Friday, March 29, AD 2024 8:19am

Saint Thomas Aquinas and the Existence of God

 

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.

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.

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.

The fourth way is taken from the gradation to be found in things. Among beings there are some more and some less good, true, noble and the like. But “more” and “less” are predicated of different things, according as they resemble in their different ways something which is the maximum, as a thing is said to be hotter according as it more nearly resembles that which is hottest; so that there is something which is truest, something best, something noblest and, consequently, something which is uttermost being; for those things that are greatest in truth are greatest in being, as it is written in Metaph. ii. Now the maximum in any genus is the cause of all in that genus; as fire, which is the maximum heat, is the cause of all hot things. Therefore there must also be something which is to all beings the cause of their being, goodness, and every other perfection; and this we call God.

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.

 

 

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Michael Dowd
Michael Dowd
Thursday, January 28, AD 2021 6:25am

What a great and needed program, especially now, is the ‘Meeting of Minds’. Thanks for bringing it to our attention–again in some cases.

Pinky
Pinky
Thursday, January 28, AD 2021 9:47am

It always seemed to me that the first two proofs are saying the same thing. I find them unassailable, though. The third isn’t quite as strong, and the fourth requires a set of previous assumptions that I’m sure Aquinas worked out elsewhere, but aren’t stated here. The fifth is the one that every atheist goes after, and I wouldn’t consider it a proof.

Rudolph Harrier
Rudolph Harrier
Thursday, January 28, AD 2021 1:19pm

Second proof refers to efficient causes only. First proof refers to all motion (i.e. change from potentiality to actuality). Probably easier to read it in modern language as a proof regarding “change”. So it involves all changes, including those relating to formal, material or final causes. For example a change in a person’s will may not have an efficient cause as such, but is still a motion (and in Aquinas’s framework even this change requires cooperation from God).

None of the arguments as presented in their common forms here are complete. This is because they are presented early in the Summa Theologica, where Aquinas’s primary concern is answering the questions “Is God’s existence knowable through reason (i.e. apart from revelation) and is it self evident?” Since the Summa Theologica (in contrast to say the Summa Contra Gentiles) is meant for a Christian audience, Aquinas is not trying to actually convince people in these words that God exists. (This is also why he doesn’t expand on why the unmoved mover, etc. is understood to be God). Instead he is attacking too positions that other Christians of his time did take: first, that we can’t know about God apart from scripture and revelation, second that God’s existence is self-evident and cannot be denied (he explicitly responds to Anselm’s argument for this in an earlier article). To defeat both of these positions Aquinas needs to show arguments for God’s existence which require actual reasoning, i.e. which are not self evident. So he gives summaries here but as he isn’t actually expecting his reader to disagree with the proposition “God exists” he does not expand upon them.

Note that in the Summa Contra Gentiles, where his expected audience is not Christian, he not only gives a longer form of some of the arguments presented here, but he also explains why the being discovered must be eternal, simple, incorporeal, Existence itself, entirely necessary, universal perfection, etc. At that point indeed it would be understood that what we are talking about is God.

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