Summa Theologiae
PART 4
The Summa Theologiae of St. Thomas Aquinas is justly one of the famous works of Christendom. Yet this book, meant for beginners in the ages of Faith, can seem overwhelming today. We give here an introduction to the Summa by Fr. Albert, a son of St. Dominic, in the hope of making this important work more accessible to modern readers.
THE FIVE WAYS
St. Thomas gives five ways to prove the existence of God.
1) The most manifest way: the argument from motion
The argument may be summarized as follows. We see in the world things that are in motion (“motion” here is to be taken not just for local motion, but for change in general). Whatever is in motion is moved by another, and if this other is also in motion, it must, then, be moved by still another. This series cannot go on forever but must end at a mover that is not in motion because otherwise there would be no motion at all. This first mover that is not put in motion by any other is what everyone understands to be God.
The logic of this argument is evidently sound. To prove its truth we have to justify two principles. The first, and most important, is the statement: “Whatever is in motion is moved by another” (omne quod movetur ab alio movetur). Let us first read the justification of this key principle given by St. Thomas himself, which is based on the impossibility of something being simultaneously in potentiality and in act with respect to the same thing:
Whatever is in motion is put in motion by another, for nothing can be in motion except in so far as it is in potentiality to that towards which it is in motion; whereas a thing moves inasmuch as it is in act. For to move is nothing else than to raise something from potentiality to actuality. But nothing can be raised 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.
What is moved, then, is necessarily in potentiality to the term of its movement, that is, it can become what it is going to become but it isn’t yet. Therefore it cannot be the cause of its own becoming what it isn’t yet, because what does that has to be in act with regard to this term: only what is hot can make something that is not hot become hot. So whatever moves has to be in act and what is moved has to be in potentiality and therefore what moves can’t be what is moved.
John of St. Thomas explains the same principle thus:
Nothing is raised to actuality by what is in potentiality, but rather by what is in act : for potentiality does not have the power to raise but rather to receive. Therefore what moves must be in act and what is moved must be in potentiality. It is impossible, however, that something be simultaneously in act and in potentiality with respect to the same thing, that it be the mover and the moved, because actuality and potentiality imply contradictory properties. For what is in potentiality to something does not possess it; but what is in act possesses it, or something that is even higher than it, by reason of which it is no longer in potentiality but in act. Therefore the same thing cannot be simultaneously in potentiality and act with regard to the same thing; therefore neither can it simultaneously move itself and be moved; therefore if it is in motion, it is moved by another, for what is in motion must be passive and depend on what moves it actively; therefore if it is not in motion from itself then it must be so by another.
All this might seem like beating a dead horse since it all seems so obvious, and yet it is necessary to beat this horse until it is most certainly dead for all the proofs of the existence of God depend precisely on these obvious principles which many people, nonetheless, implicitly deny when they deny the existence of God.
The second principle of St. Thomas’ argument is equally clear, namely: “A series of movers which move must ultimately end at a mover that is unmoved.” St. Thomas proves it, starting from a restatement of the first principle that he has just established, and then concludes directly at God’s existence.
Therefore, whatever is in motion must be put in motion by another. If that by which it is put in motion be itself 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.
2) The second way, from the nature of the efficient cause
The point of the departure of the second proof, which is closely parallel to the first one, delves deeper into the world of sense that surrounds us, going beyond the simple fact of the movement or becoming of things to their being; which is the termination of their becoming and remains after it. Something can be the cause of the becoming of an effect without being the cause of its being, as in the case, for example, of a father who caused the becoming of his son but does not cause his being, which continues along just fine even after the father has died. The causes of the being of a thing exercise an immediate and present influence on it in such a way that the thing could not continue to be without them. Without the heat of the sun and the atmospheric pressure exercised by the air, for example, all animals would very soon cease to exist, as they would also if the chemical activity of oxygen in their lungs ceased to operate. All these cosmic agents are so many causes of the being of these animals and thus are called by St. Thomas “efficient causes” whose influence is exercised on the deeper level of being as opposed to the more superficial activity of mere causes of motion.
Starting from what he calls this “order of efficient causes,” that is, the fact that we see in the world around us that things depend for their being on other things, St. Thomas argues that the existence of these effects necessarily implies the existence of their causes, for, he says:
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 if these causes are themselves caused, then we must for the same reason postulate the existence of their causes too, and finally come to a cause that is not caused, for just as the series of causes of motion cannot be infinite, for otherwise there would be no motion, similarly the series of causes of being cannot be infinite or there would be no being. Garrigou-Lagrange draws the final conclusion of this second argument, saying:
We are thus led to the source of being, to a supreme efficient cause, which has no need of being caused nor of being preserved in existence.…The Being a se, the Supreme Being, which is the direct cause not of some mode of being (such as heat or light), but of being as such, is the cause of everything which is not its own cause, and it can be the cause of everything that is capable of existing. The Being a se endows everything with reality and is the direct cause of being; just as fire is of heat, and light of illumination; it can endow with reality all things which do not involve a contradiction, just as fire can heat all things which are capable fo being heated.
3) The third way, from possibility and necessity
In the world we see things that can be and not be, since they are found to be generated and to corrupt. If they can be or not be, they must have their being from somewhere other than themselves (because if they had it from themselves then they could not not be). Now this source of their being must not itself be susceptible of not being, because then it would just be part of this same group of beings that is susceptible of not being and so could not be the principle that accounts for them. However, if this source that is not susceptible of not being doesn’t have this from itself, then it must have it from another, and if this other doesn’t have it from itself, it must have it from yet another, and so on. But this passing of the buck cannot go on indefinitely, it must sooner or later arrive at something that does not receive its non-susceptibility of not being but has it from itself, a being that is absolutely necessary, and this is what all call God.
The key to this argument is the statement that everything cannot be just possible (what is suceptible of not being), but the possible absolutely requires as its cause that which is necessary (what cannot not be). Garrigou-Lagrange explains this in a little more technical language and shows how the argument finally rests on the principle of non-contradiction:
Why is an uncaused contingent being repugnant to reason? It is because a contingent being is that which can either exist or not exist (this being its definition). Therefore it is not self-existent, and must be dependent upon another for this; otherwise, if it were neither self-existent nor dependent upon another for existence, it would bave no reason for existing, and so would be the same as nothing. “Nothing is what results from nothing.” To say that from nothing, or that from no cause either efficient or material, something comes into being, is a contradiction.
St. Thomas himself states the principle much more bluntly, and concludes with a tinge of a smile at the absurdity of where denying it leads:
It is impossible that everything be like this (that is, possibly not existing) because what is susceptible of not being, at some point is not. So if everything were susceptible of not being, then at some point there would be nothing. But if this were true, then there would be nothing now, because what is not does not begin to be except through what is; if, therefore, at one point there were no being, it would be impossible for being to begin to exist and so there would be nothing now, which is obviously false.
4) The fourth way, from the grades of being
This argument takes as its starting point the different grades of the same perfection found in various beings:
Among beings there are some more and some less good, true, noble, and the like.
It must be noted that the perfections spoken of here that are susceptible of different degrees are all what are called “transcendentals.” This term comes from the fact that these perfections “transcend” the fundamental categories of genus and species into which, normally, all beings fit. A dog is a certain particular species and belongs as well to a certain genus, to which genus also belong cats and giraffes, which have, likewise, their own species to themselves. Caninity and felinity are specific perfections that don’t wander outside their fixed borders and neither are they found to be more or less. Something is not more or less a dog: it either is or it isn’t, and the same goes for cats and giraffes.
Transcendentals, however, are exceptions to this rule: they are not confined to one fixed species or genus of being but are found in different categories. There are not only good dogs, but good cats (or at least some people think so: others would say that there is no such thing as a good cat, but this is mere prejudice and not good metaphysics). And there are not only good animals but good plants, good machines, good music, good food and all sorts of other good things. Goodness, then is a transcendental. It exists in different things and means something quite different in each case: what makes a good dog does not make a good cat (which is probably why some people think that there are no good cats, because they want them to be just like dogs, which is ridiculous). Nevertheless, even though goodness concretely means entirely different things, it does have a specific meaning so that different things truly do have goodness in their own different ways. Thus the word “good” is an analagous term, that is to say, it does not have one single meaning but applies differently to different things. And the same thing goes for the words “truth” and “beauty” and “unity” and even “being.”
What interests us presently about these transcendentals is the fact that they are found in different degrees in different things. A self-evident principle, for example, has more truth than the conclusions drawn from it. Similarly the end for which something is done is better than the means which lead to it, or, more concretely, this car is better than that one (Fords are better than Chevies). This painting is more beautiful than that one, this basketball team has more unity than that one, and basketball teams, in general, have less unity than living organisms do.
St. Thomas goes on to say that since there are these degrees of more or less goodness, truth, beauty and unity in things, there must exist something which possesses them in a maximum degree and is the cause of these perfections in everything else that possesses them in a lower degree. Thereupon he immediately concludes:
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.
This principle he uses here, namely, that “the maximum in any genus is the cause of all in that genus” was a commonplace axiom among philosophers, going back all the way to Plato, and so St. Thomas, wanting to brief, justifies it by simply giving a reference to Aristotle. For us novices, however, Garrigou-Lagrange gives an explanation of it which will help us understand. He writes:
When a perfection, the concept of which does not imply any imperfection (which is the case with these transcendentals), is found in various degrees in different beings, none of those which possess it imperfectly contains a sufficient explanation for it, and hence its cause must be sought in a being of a higher order, which is this very perfection.
We can arrive at this conclusion starting from the degrees of perfection in things by two different angles. Firstly, if the same note is found in two beings, neither one of them possess it in their own right, and so it must come to them from another that does so possess it. For example, Phaedo is beautiful, but Phaedrus is too, so beauty doesn’t belong to either of them in and of themselves, they both merely participate in something other than themselves that is beauty itself. The beauty they both have cannot come from themselves because, in themselves, they are different while the beauty they have is common to them both. St. Thomas writes:
If one of some kind is found as a common note in several objects, this must be because some one cause has brought it about in them; for it cannot be that the common note of itself belongs to each thing, since each thing is by its very nature distinct, one from the other, and a diversity of causes produces a diversity of effects.
Phaedo and Phaedrus are different from each other and different from beauty itself, so the explanation for the beauty that is common to them must be something different from themselves. Now if this thing in common that explains their common beauty is not itself beauty itself but something else that merely possesses beauty or participates in it, like Phaedo and Phaedrus, we don’t get any further to finding out where the beauty ultimately comes from. We will just have to say, as we did with Phaedo and Phaedrus, that it has beauty but isn’t the cause of it: it is just a third member of the group of things that shares in beauty but must receive it from outside itself. Finally we must arrive at something that doesn’t just have beauty but is beauty itself, and so doesn’t need to receive it from outside itself and which is the cause of beauty in everything else that has it.
The second angle is to start from the very fact that something possesses a perfection imperfectly, because that necessarily implies that it does not have the perfection of itself but from somewhere else. St. Thomas writes:
Whatever belongs to a thing by its very nature, and has not been caused in it, cannot belong to it in an imperfect manner.
So if it does belong to it in an imperfect manner, it has been caused in it. If goodness is united with non-goodness, that is, if it exists imperfectly, this can only be by an extrinsic cause because, by itself, goodness isn’t united with non-goodness. As St. Thomas, again, puts it:
Things in themselves different cannot unite, unless something causes them to unite.
So where goodness is found imperfectly, it must be received from outside and ultimately from goodness itself.
Whatever a thing may fittingly have, if it does not originate from its nature, accrues to it from an extrinsic cause; for what has no cause is first and immediate. (Contra Gentes, Bk. II, c. XV, n. 2)
What is found in a being without properly belonging to it according to its nature, is something which has been caused in it. In fact, not possessing this characteristic of itself and immediately (per se primo), it can possess the same only in a conditional manner, by reason of another, and, in the final analysis, from another which possesses the same of itself and immediately, as something belonging to its nature (“secundum quod ipsum est”). Wherever there is diversity or composition, it is conditional, until we finally arrive at pure identity. It is only the latter that is capable of self-existence, whose existence originates from its nature, which is to being as A is to A, which is Being itself, or existence itself, ipsum esse subsistens.
5) The fifth way, from the governance of the world
The final proof, and no doubt the most convincing, especially for the popular mind, is exposed by St. Thomas as follows:
We see that things which lack intelligence, such as natural bodies, act for an 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.
As usual, St. Thomas first gives the minor of the argument: things in the world that lack intelligence act for an end. Then he gives the major: things without intelligence cannot act for an end unless they are directed towards that end by an intelligent being. The conclusion naturally follows: there must be an intelligent being that directs them.
St. Thomas himself justifies his minor premiss, that natural things in the world act for an end, saying:
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.
There are two major objections raised against this premiss: the first pretends that things do not act for an end but merely by chance, the second says that they act merely out of necessity.
a) Things do not act merely by chance
Fr. Garrigou-Lagrange, developing St. Thomas’ reasoning, refutes the first objection by showing that it implies the denial of the principle of sufficient reason, that is, the principle that states that it is impossible for something to come from nothing: it must have a cause or a “sufficient reason” to account for it.
What happens always, or nearly always, cannot possibly be the result of chance. This constancy would be without a sufficient reason, if it were not founded on the very nature of things, which is the ultimate source of their identity.
It is impossible for a great number of causes to combine by chance, to produce an effect essentially one and perfect in its kind, as is the case, for instance, with the act of seeing, in which the various parts of the eye concur. If this act were the effect of chance, something essentially one would be the result of an accidental combination (ens per se ab ente per accidens produceretur), the perfect would be produced by the imperfect, order would result from the absence of order, and the greater would proceed from the less. Such being the case, the unity and perfection of the effect would be without a raison d’être, which is absurd.…Chance, therefore, leaves everything to be explained. To wish to explain all things by it, to say that it is the cause of order in the universe, is tantamount to saying that there are effects without causes, that the greater comes from the less, the higher from the lower; that the accidental is prior to the essential, that the essential is but a name—a denial of the principle of identity—that, in consequence, the real is not intelligible.
b) Things do not act merely out of necessity
The second objection goes to the opposite extreme and says that things operate by necessity, which explains their activity without any recourse to some positive ordination towards their actions to account for them. There is no need to posit a final cause for natural actions, they have only efficient causes. Thus birds do not have wings in order to fly, rather they fly because they have wings.
What is denied by this objection is the validity of the principle of finality, that is, that every agent acts not just because of an efficient cause but for a final cause. There is a reason why things act as they do, it is not just by “necessity” (which amounts to saying that they act the way they do “because they do,” which is no reason at all). This is obvious because we see that, in fact, they act always (or nearly always) in a particular way and in a particular way that produces a result that is their good. There must be some cause for this, the agent must be ordained towards this action as to an end.
Again, Garrigou-Lagrange explains this very clearly by explaining what an end is.
The end is a determined perfection which it is fitting for the agent to have as a good of its own and for the sake of which the agent acts. Now, every agent, according to the law governing its nature, produces a determined effect, which belongs to it as its perfection, and it cannot produce this effect, unless it tends towards this effect in preference to any other, and unless it is ordained towards the same.
Thus without reasoning we discover that the eye is made for seeing, the ear for hearing, the wings for flying, etc.…The self-evident principle of finality can be defended by showing that it refers back to the principle of sufficient reason, so that to deny the former would lead to a denial of the latter. St. Thomas briefly points this out when he says that “Every agent acts for an end: otherwise one thing rather than another would not follow from the action of the agent.” (I, q. 44, a. 4) If every agent produces, not any sort of effect indifferently, but a determinate and suitable effect, and this without tending towards this effect, without being ordained towards this effect rather than towards another; if the acorn produces the oak and not the ash, without its having a definite tendency for the one rather than for the other; if the eye sees instead of hearing, without being meant for seeing rather than hearing–it follows that the non-accidental determination and appropriateness of the effect are without a raison d’être, that determination comes from indetermination, that order arises from the lack of order, that the perfect originates from the imperfect, the greater from the less–all of which statements are absurd.
It is clear, then, that in the world we see that things without intelligence act for an end. The argument concludes from this that there must be an intelligence then that directs them to this end, since it is only an intelligence that can order means to an end. Once more Garrigou-Lagrange explains:
Does this relation of means to end, this orderly arrangement of things, demand an intelligent cause? (…Yes, it does, for) only an intelligent being can perceive this relation, because a being endowed with intelligence, instead of merely associating or juxtaposing images, perceives the reasons why things are, and the means is related to the end as such precisely because it has its raison d’être in the end.…We say that this order is the result of intelligent design, not only because chance, blind necessity, instinct, or blind freedom explain nothing, but also because order presupposes that the means find their raison d’être in the end, and because it is of the very essence of intelligence to perceive the raison d’être, which is its formal object.
Refutation of two objections to the existence of God
In two brief objections St. Thomas marvelously sums up all the objections raised against the existence of God. The first is the classical argument from the existence of evil. If God exists, He is infinitely good and so He must exclude all evil in the world. Now evil exists in the world, therefore God does not exist.
St. Thomas neatly sidesteps this attack and turns it around against the adversary by simply citing an equally classic text of St. Augustine:
As Augustine says “Since God is supremely good, He would never allow any evil to exist in His works, unless He were so omnipotent and so good that He can bring good even out of evil.” Therefore it belongs to the infinite goodness of God that He should allow evils and bring good out of them.
John of St. Thomas, following Cajetan, gives a more developed response to the objection, distinguishing between something excluding its opposite formally and excluding it effectively. One form necessarily completely excludes its opposite from something when it informs it: God, however, does not inform His creatures but just Himself, so His infinite goodness necessarily excludes evil formally from Himself but not from His creatures. As for effective exclusion, a cause necessarily excludes its opposite from its effect if it is what is called an univocal cause, that is, when the cause and its effect are equal, as when a father generates a son. God, however, is not an univocal cause of His creation but an analogical cause, that is, His effect is not equal to Himself but only participates in His perfection to a certain limited degree and is therefore susceptible of suffering defects.
Thus God does not absolutely exclude evil from creatures but only in so far as is required by the very order of the whole, in which there must be some things which are indefectible, and others which are deficient, and where all things are not equally good: as is the case in the human body where all members are not equal.
The second objection maintains that God is not necessary since Nature sufficiently explains natural effects while human reason and will accounts for those which come about by free choice. St. Thomas responds by recalling what was shown in the proofs. Nature itself works for an end and thus requires a cause to direct it to that end. Human reason and will, also, cannot be the ultimate reason for what is done voluntarily because they are changeable and defectible and so require a cause which is immovable and necessary.
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