The Five Ways

St. Thomas Aquinas's five demonstrations of the existence of God.

St. Thomas offered Five Ways to demonstrate God's existence.

They do not rest on faith or Scripture; each starts from a plain feature of the world and reasons its way to the source that must lie behind it.

Two simple ideas carry all five ways. The first is the difference between act and potency — what a thing actually is now, versus what it has the potential to become. The second is the difference between essence and existence — what a thing is, versus the fact that it exists at all. Act and potency underlie every way; essence and existence come into their own in the last three.

With those two distinctions in hand, the ways themselves all share the same shape:

1. Notice a feature of reality (things change, or depend on something else to exist).
2. Show that this feature cannot go on explaining itself in an endless chain.
3. Conclude to a first source — and identify it with God.

Expand a section below to walk through each way.