Metaphysics

A collection of fourteen treatises gathered after Aristotle's death under a title meaning 'the books after the Physics'. They pursue what he calls first philosophy: the study of being as being and of the first causes of things. Book I opens with the claim that all humans by nature desire to know, and reviews earlier thinkers in the light of his four causes. Book III lists the central puzzles. Book IV argues that being is said in many ways but always with reference to substance, and defends the principle of non-contradiction against anyone who denies it. Book V is a dictionary of key terms. Books VII to IX, the core, ask what substance is, weighing essence, universal, genus and underlying subject, and develop the ideas of form and matter and of potentiality and actuality. Book XII argues for an eternal unmoved mover whose activity is thought thinking itself. The last two books criticise Plato's forms and numbers.

It defines the questions metaphysics still asks about substance, essence, causation and necessity, and much medieval and modern philosophy is written in its vocabulary.