Lesson 5 – What is Efficient Causality?

It is not easy to prove the existence of God by reason alone. Nonetheless, it is possible. And among all of the various “proofs” for God’s existence, perhaps none are more famous than the “Five Ways” of the thirteenth-century philosopher and theologian, Saint Thomas Aquinas.

In this second video, we continue our three-part examination of the “Second Way” in which Aquinas demonstrates the existence of God: the way of efficient causality.

Course Reading

Commentary on Aristotle’s Metaphysics, Bk. V, Lesson 2 | St. Thomas Aquinas

Summa Theologiae I, q. 2, a. 3 | St. Thomas Aquinas

Excerpt from the Summa Theologiae I, q. 2, a. 3:

The second way is from the nature of the efficient cause. In the world of sense we find there is an order of efficient causes. There is no case known (neither is it, indeed, possible) in which a thing is found to be the efficient cause of itself; for so it would be prior to itself, which is impossible. Now in efficient causes it is not possible to go on to infinity, because in all efficient causes following in order, the first is the cause of the intermediate cause, and the intermediate is the cause of the ultimate cause, whether the intermediate cause be several, or only one. Now to take away the cause is to take away the effect. Therefore, if there be no first cause among efficient causes, there will be no ultimate, nor any intermediate cause. But if in efficient causes it is possible to go on to infinity, there will be no first efficient cause, neither will there be an ultimate effect, nor any intermediate efficient causes; all of which is plainly false. Therefore it is necessary to admit a first efficient cause, to which everyone gives the name of God.

Course Listening

Unlocking Divine Action: Causality from Thomas Aquinas to Quantum Mechanics | Fr. Michael Dodds, O.P.

Causality According to the Aristotelian-Thomistic Perspective | Prof. Michael Gorman