That’s what Seminar was about on Thursday. Because he posits infinite time and infinite movement (because time is an attribute of movement), but is unwilling to accept an infinite regression of causes, Aristotle deduces the existence of an “unmoved mover” that is eternally existent, has no magnitude nor motion, but eternally causes motion in the rest of the celestial sphere. Probably it also resides at the circumference of the sphere, because that’s where motion is fastest and most regularly ordered. Essentially an impersonal God.
Someone studying the same section but a different class said that the main significance of the unmoved mover is that it highlights the necessity of either accepting the possibility of something outside of the observable universe, or the possibility of either uncaused change or an eternal regression of causes within the observable universe. None of these possibilities seems logically comfortable. Somebody brought up: well, A. has to reason that way because he doesn’t know about things like the Big Bang. That is to say, I suppose, that he was more familiar with eternal rather than finite motion, and the converse is true of us. We have observed that the universe is not quite as stable as A. thought, and is moving slowly apart rather than in an infinite circular motion. Besides which, we are willing to believe in finite motion because Christianity believes in finite time — in a definite Creation — as the ancient Greeks apparently did not (Timaeus excluded).