Aquinas the Great — Part I


“Aquinas the Great?” That sounds rather pretentious, doesn’t it? Thomas Aquinas was a rather bookish college professor. He taught at the University of Paris during the 13th Century.
Please forgive me for the inappropriate drama. But that introduction is most fitting. Why? Ask a Christian theologian to list the ten most influential Christian thinkers of all times. The apostle Paul probably would be on everybody’s list. But many lists would include the name Thomas Aquinas. Aquinas was unmatched in the depth and breadth of his works.
His most famous work is Summa Theologica. It is an impressive set of books. The word “summa” describes a work that “sums up” knowledge in a field of study. Summa Theologica sums up Scholastic Christian theology in the 13th Century.
The form of these proofs comes from Scholasticism. This also applies to the content and scope of the subject. Many of the topics are not studied by the average seminary student today. That’s sad. Some of Aquinas’ proofs should be common knowledge for Christian leaders. This is particularly true for his proofs for the existence of God.
Aquinas’ proofs also are unknown to the average Christian. Does the average Christian even know there are logical proofs of God’s existence? Probably not. Does it matter? Yes, absolutely! These proofs strengthen the Christian in his daily battle with the Enemy. Armed with these philosophical proofs he is more able to stand in the evil day. (See Ephesians 6: 10-18)
Aquinas begins his Summa by examining the existence of God. His proofs are philosophical. They are based on reason and natural theology. He also quotes a lot of the Bible to support his insights. But few of his insights are new. As a Scholastic he builds on the work of earlier thinkers, especially Aristotle.

Is God’s Existence Self-Evident?

Summa Theologica, First Part, Question 2, Article 1

Isn’t this just like a philosopher? They take simple ideas and make them hard to understand. Why do philosophers make up such fancy words? Are they trying to confuse us? Not really.
Let’s be fair. These special terms are important. Yes, they are technical. But they help philosophers define complex and abstract ideas with precision. Philosophers use fancy words the way physicists use fancy mathematical formulas.
Physicists use their fancy formulas as they attempt to discover new avenues of mathematical truth. They also use their formulas to build up and strengthen realms of established truth. Those complex mathematical formulas confuse me. Likewise, complex terms in philosophy are confusing. Trust me. Philosophers really don’t use them to confuse or impress us. Neither do physicists.
Here it is, our first complex word in this essay–“self-evident.” This word is not difficult to understand. Its meaning is similar to the word “obvious.” For example, try walking outside at noon on a sunny day. Look up into the sky. Can you see the sun? Of course. Obviously! The presence of the sun in the sky at noon on a sunny day is self-evident.
Aquinas states God’s existence is self-evident. It is obvious. God exists! Nature implants this idea within us.

Therefore I say that this proposition, “God exists,” of itself is self-evident, . . . To know that God exists in a general and confused way is implanted in us by nature.

This statement agrees with the apostle Paul. God makes His existence known to us through nature. In Romans 1: 18-20, Paul wrote:

For the wrath of God is revealed from heaven against all ungodliness and unrighteousness of men who suppress the truth in unrighteousness, because that which is known about God is evident within them; for God made it evident to them. For since the creation of the world His invisible attributes, His eternal power and divine nature, have been clearly seen, being understood through what has been made, so that they are without excuse. (NAS)

God is

God reveals Himself in nature

Nature confirms God’s existence. It also displays some of His attributes. For example, the size and power of the universe demonstrates God’s awesome might. Imagine a God powerful enough to create the universe!
The universe also is based on scientific laws. God desires order and structure. God maintains complex movements of planets and galaxies. God’s laws extend to the intricate order of atoms and tiny molecules. God holds the atoms together (Colossians 1: 17). He keeps the universe running in perfect order.
God’s wisdom and intelligence are awesome beyond belief! God takes atoms and molecules. He puts them together in inconceivably complex combinations. He arranges inert molecules in ways that can sustain life! Not only that, some of His complex combinations can think and become conscious of their own being. What sort of God is capable of such sophisticated science? How great is our God! He is worthy of praise!
Nature shouts, “God exists.” Nature can show us some of God’s attributes: power, order, wisdom. But nature has difficulty showing us God’s essence–His personality. That is the role of revelation. The existence of God, however, is self-evident via nature.
Aquinas proceeds. He gathers five philosophical proofs for the existence of God.

The Five Proofs for the Existence of God

Summa Theologica, First Part, Question 2, Article 3

Thomas Aquinas shared five proofs for the existence of God. He did not invent these proofs. The proof from motion, for example, was developed by Aristotle and Plato. But the presentation of the proofs shows the scope of Christian thought by the time of Aquinas.


1. The Proof from Motion

Aristotle had a great influence on Aquinas. Thus, Aquinas submits Aristotle’s Cosmological Argument as the first proof for God. No surprise. According to Aquinas,

. . . whatever is in motion must be put in motion by another. If that by which it is put in motion be itself put in motion, then this also must needs be put in motion by another, and that by another again. But this cannot go on to infinity, because then there would be no first mover, and, consequently, no other mover; seeing that subsequent movers move only inasmuch as they are put in motion by the first mover . . . Therefore it is necessary to arrive at a first mover, put in motion by no other; and this everyone understands to be God.

Hard to understand? That explanation confuses me. Aquinas says one motion is caused by a prior motion. Nothing finite can start its own motion.
“That’s not true,” a friend of mine once said. “Watch closely,” he continued. He put a ball in his hand. Then he held his hand completely still. “My hand and arm are not in motion,” he observed. Then he threw the ball. “See,” he concluded, “my hand was not in motion but it was able to put the ball in motion. Aristotle (and Aquinas) are wrong!”
Let’s look more closely. Yes, he was holding his hand still. Then motion seemed to start from his hand! Was this finite object able to start motion on its own?
Not really. The motion of his hand was preceded by many other motions. Blood moved through his bloodstream. This provided energy to his muscles. Neurons in his brain fired nerve impulses. These nerve impulses surged down his nerves. They gave commands to his muscles. The muscles moved. The movement of the muscles and the movement of the ball were produced by several kinds of prior motion.
Every motion is the result of prior motion. This chain of motion goes back as far as was can know. But does it go back to infinity? We already know the finite cannot produce infinity. No, the chain of motion cannot start from a finite beginning. An infinite being must have produced the first motion.
As Aquinas wrote, “Everyone understands this to be God.”

2. The Nature of Efficient Cause

What is an efficient cause? Did you ever hear anyone use that phrase in a sentence? It seems to be, at first glance, another of those confusing phrases used by philosophers. Well, the phrase is used by philosophers. But it is not really confusing. Here’s an example of an efficient cause.
Did you ever watch a detective show on television? Imagine the first scene. It’s the back patio of a gorgeous house somewhere in southern California. There is a swimming pool. It is surrounded by statuary and police officers. You look again. Yellow crime scene tape cordons off an area around the pool. Then you see a body. A dead person hangs half in, half out of the swimming pool.

Efficient cause

What was the efficient cause of this?

How did this happen? What caused this man to die? Heart attack? Seizure during a swim? Or was it . . .murder? What caused him to die? In other words, what was the efficient cause of his death?
The police officers begin to collect and examine the evidence. There is blood in the swimming pool. More blood collects on the side of the pool. The body is examined more closely. There is a bullet-hole in the center of the man’s chest. The coroner’s report finds a bullet in the man. It pierced his heart. The report concludes the bullet through the heart was the immediate cause of death – the efficient cause.
An effect cannot cause itself. Aquinas begins by stating the obvious: “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.” I cannot cause myself to exist. Someone has to cause me to come into existence. Aquinas continues:

Now in efficient causes it is not possible to go on to infinity . . . 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.

In time and space there cannot be an infinite number of prior causes. Sooner or later there must be a first cause. Aquinas says, “Therefore it is necessary to admit a first efficient cause, to which everyone gives the name of God.”

3. Possibility and Necessity

Here is another proof that is rather obscure today. It’s not obscure because it no longer is true. It’s not obscure because it is hard to understand. It is obscure because we don’t think these sorts of thoughts any more. At least not very often. What is Aquinas saying?
Things exist. That’s certainly true. It is possible for things not to exist. We can see that’s true. Everything in our world decays. It’s possible for everything in our finite world not to exist. Aquinas wrote,

We find in nature things that are possible to be and not to be, since they are found to be generated, and to corrupt, and consequently, they are possible to be and not to be.

It is possible for finite things not to exist. That’s the definition of finite. So it’s possible there was a time when nothing finite existed. If there was a time when no finite thing existed, then nothing finite now would exist unless an infinite thing was involved.

But it is impossible for these always to exist, for that which is possible not to be at some time is not. Therefore, if everything is possible not to be, then at one time there could have been nothing in existence. Now if this were true, even now there would be nothing in existence, because that which does not exist only begins to exist by something already existing.

All of us are possible beings. The entire universe and everything in it has a possible existence. We all are finite. That is, the universe, you and me, at one time did not exist. So something had to exist from eternity. Otherwise, we would not exist. The universe would not exist. Aquinas wrote:

Therefore we cannot but postulate the existence of some being having of itself its own necessity, and not receiving it from another, but rather causing in others their necessity. This all men speak of as God.

Jesus also claims that this necessary being is God the Father. In John 5: 26, Jesus says, For just as the Father has life in Himself, even so He gave to the Son also to have life in Himself” According to Jesus Christ, God the Father is a necessary being. And, as a necessary being, God must be eternal.

Finally . . .

These are the first three proofs gathered by Aquinas. They were important proofs in Aquinas’ time. These proofs remain powerful today. The first three are proofs from logic. The fourth indicates a transcendental knowledge of perfection. The final proof is based on observation of the material world.


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