Good evening,

Please can you explain to me why Aristotle and St. Thomas, in their demonstration of God, say that the backward causal chain cannot be endless, but there must necessarily be a starting point which is God?

I don’t understand why it “can’t”.

Who says that?

On what basis “cannot”?

Seen like this, it seems to me like a bit of a double-cross, like “to close the discussion I’ll insert God and close the chain”.

I mean: as it is normally explained and described, it is not clear why the causal chain cannot be eternal.

Who forbids it?

Thank you.

Priest’s answer

Dear friend,

1. why we cannot go to infinity is clear and perhaps too clear, so much so that St. Thomas does not explain it.

I confess that I too asked myself this question at the time.

The answer, however, is not difficult: because everyone would communicate an input that they do not possess themselves and that they have not received.

In other words, the moment in which what moves passes from potency to act and could communicate this energy to an infinite series of beings would be missing.

If it moves, that is, it passes from potency to act, it moves because ultimately it is moved by a reality which in itself is act.

If it was act, without power, it would be God and then he would already have every perfection in himself.

For this reason Aristotle, speaking of God, said that God is pure Act, an immobile Mover, he moves without being moved, without passing from potency to act.

This reasoning corresponds to the so-called first way of St. Thomas.

2. But here are the words of St. Thomas himself.

If you read them carefully, you will see that there is no illogical passage in them.

“The existence of God can be proved in five ways.

The first and more manifest way is the argument from motion. It is certain, and evident to our senses, that in the world some things are in motion. Now whatever is in motion is put in motion by another, for nothing can be in motion except it is in potentiality to that towards which it is in motion; whereas a thing moves inasmuch as it is in act. For motion is nothing else than the reduction of something from potentiality to actuality. But nothing can be reduced from potentiality to actuality, except by something in a state of actuality. Thus that which is actually hot, as fire, makes wood, which is potentially hot, to be actually hot, and thereby moves and changes it. Now it is not possible that the same thing should be at once in actuality and potentiality in the same respect, but only in different respects. For what is actually hot cannot simultaneously be potentially hot; but it is simultaneously potentially cold. It is therefore impossible that in the same respect and in the same way a thing should be both mover and moved, i.e. that it should move itself. Therefore, 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; as the staff moves only because it is put in motion by the hand. Therefore it is necessary to arrive at a first mover, put in motion by no other; and this everyone understands to be God”. (Summa theologica, I, 2, 3).

3. Coming to the third way: St. Thomas notes that there are many realities that do not have the source of existence within themselves because they might not even exist.

In fact, if they had the source of existence within themselves they would have existed always and forever. And they would coincide with God.

But this is not the case.

Therefore, if they exist while they might not exist, it means that they have received existence from a being different from them, which in itself is the source of existence, which exists in itself. And this is the one we call God.

If we could go to infinity we would find ourselves faced with a series of beings who do not have the source of existence within themselves, and yet communicate it to each other without having received it. And this is evidently impossible because nothing comes out of nothing.

Only a creative power, which is God’s own, can do such a thing.

4. Here too here are the precise words of St. Thomas: “The third way is taken from possibility and necessity, and runs thus. 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. 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. Therefore, if at one time nothing was in existence, it would have been impossible for anything to have begun to exist; and thus even now nothing would be in existence — which is absurd. Therefore, not all beings are merely possible, but there must exist something the existence of which is necessary. But every necessary thing either has its necessity caused by another, or not. Now it is impossible to go on to infinity in necessary things which have their necessity caused by another, as has been already proved in regard to efficient causes. 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.” (Ib.).

5. And here is the fifth way: “The fifth way is taken from the governance of the world. We see that things which lack intelligence, such as natural bodies, act for an end, and this is evident from their acting always, or nearly always, in the same way, so as to obtain the best result. Hence it is plain that not fortuitously, but designedly, do they achieve their end. Now whatever lacks intelligence cannot move towards an end, unless it be directed by some being endowed with knowledge and intelligence; as the arrow is shot to its mark by the archer. Therefore some intelligent being exists by whom all natural things are directed to their end; and this being we call God.” (Ib.).

6. As you can see, it is not a question of closing a discussion without reasoning.

But precisely through reasoning, we arrive at the cause from the effects.

Ultimately it is the same procedure used by Saint Paul, who in the letter to the Romans writes: “Ever since the creation of the world, his invisible attributes of eternal power and divinity have been able to be understood and perceived in what he has made.. ( Rm1,20).

I bless you, I wish you all the best and I remember you in prayer.

Father Angelo

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