Early in his Summa Theologica, Thomas Aquinas addresses the question of whether the existence of God is self-evident.
Aquinas asks whether God exists and proposes five ways of proving God’s existence: motion, efficient cause, possibility and necessity, gradation, and governance.
These arguments were not original to Aquinas, but his synthesis and restatement of the argument has engaged philosophers and theologians for almost a millennia.
The following is a summary of Aquinas’s five ways of arguing for God’s existence:
First way: the argument from motion—everything in motion must be put into motion by another; this first mover is God
Second way: the argument from efficient cause—the chain of secondary causes and effects began with an uncaused first cause, which is God
Third way: the argument from necessity—contingent beings depend for their existence on a necessary being, which is God
Fourth way: the argument from gradation—degrees, or grades, of perfection in beings presuppose the existence of a perfect being, which is God
Fifth way: the argument from governance—nature acts with an end in mind as if designed by a designer, which is God
The five ways can be considered one way of arguing for God’s existence, which was later called the cosmological argument.
The Kalam Cosmological Argument Part 1