The second way-Cause
Aquinas concentrates on the idea of efficient cause.(the agent that makes things happen)
Everything has a cause
Nothing can cause itself to exist
Because Aquinas rejects infinite regress, there must be an uncaused causer.
It isnt possible for something to be the efficient cause of itself.
It is not possible to go back into infinity with efficient causes-there must be a first efficient cause which we call God.
To deny the idea of infinite regress there must be an uncaused and eternal being which does not rely on anything else for its existence, otherwise it would have to have had a begining and have been caused to exist by something else and wouldnt be the first cause.
All things have been caused by something else.
Nothing is the cause of itself or has within itself the cause for its existence because it would have had to have existed before itself which is nonsense.
Universe must have been cause by something outside of itself.
The first cause is God.
The third way-Contingency
Contingency-an event that depends on something else which may or may not happen.
Things do not contain the reason for their own existence, but depend on an external cause.
Everything in the universe exists contingently-this means that they depend on other thing for their existence, they have a start and an end.
The fact that things are contingent means that they cannot last forever.
If time is infinite then there must have been a time where nothing existed.
Everything depends on something for its existence and everything started existing and will stop.
If there was a time where nothing existed then there would still be nothing, as nothing can make itself exist.
Nothing caould begin to exist from nothing.
So there must be something non dependent or enccessary which is God.