St. Thomas Aquinas' Five Proofs of God

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  • 0:57 Motion
  • 1:38 Causality
  • 2:27 Contingency vs. Necessity
  • 3:42 Perfection
  • 5:04 Design
  • 5:58 Lesson Summary
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Lesson Transcript
Instructor: Jessica Whittemore

Jessica has taught junior high history and college seminar courses. She has a master's degree in education.

This lesson will explore Thomas Aquinas' 'Summa Theologica'. In doing so, it will specifically highlight Aquinas' Five Proofs for the existence of God.


Some things never change. Boys' locker rooms always stink. French fries go with hamburgers. Turkeys die at Thanksgiving. Philosophers argue about the existence of God.

Since there's not much more to say about French fries or turkeys, and since I haven't spent much time in a boys' locker room, we'll spend today looking at the God argument. More specifically, we're going to look at the famous Thomas Aquinas and his Five Proofs for the existence of God.

For starters, Thomas Aquinas was a 13th-century philosopher who wrote Summa Theologica. Considered one of the most important pieces of Western literature, this work contains Aquinas' Five Proofs for the existence of God. Also referred to as the five ways, these proofs are still alive and kicking in the conversations of modern philosophers.

Due to their importance, let's take a look at each proof. As we do this, keep in mind that different sources tend to title these proofs a bit differently. However, their meanings remain the same.


Proof one: The Proof of Motion

Stated very simply, the proof of motion says something in motion had to be set in motion. In other words, if something is moving, someone or something had to move it. For instance, a car moves because a foot pushes the gas. However, who pushes the foot? Of course, the person attached to the foot does. But who pushes the person who pushes the foot, which pushes the car? On a grander scale, who pushes the Earth, which moves the person, who pushes the foot, which pushes the car?

Aquinas' firm answer is God. God is the first and ultimate mover. Motion is proof that He exists!


Proof two is the Proof of Causality.

Sort of similar to the Proof of Motion, the Proof of Causality argues that everything that is has been made. Stated a bit differently, someone caused it to come into being. Yes, some things have lots of makers, but ultimately there must be one supreme maker who made all the other makers!

For instance, take a look at jelly. Jelly is made from fruit and sugar. Some farmer somewhere planted some seeds to get sugar cane and strawberries, but who made the seeds? Even more of a question, who made the farmer? Likewise, air is made up of oxygen and nitrogen, but who made up these elements? We're made up of water and goo, but who made us?

Again, Aquinas boldly answered - God. God is the first and ultimate maker. He has caused it all!

Contingency vs. Necessity

Moving on, proof three is the Proof of Contingency vs. Necessity.

Now, this one is a bit of a rollercoaster ride, so hold on. Also called the Proof from Necessary vs. Possible Being, this one espouses that something can't come from nothing. It is necessary to have one necessary being! Like I said, this one's a bit tricky.

Let's come at it with some examples. We'll start with a bird. A bird is a pleasant-looking thing, but it's really not necessary. A bird can fall from a tree or get hit by a car and the world will not come to an end. My daughter will cry, but the Earth will keep spinning. In short, the bird is not necessary. It has a beginning. It has an end, and life is not contingent upon either!

A bit more sobering, the same can be said for each of us. We have a beginning, and we will have an end. Yes, people will mourn. However, when we say goodbye to this Earth, it will keep orbiting. The spinning of the planets is not contingent upon us.

Based on this, Aquinas asserted there must be one ultimate power that is necessary. There must be one being who keeps all of us contingent beings chugging along. Again, his answer is God. God is the one necessary being in the midst of all us contingent ones.


Proof four is the Proof of Perfection.

This one is a bit easier to understand, but before I give its definition, I have an exercise for us. Please take out a piece of paper and draw a scale from one to ten. I'll give you some time.

Mark one as evil and ten as perfect. Now, place Hitler and Mother Theresa on your scale. Don't over think it; just put them down.

Now, here's my scale. Compare it to yours. Although we've never met, I'm guessing our scales look a lot alike. I'm guessing you placed Hitler toward the very bottom and Mother Theresa toward the top.

Proof of Perfection Scale

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