The Cosmological argument argues for the existence of God a posteriori based on the apparent order in the universe. For Aristotle, the existence of the universe needs an explanation, a cause, as it could not have come from nothing. Nothing comes from nothing so since there is something, there must have been some other thing that is its cause. Aristotle rules out an infinite progression of causes, so, that led to the conclusion that there must be a First Cause. Likewise with motion, there must have been a first cause; Aristotle calls this the ‘Prime Mover’. There is a God, says Aristotle -for how else does motion begin? Whilst this argument does generally offer some support for the existence of God, it does not prove his existence.
Aquinas believed that, since the universe is God's creation, evidence of God's existence can be found in his creation using intellect and reason, as such a concept of God is beyond all direct human experience. Hence, he devised his 'Five Ways,' 5 a posteriori arguments for the existence of God, based on our empirical experience of the universe. The Cosmological argument rests on the first three of Aquinas' Five Ways. The first way is called the argument from motion or ‘change’. It is in this first way that Aquinas follows Aristotle’s ‘prime mover’ thesis. The first way (The 'Kalam' argument) follows as:
• Everything in the world is moving or changing
• Nothing can move or change by itself
• There cannot be an infinite regress of things changing other things
• Therefore there must be a Prime Mover (or changer)
• This is God, thus God exists

The 2nd way: Argument from causation states that
• Everything in the world has a cause
• Nothing is the cause of itself
• There cannot be an infinite regress of causes
• Therefore there has to be a first cause to start the chain of causes
• This first cause is God, thus he exists

The 3rd way: Argument