ecome apparent.
1. Some things are in motion, as evidenced by our senses.
2. Whatever is moved is moved by something else.
3. Movement involves change from potentiality to actuality.
4. Something in potentiality must be moved by something in actuality.
5. Nothing can be both in potentiality and actuality at the same time and in the same respect.
6. Thus, a thing cannot be both mover and moved in the same respect, or, it cannot move itself.
7. There can be no infinite regress, because if there is no first mover there can be no other movers, and hence, no motion.
8. Therefore, there must be a first mover which is not itself moved, "and this everyone understands to be god."
Premise One is best taken in a common sense manner rather than given the abstract, metaphysical interpretation that some scholars have tried to impose on it, since the former allows the First way to start off with an unimpeachable truth about the material world. Premise Two is a more difficult proposition because it is unclear whether Aquinas meant that everything in motion is being moved simultaneously, which admits of many fatal counterexamples, or whether he meant that everything in motion had at one time or another been moved, a much more defensible statement. Even if we charitably take the second interpretation, it still won't necessarily lead us to an unmoved mover, because Aquinas himself said he found nothing inconceivable about an endless series of "temporarily ordered causes" of the sort we are discussing here. In other words, even if it is admitted that whatever is moved is moved by something else, it remains possible for a thing in the material world to do all of the moving: the mover has not been proven to be eternally unmoved, just unmoved at the particular time that it moves something else.
Furthermore, Aquinas has not adequately proven that a thing must be moved by something outside it. "If a thing cannot ...