An idea · Classical Greek · first attested 340 BCE
The Unmoved Mover
There must be a first cause that itself is uncaused.
Aristotle's argument: every motion has a cause; an infinite regress of causes is impossible; so there must be a first cause that itself is unmoved. He calls it Nous, pure thought thinking itself. Aquinas turns this into the second of his Five Ways and identifies it with God.