The Prime Mover (and a word on logic)

Aristotle’s universe is a universe of motion and change (kinēsis) — and he argues that motion is eternal: it never began and never ends, for any supposed “first moment of motion” would itself be a change needing a prior cause. But an eternal, ongoing process still needs a source. What keeps the whole system going? This is the argument of Physics VIII and Metaphysics Λ (Book XII).

Start from a principle: whatever is moved is moved by something else. A stone is thrown by a hand, the hand driven by muscle, the muscle by the soul, and so on. Each mover in the chain is itself being moved by a prior mover. The question is whether that chain can run backward forever.

Aristotle says it cannot — not in the sense that matters. An infinite regress of moved movers explains nothing, because every link merely passes along motion it received; none of them is the genuine origin. A chain of borrowers can’t account for the money if no one ever had any. To ground the eternal motion of the cosmos, there must be a first mover that starts the transmission without being started — an Unmoved Mover (to prōton kinoun akinēton), the Prime Mover.

What must this first mover be like? It is moved by nothing, so it never changes — it is eternal and immutable. Since matter is the potential to be otherwise, and it has no potential left to actualize, it has no matter: it is pure form. And since change is potential becoming actual, a thing with no unrealized potential is pure actuality (energeia) — fully, timelessly at its end. No matter, no motion, no potential: only complete actuality.

Now the puzzle that makes the doctrine famous: if the Prime Mover never moves, how does it move anything? Aristotle’s answer is elegant. It moves not as an efficient cause (by pushing) but as a final cause — as an object of love and desire. It moves the cosmos “as the beloved moves the lover” (Metaphysics Λ.7, 1072b). The heavens, drawn toward its perfection, strive to imitate it in the most perfect motion available to them — eternal circular rotation.

And what does a being of pure actuality, needing nothing, do? Only the highest activity: it thinks. But it cannot think about anything lesser or external without depending on it, so its thinking has the one worthy object — itself. The Prime Mover is “thought thinking itself” (noēsis noēseōs, Metaphysics Λ.9). Its life is perfect, eternal self-contemplation — theōria — and this, Aristotle says, is the divine life, the best and most continuous life there is.

A closing word on logic. Alongside all this, Aristotle founded a discipline from scratch: formal logic, collected in the works later called the Organon (“the instrument”). His great discovery was the syllogism — inference whose validity depends on form, not content. All men are mortal; Socrates is a man; therefore Socrates is mortal. Swap in any terms and the pattern still forces its conclusion. Aristotle also gave the first theory of demonstration (apodeixis): genuine scientific knowledge is what can be derived by valid syllogism from first principles. It is no exaggeration that he invented logic as a field — and it stood essentially unrivalled until the nineteenth century.