The Cosmological argument is an attempt to prove that God exists by appealing to the principle that all things have causes. The most basic form of the argument would be as follows: there cannot be an infinite regress of causes, therefore, there must be an uncaused cause: God. Thomas Aquinas (1224-1274) had a version of the Cosmological Argument called the Argument from Motion. It is from Aquinas' argument that we get the phrase unmoved mover. For more information, please see The Cosmological Argument.