The First Way: Argument from Motion
1. Our senses prove that some things are in motion.
2. Things move when potential motion becomes actual motion.
3. Only an actual motion can convert a potential motion into an actual motion.
4. Nothing can be at once in both actuality and potentiality in the same respect (i.e., if both actual and potential, it is actual in one respect and potential in another).
5. Therefore nothing can move itself.
6. Therefore each thing in motion is moved by something else.
7. The sequence of motion cannot extend ad infinitum.
8. Therefore it is necessary to arrive at a first mover, put in motion by no other; and this everyone understands to be God.
The Second Way: Argument from Efficient Causes
1. We perceive a series of efficient causes of things in the world.
2. Nothing exists prior to itself.
3. Therefore nothing [in the world of things we perceive] is the efficient cause of itself.
4. If a previous efficient cause does not exist, neither does the thing that results (the effect).
5. Therefore if the first thing in a series does not exist, nothing in the series exists.
6. If the series of efficient causes extends ad infinitum into the past, for then there would be no things existing now.
7. That is plainly false (i.e., there are things existing now that came about through efficient causes).
8. Therefore efficient causes do not extend ad infinitum into the past.
9. Therefore it is necessary to admit a first efficient cause, to which everyone gives the name of God.
cont...