On Generation and CorruptionAristotle

On Generation and Corruption addresses the most basic kind of change: how substances come to be and pass away. Aristotle distinguishes generation (coming-into-being) and corruption (ceasing-to-be) from alteration (change of quality), growth (change of quantity), and locomotion (change of place). The treatise asks what makes substantial change possible and how it differs from mere modification.

The key move is Aristotle's theory of the elements. Earth, water, air, and fire are constituted by combinations of two pairs of contrary qualities: hot and cold, wet and dry. Transformation of one element into another is possible because they share a quality: water (cold and wet) can become air (hot and wet) by exchanging cold for hot. Generation and corruption of compound substances involve the mixture and separation of these elements. Aristotle distinguishes genuine mixture, in which the ingredients are transformed into a new substance with its own properties, from mere juxtaposition, in which they retain their identities side by side.

The treatise also engages the atomists. Against Democritus, Aristotle argues that matter is continuous, not composed of indivisible particles separated by void. Change requires real qualitative differences in matter, not just rearrangements of shape and position. On Generation and Corruption provides the physical theory that underlies Aristotle's biology and his account of the natural world as a domain of purposive change.