Thomas Aquinas · Theology

The Five Ways

Aquinas’s five arguments that the existence of God can be demonstrated by reason alone, working up from the ordinary facts of the world.

From the lesson

Thomas Aquinas, the great thirteenth-century theologian, believed something many find surprising: that the existence of God is not merely an article of faith but can be demonstrated by reason, starting from ordinary facts anyone can observe about the world. In his vast Summa Theologica, he offered five such arguments - the quinque viae, or ‘Five Ways.’ Each begins not with scripture but with a plain feature of reality, and reasons its way to a first principle that, Aquinas says, ‘everyone understands to be God.’

Aquinas calls the argument from motion ‘the first and more manifest way.’ Its steps are simple. Some things are in motion (where ‘motion’ means any change - a cold thing becoming hot, a potential becoming actual). Nothing moves itself; whatever is moved is moved by another. But this series of movers cannot go back to infinity, for then there would be no first mover, and so no motion at all - like a train of carriages with no engine. Therefore there must be a first mover, moved by nothing else.

Briefly, the five: the First Way argues from motion to an unmoved mover. The Second Way argues from chains of cause and effect to a first efficient cause. The Third Way argues from the fact that things come into and go out of existence (they are ‘contingent’) to a being that exists necessarily. The Fourth Way argues from the degrees of goodness, truth, and nobility we observe to a maximum that is their source. The Fifth Way argues from the purposeful order of nature to an intelligent designer. Five roads, Aquinas holds, all arriving at the same summit.

This is the opening of the lesson. The rest — the dialogue, the primary source, and the recall — is in the app.

What you'll be able to recall

You learned that the Five Ways argue from features of the world up to God. Reconstruct the shared structure of the arguments, and state the strongest objection to them, in your own words.

Leads to Immanuel Kant.

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