* summarized from Edward Feser’s book, Five Proofs of the Existence of God, Ignatius Press, 2017
1. The Aristotelian Proof
Since change actually occurs, and change is defined as the actualization of a potential, there must exist something that can actualize potentials without itself being actualized. This something is purely actual because it lacks any potentiality. Any actualization of a potential requires a cause, whereas what is pure actuality does not. This is the “unmoved mover” of Aristotle, characterized as God.
2. The Neo-Platonic Proof
Things that we experience are composite; the ultimate cause of composites must itself be non-composite, or absolutely simple. Composite things require a cause because there must be some principle outside them that accounts for the composition of their parts. What is non-composite has no parts to be put together, therefore could not be caused. Neither the universe, or even a multiverse could be uncaused, necessary, or self-explanatory because they are composite.
3. The Augustinian Proof
Universals, propositions, possibilities, and other abstract objects must ultimately be grounded in a divine intellect.
4. The Thomistic Proof
For any of the contingent things of our experience, there is a real distinction between its essence and its existence. Nothing like this could exist unless it was caused to exist by something in which there is no such distinction. Something whose essence just is existence need not have existence conjoined to its essence and therefore does not need a cause. The universe, Big Bang, quantum events, or laws of nature could not be uncaused causes. Only something whose essence just is essence itself could be an uncaused cause.
5. The Rationalist Proof
There cannot be an explanation of the existence of any of the contingent things of our experience unless there is a necessary being. The universe is contingent rather than necessary and thus could not provide an ultimate explanation.