The Cosmological argument was created by philosophers as an attempt to show why believing in God is logical. It claims that from examining the fact that the universe exist, you can work out the reason for the universe existing.
The universe exists. Why does it exist? Something must have caused its existence.
Aquinas' Five Ways
In his book Summa Theologie Aquinas came up with five ways that explain why believing in God was a rational thing to do. The first three are often referred to in reference to the Cosmological Argument:
Way 1. The unmoved mover
We can observe that things in the universe are in a state of change.
Everything that is in a state of change is in movement from actuality to potentiality.
The same thing can not be potentially and actually the same thing at the same time.
e.g. If something it hot, it cannot be potentially hot but can be potentially cold.
So, everything in a state of motion must be put into this state by another thing,
But the chain of movers 'cannot go on infinitely because then there would be no first mover'
Conclusion: There must be a first mover
Way 2. The uncaused causer
Nothing is an efficient cause of itself.
Efficient causes follow in order: a first causes a second cause, a second causes a third and so on.
It is not possible for efficient causes to go back to infinity, because if there is no efficient first cause, there will not be any following causes.
Conclusion: It is necessary for there to be a first efficient cause, which is God.
Aquinas is looking at what begins the chain of movement…