Today should be the last day I talk about Aristotle's Physics. He gives two more proofs for the existence of God, these ones based on changes and cause and effect.
This is similar to his proof based on motion. Aristotle's proof from motion started from the premise that nothing moves itself. Similarly, his proof from change starts from the premise that nothing can change itself. Otherwise, this leads to the illogical situation, where a thing is actively changing itself, while passively being changed by itself. This means it is both active and passive in the same action.
To look at it another way, when a thing changes, it gains a new quality which was previously a potential quality. For an example, let's take me logging on to the Internet. When I do that, I change from being a potential Internet user to an actual Internet user. Note that it is impossible for me to be a potential Internet user and an actual Internet user at the same time; it's either one or the other, not both.
Anything that is in the process of change is being changed by something else. Changes cannot go on indefinitely, and you can't have an infinite line of things changing each other, in the same way that you can't have an infinite line of things moving each other. The series of changes has to start somewhere, with an unchanged changer.
If you prefer, you can replace "change" with "cause and effect". If you have an effect, there must be a cause attached to it, because nothing can cause itself. A series of "cause and effect" can't go on forever; logic tells us that the series starts with a first cause. Therefore, there must be a general first cause, an uncaused causer.
Yes, I'm kind of rushing the explanation here, but I know you readers are smart enough to follow along. Aristotle's three proofs basically boil down to this:
1. (Pick one: motion, change, causes) are not self-generated. They are only transferred.
2. You can't have an infinite series of (motion/change/causes) being transferred from one thing to another.
3. Therefore, the (motion/change/causes) we experience in the world started with something that is not (moved/changed/caused).
The form of the argument is the same in all three proofs, although the content is different in each proof. Aristotle invented logic, and as you would expect, his deduction is 100% logical; the conclusion naturally follows from the two premises. Whenever someone disagrees with Aristotle's argument, it is either because they believe Premise 1 is false, or they object to something else entirely, such as the tendency to identify the unmoved mover with God.
(John Locke, whose portrait is used for Corbin Penvellyn in Nancy Drew: Curse of Blackmore Manor, is one of the few people who disagreed with Premise 2. His argument is based on the idea that something can have a beginning and still be eternal, but that'd take us a bit off-topic, unless you want me to explain it in more detail.)
If we take these three proofs for the existence of God, what kind of god emerges? Aristotle proves that this god is non-physical, and that it is responsible for movement and change in the physical universe. It is also responsible for causes, but that's more of a secondary quality; once this god caused movement, it ipso facto became responsible for causes.