Summa Theologica The Five Ways

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Summa Theologica

The Five Ways1

by St. Thomas Aquinas

Does God Exist?

Objection 1. It seems that God does not exist: if one of two contraries be infinite, the other would be completely destroyed. But we understand by the term "God" something infinite -namely, something good without limit. Therefore, if God were to exist, we would not find anything bad. But we do find bad things in the world. Therefore, God does not exist.

Objection 2. More sources do not accomplish what fewer sources can. But, supposing that God does not exist, other sources seem capable of accomplish­ing everything evident in the world, since we trace things of nature back to na­ture as their source, and we trace things of free choice back to human reason or will as their source. Therefore, we do not need to posit that God exists.

On the contrary, the Book of Exodus says in the person of God: "I am who am."

I answer that we can prove in five ways that God exists.

The FIRST and more evident way, moreover, is the one we take from mo­tion, for it is sure and evident to the senses that some things in this world are moved. But everything moved is moved by something else. For an object is only moved insofar as it has potentiality for that to which it is moved, while some­thing produces motion only insofar as it is actual. To move something, certainly, is only to bring it from potentiality to actuality, and only an actual being can bring something to actuality. For example, something actually hot, like fire, causes wood, which is potentially hot, to be actually hot, and thereby moves and changes the wood. The same object, however, cannot at the same time be actual and potential in the same respect but only in different respects; for example, something actually hot cannot at the same time be potentially hot, although it is at the same time potentially cold. Nothing, therefore, can produce and undergo motion, or move itself, in the same respect and in the same way. Everything that is moved, therefore, needs to be moved by something else. Therefore, if the cause of a motion is moved, the cause itself needs to be moved by another, and that other by another. But this regress ought not to be endless, because there would thus be no first cause of motion and so no other cause of motion, since second causes produce motion only because the first cause moves them. A stick, for example, only causes motion because a hand moves it. Therefore, we need to arrive at a first cause of motion, one that is moved by nothing else, and all un­derstand this first cause of motion to be God.

The SECOND WAY is by considering efficient causes. For we find that there is an order of efficient causes in the case of those sensible" objects, and yet we do not find, nor can we, that anything is the efficient cause of its very self, because such a thing would thus pre-exist itself, and this is impossible. But we cannot regress endlessly in the matter of efficient causes. This is so because, in all or­dered efficient causes, something first causes something intermediate, and something intermediate causes something last, whether the intermediate things be several or only one. But the effect is taken away if its cause is taken away. Therefore, there will be nothing intermediate or last if there be nothing first in the case of efficient causes. But if we should regress endlessly in the case of effi­cient causes, there will be no first efficient cause, and there will thus be neither a final effect nor intermediate efficient causes, and this is clearly false. Therefore, we need to posit a first efficient cause, and all call this cause God.

We take the THIRD WAY from the possible and the necessary, and the argu­ment proceeds as follows. We certainly find in reality kinds of things that can ex­ist and can not-exist, since we find that certain things come to be and pass away, and so can exist and can not-exist. But it is impossible that all such things always exist, because what can not-exist, at some point of time does not exist. Therefore, if everything can not-exist, there was a time when nothing really existed. But if this is so, nothing would also now exist, because something nonexistent begins to exist only through the agency of something that does exist. Therefore, if noth­ing existed, nothing could begin to exist, and so nothing would now exist, and this conclusion is obviously false. Therefore, not every being is something that can not-exist, but there needs to be something necessary in reality. But every­thing necessary either has or does not have the ground of its necessity from another source. There cannot, however, be an endless regress in the case of nec­essary things that have the ground of their necessity in another source, just as there cannot be an endless regress in the case of efficient causes, as I have shown. We need, therefore, to posit something that is intrinsically necessary, that does not have the ground of its necessity from another source, but which causes other things to be necessary, and all call this intrinsically necessary being God.

We take the FOURTH WAY from the gradations that we find in reality. For we find in reality things that are more good and less good, more true and less true, more excellent and less excellent, and similarly in the case of other such things. But we say "more" and "less" about different things as they in various ways ap­proximate what is most; for example, an object is hotter if it more approximates what is hottest. Therefore, there is something that is most true and most good and most excellent, and so being in the highest degree, for things that are most true, are beings in the highest degree, as the Metaphysics says.''- What we call most in a genus,1013 moreover, causes everything belonging to that genus; for ex­ample, fire, which is hottest, causes everything hot, as the same work says.'' Therefore, there exists something that causes the existing and the goodness and whatever perfection of every being, and we call this cause God.

We take the FIFTH WAY from the governance of things. For we see that cer­tain things that lack knowledge - namely, natural material substances - act for the sake of an end." And this is evident because they always or more frequently act in the same way in order to achieve what is best, and hence it is evident that they reach their goal by striving, not by chance. But things that lack knowledge, do not strive for goals unless a being with knowledge and intelligence directs them, as, for example, an archer aims an arrow. Therefore, there is a being with intelligence who orders all the things of nature to their ends, and we call this being God.

Reply to Objection 1. As Augustine says in his Enchiridion, "Because God is the highest good, he would in no way allow anything bad to exist in his works were he not so all-powerful and good as to act well even with respect to what is bad."', It belongs to the infinite goodness of God, therefore, to permit bad things and to bring forth good things from them.

Reply to Objection 2. We also need to trace things produced by nature back to God as their first cause, because nature, by reason of its fixed end, acts at the di­rection of a higher efficient cause. Likewise, we need to trace even things done by free choice back to a higher cause that is not the reason and will of human be­ings, since things done by free choice can change and fall short. We indeed need to trace everything that can change and fall short, back to a first source that can­not change and is intrinsically necessary, as I have shown.

1 Edited by Stephen Stich for Philosophy 104. The text is in the public domain.

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