Arguments for God's Existence
From the eleventh century to the present, each argument stated as its defenders state it and named for the load-bearing premise it turns on — the hinge, the point at which it is argued and answered. The library quotes the sources and draws no conclusion.
Thomas Aquinas & The Five Ways
Summa Theologica I, q. 2, a. 3 · c. 1265
First Way
From Change
The hinge: that no potential can actualize itself
Second Way
A First Cause
The hinge: whether an essential causal series can regress forever
Third Way
From Contingency
The hinge: the Principle of Sufficient Reason
Fourth Way
From Degrees
The hinge: that the maximum of a perfection causes it in all else
Fifth Way
From Design
The hinge: the inference from design to a designer
Know before reading
Aquinas is not laying out his full case here — each way summarizes an argument he develops at length elsewhere, above all in the Summa Contra Gentiles. He wrote not for modern atheists but for readers who already took an ordered, God-filled cosmos for granted, to show that reason, not faith alone, could reach the God they already worshipped.
None of the Five Ways depends on the universe having had a beginning; Aquinas famously didn't believe that could be proved by philosophy.
“The same holy Mother Church holds and teaches that God, the beginning and end of all things, may be certainly known by the natural light of human reason, by means of created things.”
The First Vatican Council, Dei Filius (1870), ch. 2 · tr. Philip Schaff, The Creeds of Christendom PD