Three of his Five Ways: the argument from an unmoved mover, the uncaused cause, and possibility and necessity.
The Kalam Argument
Everything that exists must have a cause for its existence
The universe exists
Therefore the universe must have a cause.
“That than which no greater can be conceived.” i.e. God
“God has wanted to make an orderly world because beauty is a good thing.”
“God is a necessary being because something must have started the process off. He is not contingent on anything else.”
“Some thing causes in all other things their being, goodness, perfections… and this we call God”
“We can never ascribe to a cause any qualities but what are exactly sufficient to produce the effect.”
Even if there was a first cause – why God?
“We observe an event and a consequence and separate the two into cause and effect. But because we are limited and cannot get outside the universe, so we cannot assume they are always linked.”
“If God is the first cause then he is not the God of Classical Theism because the earth is flawed.”
“There is no value in faith, it weakens man and prevents him from taking responsibility.”
“The existence of the universe is Brute fact – it just is.”