.1.4, and see Introduction. The first two kinds of substance come within the scope of physics, since they involve motion; the last belongs to some other science, if there is no principle common to all three.
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Sensible substance is liable to change. Now if change proceeds from opposites or intermediates—not however from all opposites (for speech is not white), but only from the contraryCf. Aristot. Met. 10.7.—then there must be something underlying which changes into the opposite contrary; for the contrariesi.e., contrary qualities. Cf. Aristot. Met. 8.5.1. do not change.
1
Further, something persists, whereas the contrary does not persist. Therefore besides the contraries there is some third thing, the matter . Now if change is of four kinds, in respect either of substance or of quality or of quantity or of place, and if change of substance is generation or destruction in the simple sense, and change of quantity is increase or decrease, and change of affection is alteration, and change of place is locomotion, then changes must be in each case into the corresponding contrary state.
