Four types of cause according to Aristotle:
Aristotle's argument:
1. Every effect has an efficient cause (similarly, a final cause, etc.).
2. (Assume:) every cause is itself an effect and has itself a cause.
3. Therefore, causes stretch back to infinity.
4. But this is not possible ("causes cannot go on ad infinitum" -- A.)
5. Therefore, a first cause does not itself have a cause.
6. The first cause, the Unmoved Mover, is God.