Metaphysics

Aristotle's Metaphysics is a collection of treatises, likely never organized by Aristotle himself into the form we have, and the difficulty of the text matches the difficulty of its subject. It investigates "being qua being," the principles and causes of whatever exists insofar as it exists. Later tradition called this "first philosophy."

The opening books survey and critique earlier thinkers. Aristotle works through the Presocratics, the Pythagoreans, and Plato, testing each account of ultimate causes. By Book IV he reaches the principle of non-contradiction, which he defends not by proof (it is too fundamental for that) but by refutation of anyone who attempts to deny it. Books VII through IX form the core of the work: an investigation into substance, the primary sense of being. Substance is what exists in its own right, not as a quality or quantity of something else. Aristotle distinguishes matter (what a thing is made of), form (what makes it the kind of thing it is), and the composite of both. Form is prior; it is the answer to the question "what is it?" The analysis of potentiality and actuality in Book IX extends this. What a thing can become is intelligible only in light of what it is when fully realized.

Book XII turns to theology. There must be an eternal, unmoved mover, pure actuality with no potentiality, whose activity is thought thinking itself. This is God, not as creator in the biblical sense, but as the final cause that draws all motion and change toward itself.

The Metaphysics gave the Western tradition its vocabulary for discussing being, substance, form, matter, potentiality, and actuality. Every subsequent metaphysician either builds on Aristotle's framework or defines a position against it.