Five Ways

The Five Ways are Thomas Aquinas‘s five short proofs of the existence of God in the Summa Theologiae First Part, Question 2, Article 3. Each Way takes the form of an argument from a feature of the world to a first cause of that feature, identified at the end with what people commonly call God.

The First Way argues from motion to a first unmoved mover. The Second argues from efficient causation to a first uncaused cause. The Third argues from contingency to a Necessary Being. The Fourth argues from gradations of perfection to a maximum that is the source of those gradations. The Fifth argues from the apparent goal-directedness of natural things to an intelligent director.

The Five Ways are short because they are starting points, not finished arguments. Aquinas treats each one as opening a question that the rest of the Summa will refine. The First Way and the Second are versions of the Cosmological Argument. The Fifth Way is a version of the Teleological Argument. The Third Way is the most-cited modern reference for arguments from contingency.

What the Five Ways are not is what they are most often taken to be: complete arguments for the God of Christianity, defended in their own right against modern objections. They are theological starting points within a system that takes the existence of God as in any case settled by revelation. Aquinas considered the Five Ways useful for shared discussion with non-believers; he did not consider them the basis of his own faith.