Jacques Maritain Center : A First Glance at St. Thomas Aquinas / by Ralph McInerny


That God exists is, for the believer, as plain as the nose on his face. From his mother's knee perhaps he has been taught to call on God, to praise and honor Him, to obey Him. Such talk blended with all the other things he learned as he learned his alphabet and colors and telephone number. The believer is no more likely to doubt the existence of God than of the world. Does this mean that he takes God to be as obvious as the world? Is God really as plain as the nose on his face?

A little reflection on the way he has been taught to think of God will show him this is not so. God has been spoken of as a father, as a judge, as a maker, as a shepherd and mother hen, as thunder and lightning, as a mighty fortress. God is always spoken of as like other things, the things He has made. He never seems to be described in terms proper to Himself.

St. Paul, in his Epistle to the Romans, begins by listing all the crimes and sins of the pagan Romans. This may seem unfair since pagans are not Christians, but Paul goes on. They are without excuse, he says, because they could come to know the invisible things of God from the things He has made. Reading this in her bible, Fifi will believe it, believe it because it has been revealed. What is she believing? That revelation and faith are not necessary to come to knowledge of God and that to know God is to learn the human good and what we should do.

A curious thing. It is a matter of faith that faith is not absolutely necessary to achieve some knowledge of God. Thomas Aquinas no more than Fifi is in need of arguments for the existence of God. He already holds as true the proposition that God exists -- on the basis of faith. But he like many before and after him was prompted by that passage in Paul to formulate proofs of the kind Paul seems to have in mind.

From this angle, we can see what a glorious thing Aristotle's philosophy was for Thomas. In Aristotle were to be found proofs for the existence of God which had been formulated by a man uninfluenced by revelation, Old Testament or new. There are proofs in Augustine, others in Anselm, but these were formulated by men for whom the issue was not in doubt. Aristotle loomed like a laboratory example. We can imagine the excitement with which Thomas pored over those passages in Aristotle where the pagan philosopher argues that the world of change and motion requires in order to be at all -- and he thought it had always been -- a first mover, itself unmoved. A Prime Mover.

The Structure of a Proof

Early in the twelfth century, Anselm of Canterbury -- he was then Abbot of Bec in Normandy -- formulated a proof that Thomas dismissed as little more than a trick. Anselm's proof continues to interest philosophers; indeed, it sometimes seems to be the only proof that interests philosophers. Anselm sought to show that once it got into your head that God is "that than which nothing greater can be thought," you could no longer reasonably deny that God existed.

One could go on and on about this effort (people do) but we are presenting the thought of Thomas Aquinas and he thought very little of Anselm's attempt. I mention it because it so very different from the kinds of proof Thomas did think worked, several of which he found in Aristotle.

Anselm begins with the meaning of "God" and attempts to convince us that the denial of God's existence is incompatible with what "God" means. Now you might say that the meaning Anselm assigns to "God" invokes other things, indeed everything other than God, whatever is less than Him. But all that is involved is that God is greater and they are less. In terms of what? Thinkability. It is all very abstract.

Even if such a proof worked, Thomas would have thought it a bit of a hothouse item, something for experts. The first time we hear it, we have the feeling our leg is being pulled. What it lacks is any obvious attention to the way in which we know and the sorts of things we can lay claim to know.

A proof should move from what is known to what can come to be known on the basis of what is known. The conclusion is true because the premises are true, which is why, in analyzing the proof, in assessing it, we turn to the premises to see if they can bear the freight that is being put upon them. Anselm's proof is really a reductio ad absurdum, the kind of proof that is fitting when doubt is cast on the self-evident. But the existence of God is not self-evident to us, however familiar He may be.

The premises of a proof for the existence of God must be truths about the world. It is from the things that are made that we can come to knowledge of the invisible things of God. That is just what Aristotle's proof looks like. The world is such that the world cannot be all there is. If it is, and it is, there must be a cause of it quite unlike his effect (I speak of the Prime Mover as a person because Aristotle did. One ruler is best, one ruler let there be.)

Why Does the World Need a Cause?

The world is an unwieldy place, it would seem, and one might doubt that we have an idea that matches the term. It seems synonymous with "everything" and what precisely does "everything" mean? If we said that everything has a cause, we would have to be ready to show that to be true of this thing and that thing and the other, on and on, through all the things that are. We could never establish the claim. Isn't a proof of the existence of God from the world going to run into the same difficulty?

Aristotle's proof of the Prime Mover comes at the end of his Physics, a work in which, we remember, he was setting down truths of a high generality about whatever comes to be as the result of a change. He argued that any actuation of the potency of a subject requires an agent who is acting for an end. He also argued that while motion is the act of the moved thing and not of the mover as such, every physical mover is also, in a different respect, being moved by what it moves. Against that background he formulated an argument that can be stated briefly as follows.

Whatever is moved is moved by another.

There cannot be an infinite series of moved movers.

There must be a first unmoved mover.

It is unfair to the proof to make it look as if those three sentences in isolation are all it takes. The proof is dependent on everything that has preceded it in the Physics. But I provide it in the short form because that is what Thomas himself does. This is the first of the five ways of proving God exists that he sets down in a famous text. A glance at the premises will convince you that these are far from self-evident truths. They must in turn be proved.

The Nerve of the Proofs

It is the second premise that may seem most dubious to you, just on the face of it. If we think of a series of things such that A is caused by B and B by C by C by D and D by. . ..Just keep going. Why not? If A can be explained by invoking B, and B by invoking C, you can just keep it up, going on forever, and everything will be explained without any need to bring in God, that is, a cause different from the ones that are already doing a good job. Remembering earlier remarks about the eternity of the world, you could add that this is just what Aristotle seems to assume. Eternity and infinity seem to remove the need for anything different from the things we start with.

This is a familiar kind of negative response to the proofs. The objector will say: if you want something eternal and unexplained, let it be the world, no need to bring in God. He may even in blasphemous exuberance allow that we can call the world 'God' if we need a use for the term.

What is puzzling is that it was precisely Aristotle who, though he held the world to be eternal, formulated the argument for a prime mover. Aristotle was not the village idiot, and we can assume his attention span was at least as great as ours. It wasn't that he forgot about claiming the world is eternal. That is an ingredient of the proof he is formulating. Chances are that the objector is missing something in Aristotle's effort. What could it be?

To explain A by B and B by C and C by D, and so on to infinity, does not explain why there are things of that kind. Given that there are such things, they can bring about other things like themselves, and carry on to a faretheewell, but Aristotle saw that if a thing could cause another thing of the same kind as itself, it could not be the cause of the kind of thing they both were. Why are there any things like that at all? To say that this one causes that one and that one another, does not address that question. That seems to be the reason why Aristotle, who thought the world had always been, did not think that a world containing only things that came to be as the result of a change could be all there was. There had to be at least one other cause, a cause of a different kind. An uncaused cause. God.

Some Other Puzzles

In a primer like this we can now pass blithely on. I need not repeat that this matter, like all the others discussed in one little handbook, needs much further elaboration. But we are introducing Thomas, not exhausting him.

Thomas did not think proofs of God's existence are easy. He noted that Aristotle maintained that they are the culminating concern of the philosopher, something possible only in wise and ripe old age. It is the rare bird who can formulate a sound proof of God's existence. It is much easier to formulate objections to them. We should not think that Thomas took St. Paul to be saying that it was the work of an afternoon to acquire conviction that God exists.

This provided him with the answer to one question that was bound to arise. Why does God reveal to us that He exists if we can come to know Him by using our minds? Because few would arrive at such knowledge and those who did would reach the goal late in life. But that God exists if of great moment for how we live our lives, early and late. So God in His mercy, revealed himself to us.

Early on we mentioned the distinction Thomas makes in the things that have been revealed between the mysteries of faith (which can only be believed) and the preambles (which are in principle knowable). That God exists is the most basic preamble of faith. Thomas at first believed and then came to know that God can be known from the world; men can know He exists and some of His characteristics. This enabled Thomas to formulate the following argument.

The argument addresses another question Thomas put himself. Is it reasonable to give one's assent to truths he cannot understand? The mysteries of faith -- the Trinity, the Incarnation and the like -- cannot be known to be true in this life. Only on the basis of the gift of faith do we give our assent to these truths. Is this reasonable?

Here is the argument Thomas gives on behalf of an affirmative answer. If some of the things God has proposed for our belief can be known to be true, it is reasonable to accept the others as true. The preambles thus provide reasonable grounds for accepting the mysteries. Not that the mysteries are thereby proved to be true, of course. The argument is on behalf of the reasonableness of believing them.


Can God's Existence Be Proved?

There are two kinds of demonstration, one by way of the cause, which is called propter quid, and this from what is first simply speaking, another by way of effects which is called a quia demonstration, which is from what is first for us. For when an effect is more obvious to us than its cause, we proceed from the effect to knowledge of the cause. From any effect the existence of its proper cause can be demonstrated (if its effects are more obvious to us), since the effect depends on the cause, given the effect, the cause must exist. That God is, since this is not self-evident to us, is demonstrable through his known effects.

That God exists and other like things which can be known of God through natural reason, as is pointed out in Romans 1:19, are not articles of faith but preambles to the articles, for faith presupposes natural knowledge as grace presupposes natural knowledge as grace presupposes nature and perfection the perfectable. Nothing prevents someone from accepting on faith what in itself is demonstrable and knowable if he does not understand the proof.

-- Summa theologiae, First Part, Question 2, article 2

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