A first cause, or an endless regress?
On the axis: Existence of God · the series of causes
Must the series of causes have a first term that depends on nothing, and why would that term escape the question we put to everything else?
Justification
Thomas rejects both fideism, which would treat God's existence as a mere matter of faith, and 's ontological argument, which claimed to deduce it from the concept alone: for a finite mind, God's existence is not self-evident, it is demonstrated from effects. Hence the , which all start from a fact of experience (motion, causation, contingency, degrees of perfection, the ordering of ends) and rise, to avoid an infinite regress, to a first term: an unmoved mover, an uncaused cause, a necessary being. Theism is thus held to be rationally established, and not merely believed.
Whatever is moved is moved by another; we must therefore arrive at a first mover moved by nothing, and this everyone understands to be God.Summa Theologiae, Ia, q. 2, a. 3 (the first way)
Summa Theologiae, Ia, q. 2, a. 3 (the Five Ways) · Summa contra Gentiles, I, 13
Justification
In the Dialogues Concerning Natural Religion, Hume dismantles the argument from design: the order of the world warrants no secure inference to an infinite, wise and good creator, above all given evil. Without professing firm atheism (he allows a vague cause or causes of order), he empties theism of any determinate content: the position leans clearly toward agnosticism and atheism.
Dialogues Concerning Natural Religion (esp. parts V, VIII and XI) · The Natural History of Religion