The cosmological argument is an argument for God's existence based on the belief that the world must have been caused by some supreme being. The term “cosmological” comes from the Greek word “kosmos” which means “world.”
According to the cosmological argument, all contingent things, including our world, must have a cause. But since there cannot be an endless series of causes, there must be one “uncaused cause” that started the process of contingent beings. For Aristotle, this ultimate cause of motion or change was the “Prime Mover.”
Saint Thomas Aquinas refined Aristotle’s cosmological argument and used it in defense of the Christian God. In short, the cosmological argument, within a Christian context, goes like this: The world could not exist on its own so there must have been a first cause, who himself has no cause, that brought it into being. This first cause is God.
The cosmological argument is still a major argument for theism today. Some have argued against this view saying that matter is eternal. Others have said that even if it is true that some being caused our universe to exist, this does not prove the existence of the Christian God. All it shows is that there is some powerful being that created the universe.
The cosmological argument is one of four major arguments for the existence of God along with the teleological, ontological, and moral law arguments.