Summa Contra Gentiles
from Book I: Of God
Translated with an Introduction
by Anton C. PEGIS
University of Notre Dame Press,
Notre Dame, 1975
Part I, Question 2: The Existence of God
Basic Writings of St. Thomas Aquinas. Vol. I
Edited and Annotated, with an Introduction
by Anton C. PEGIS
Random House, New York 1945
AMERICAN UNIVERSITY OF BEIRUT
THOMAS AQUINAS (1225 74)
Summa contra Gentiles
Book I: Of God. Chapters ii – ix
Ch. ii. THE AUTHOR'S INTENTION IN THE PRESENT WORK
AMONG all human pursuits, the pursuit of wisdom is more perfect, more noble, more useful, and more full of joy.
It is more perfect because, in so far as a man gives himself to the pursuit of wisdom, so far does he even now have some share in true beatitude. And so a wise man has said: "Blessed is the man that shall continue in wisdom" (Ecclus. 14:22).
It is more noble because through this pursuit man especially approaches to a likeness to God Who "made all things in wisdom" (Ps. 103:24). And since likeness is the cause of love, the pursuit of wisdom especially joins man to God in friendship. That is why it is said of wisdom that "she is an infinite treasure to men, which they that use become the friends of God" (Wis. 7:14).
It is more useful because through wisdom we arrive at the kingdom of immortality. For "the desire of wisdom bringeth to the everlasting kingdom" (Wis. 6:21).
It is more full of joy because "her conversation hath no bitterness, nor her company any tediousness, but joy and gladness" (Wis. 7:16).
And so, in the name of the divine Mercy, I have the confidence to embark upon the work of a wise man, even though this may surpass my powers, and I have set myself the task of making known, as far as my limited powers will allow, the truth that the Catholic faith professes, and of setting aside the errors that are opposed to it. To use the words of Hilary: "I am aware that I owe this to God as the chief duty of my life, that my every word and sense may speak of him."1
Ch. iii. ON THE WAY IN WHICH DIVINE TRUTH IS TO BE MADE KNOWN
The way of making truth known is not always the same, and, as the Philosopher has very well said, "it belongs to an educated man to seek such certitude in each thing as the nature of that thing allows."2 The remark is also introduced by Boethius.3 But, since such is the case, we must first show what way is open to us in order that we may make known the truth which is our object.
There is a twofold mode of truth in what we profess about God. Some truths about God exceed all the ability of the human reason. Such is the truth that God is triune. But there are some truths which the natural reason also is able to reach. Such are that God exists, that He is one, and the like. In fact, such truths about God have been proved demonstratively by the philosophers, guided by the light of the natural reason.
That there are certain truths about God that totally surpass man's ability appears with the greatest evidence. Since, indeed, the principle of all knowledge that the reason perceives about some thing is the understanding of the very substance of that being (for according to Aristotle 'what a thing is' is the principle of demonstration),4 it is necessary that the way in which we understand the substance of a thing determines the way in which we know what belongs to it. Hence, if the human intellect comprehends the substance of some thing ― for example, that of a stone or of a triangle ― no intelligible characteristic belonging to that thing surpasses the grasp of the human reason. But this does not happen to us in the case of God. For the human intellect is not able to reach a comprehension of the divine substance through its natural power. For, according to its manner of knowing in the present life, the intellect depends on the sense for the origin of knowledge; and so those things that do not fall under the senses cannot be grasped by the human intellect except in so far as the knowledge of them is gathered from sensible things. Now, sensible things cannot lead the human intellect to the point of seeing in them the nature of the divine substance, for sensible things are effects that fall short of the power of their cause. Yet, beginning with sensible things, our intellect is led to the point of knowing about God that He exists, and other such characteristics that must be attributed to the First Principle. There are, consequently, some intelligible truths about God that are open to the human reason, but there are others that absolutely surpass its power.
We may easily see the same point from the gradation of intellects. Consider the case of two persons of whom one has a more penetrating grasp of a thing by his intellect than does the other. He who has the superior intellect understands many things that the other cannot grasp at all. Such is the case with a very simple person who cannot at all grasp the subtle speculations of philosophy. But the intellect of an angel surpasses the human intellect much more than the intellect of the greatest philosopher surpasses the intellect of the most uncultivated simple person; for the distance between the best philosopher and a simple person is contained within the limits of the human species, which the angelic intellect surpasses. For the angel knows God on the basis of a more noble effect than does man, and this by as much as the substance of an angel, through which the angel in his natural knowledge is led to the knowledge of God, is nobler than sensible things and even than the soul itself, through which the human intellect mounts to the knowledge of God. The divine intellect surpasses the angelic intellect much more than the angelic surpasses the human. For the divine intellect is in its capacity equal to its substance, and therefore it understands fully what it is, including all its intelligible attributes. But by his natural knowledge the angel does not know what God is, since the substance itself of the angel, through which he is led to the knowledge of God, is an effect that is not equal to the power of its cause. Hence, the angel is not able, by means of his natural knowledge, to grasp all the things that God understands in Himself, nor is the human reason sufficient to grasp all the things that the angel understands through his own natural power. Just as, therefore, it would be the height of folly for a simple person to assert that what a philosopher proposes is false on the ground that he himself cannot understand it, so (and even more so) it is the acme5 of stupidity for a man to suspect as false what is divinely revealed through the ministry of the angels simply because it cannot be investigated by reason.
The same thing, moreover, appears quite clearly from the defect that we experience every day in our knowledge of things. We do not know a great many of the properties of sensible things, and in most cases we are not able to discover fully the natures of those properties that we apprehend by the senses. Much more is it the case, therefore, that the human reason is not equal to the task of investigating all the intelligible characteristics of that most excellent substance.
The remark of Aristotle likewise agrees with this conclusion. He says that "our intellect is related to the prime beings, which are most evident in their nature, as the eye of an owl is related to the sun."6
Sacred Scripture also gives testimony to this truth. We read in Job: "Peradventure thou wilt comprehend the steps of God, and wilt find out the Almighty perfectly?" (11:7). And again: "Behold, God is great, exceeding our knowledge" (Job 36:26). And St. Paul: "We know in part" (I Cor. 13:9).
We should not, therefore, immediately reject as false, following the opinion of the Manicheans and many unbelievers, everything that is said about God even though it cannot be investigated by reason.
Ch. iv. THAT THE TRUTH ABOUT GOD TO WHICH THE NATURAL REASON REACHES
IS FITTINGLY PROPOSED TO MEN FOR BELIEF
Since, therefore, there exists a twofold truth concerning the divine being, one to which the inquiry of the reason can reach, the other which surpasses the whole ability of the human reason, it is fitting that both of these truths be proposed to man divinely for belief. This point must first be shown concerning the truth that is open to the inquiry of the reason; otherwise it might perhaps seem to someone that, since such a truth can be known by the reason, it was uselessly given to men through a supernatural inspiration as an object of belief.
Yet, if this truth were left solely as a matter of inquiry for the human reason, three awkward consequences would follow.
The first is that few men would possess the knowledge of God. For there are three reasons why most men are cut off from the fruit of diligent inquiry which is the discovery of truth. Some do not have the physical disposition for such work. As a result, there are many who are naturally not fitted to pursue knowledge; and so, however much they tried, they would be unable to reach the highest level of human knowledge which consists in knowing God. Others are cut off from pursuing this truth by the necessities imposed upon them by their daily lives. For some men must devote themselves to taking care of temporal matters. Such men would not be able to give so much time to the leisure of contemplative inquiry as to reach the highest peak at which human investigation can arrive, namely, the knowledge of God. Finally, there are some who are cut off by indolence. In order to know the things that the reason can investigate concerning God, a knowledge of many things must already be possessed. For almost all of philosophy is directed towards the knowledge of God, and that is why metaphysics, which deals with divine things, is the last part of philosophy to be learned. This means that we are able to arrive at the inquiry concerning the aforementioned truth only on the basis of a great deal of labor spent in study. Now, those who wish to undergo such a labor for the mere love of knowledge are few, even though God has inserted into the minds of men a natural appetite for knowledge.
The second awkward effect is that those who would come to discover the above mentioned truth would barely reach it after a great deal of time. The reasons are several. There is the profundity of this truth, which the human intellect is made capable of grasping by natural inquiry only after a long training. Then, there are many things that must be presupposed, as we have said. There is also the fact that, in youth, when the soul is swayed by the various movements of the passions, it is not in a suitable state for the knowledge of such lofty truth. On the contrary, "one becomes wise and knowing in repose," as it is said in the Physics.7 The result is this. If the only way open to us for the knowledge of God were solely that of the reason, the human race would remain in the blackest shadows of ignorance. For then the knowledge of God, which especially renders men perfect and good, would come to be possessed only by a few, and these few would require a great deal of time in order to reach it.
The third awkward effect is this. The investigation of the human reason for the most part has falsity present within it, and this is due partly to the weakness of our intellect in judgment, and partly to the admixture of images. The result is that many, remaining ignorant of the power of demonstration, would hold in doubt those things that have been most truly demonstrated. This would be particularly the case since they see that, among those who are reputed to be wise men, each one teaches his own brand of doctrine. Furthermore, with the many truths that are demonstrated, there sometimes is mingled something that is false, which is not demonstrated but rather asserted on the basis of some probable or sophistical argument, which yet has the credit of being a demonstration. That is why it was necessary that the unshakeable certitude and pure truth concerning divine things should be presented to men by way of faith.
Beneficially, therefore, did the divine Mercy provide that it should instruct us to hold by faith even those truths that the human reason is able to investigate. In this way, all men would easily be able to have a share in the knowledge of God, and this without uncertainty and error. (...)
Ch. v. THAT THE TRUTHS THE HUMAN REASON IS NOT ABLE TO INVESTIGATE
ARE FITTINGLY PROPOSED TO MEN FOR BELIEF
Now, perhaps some will think that men should not be asked to believe what the reason is not adequate to investigate, since the divine Wisdom provides in the case of each thing according to the mode of its nature. We must therefore prove that it is necessary for man to receive from God as objects of belief even those truths that are above the human reason.
No one tends with desire and zeal towards something that is not already known to him. But, as we shall examine later on in this work, men are ordained by the divine Providence towards a higher good than human fragility can experience in the present life. That is why it was necessary for the human mind to be called to something higher than the human reason here and now can reach, so that it would thus learn to desire something and with zeal tend towards something that surpasses the whole state of the present life. This belongs especially to the Christian religion, which in a unique way promises spiritual and eternal goods. And so there are many things proposed to men in it that transcend human sense. The Old Law, on the other hand, whose promises were of a temporal character, contained very few proposals that transcended the inquiry of the human reason. Following this same direction, the philosophers themselves, in order that they might lead men from the pleasure of sensible things to virtue, were concerned to show that there were in existence other goods of a higher nature than these things of sense, and that those who gave themselves to the active or contemplative virtues would find much sweeter enjoyment in the taste of these higher goods.
It is also necessary that such truth be proposed to men for belief so that they may have a truer knowledge of God. For then only do we know God truly when we believe Him to be above everything that it is possible for man to think about Him; for, as we have shown,8 the divine substance surpasses the natural knowledge of which man is capable. Hence, by the fact that some things about God are proposed to man that surpass his reason, there is strengthened in man the view that God is something above what he can think.
Another benefit that comes from the revelation to men of truths that exceed the reason is the curbing of presumption, which is the mother of error. For there are some who have such a presumptuous opinion of their own ability that they deem themselves able to measure the nature of everything; I mean to say that, in their estimation, everything is true that seems to them so, and everything is false that does not. So that the human mind, therefore, might be freed from this presumption and come to a humble inquiry after truth, it was necessary that some things should be proposed to man by God that would completely surpass his intellect.
A still further benefit may also be seen in what Aristotle says in the Ethics.9 There was a certain Simonides who exhorted people to put aside the knowledge of divine things and to apply their talents to human occupations. He said that "he who is a man should know human things, and he who is mortal, things that are mortal." Against Simonides Aristotle says that "man should draw himself towards what is immortal and divine as much as he can." And so he says in the De animalibus10 that, although what we know of the higher substances is very little, yet that little is loved and desired more than all the knowledge that we have about less noble substances. He also says in the De caelo et mundo11 that when questions about the heavenly bodies can be given even a modest and merely plausible solution, he who hears this experiences intense joy. From all these considerations it is clear that even the most imperfect knowledge about the most noble realities brings the greatest perfection to the soul. Therefore, although the human reason cannot grasp fully the truths that are above it, yet, if it somehow holds these truths at least by faith, it acquires great perfection for itself.
Therefore it is written: "For many things are shown to thee above the understanding of men" (Ecclus. 3:25). Again: "So the things that are of God no man knoweth but the Spirit of God. But to us God hath revealed them by His Spirit" (I Cor. 2:10 11).
Ch. vi. THAT TO GIVE ASSENT TO THE TRUTHS OF FAITH IS NOT FOOLISHNESS
EVEN THOUGH THEY ARE ABOVE REASON
Those who place their faith in this truth, however, "for which the human reason offers no experimental evidence," do not believe foolishly, as though "following artificial fables" (11 Peter 1:16). For these "secrets of divine Wisdom" (Job 11:6) the divine Wisdom itself, which knows all things to the full, has deigned to reveal to men. It reveals its own presence, as well as the truth of its teaching and inspiration, by fitting arguments; and in order to confirm those truths that exceed natural knowledge, it gives visible manifestation to works that surpass the ability of all nature. Thus, there are the wonderful cures of illnesses, there is the raising of the dead, and the wonderful immutation in the heavenly bodies; and what is more wonderful, there is the inspiration given to human minds, so that simple and untutored persons, filled with the gift of the Holy Spirit, come to possess instantaneously the highest wisdom and the readiest eloquence. When these arguments were examined, through the efficacy of the abovementioned proof, and not the violent assault of arms or the promise of pleasures, and (what is most wonderful of all) in the midst of the tyranny of the persecutors, an innumerable throng of people, both simple and most learned, flocked to the Christian faith. In this faith there are truths preached that surpass every human intellect; the pleasures of the flesh are curbed; it is taught that the things of the world should be spurned. Now, for the minds of mortal men to assent to these things is the greatest of miracles, just as it is a manifest work of divine inspiration that, spurning visible things, men should seek only what is invisible. Now, that this has happened neither without preparation nor by chance, but as a result of the disposition of God, is clear from the fact that through many pronouncements of the ancient prophets God had foretold that He would do this. The books of these prophets are held in veneration among us Christians, since they give witness to our faith. (...)
Ch. vii. THAT THE TRUTH OF REASON IS NOT OPPOSED TO THE TRUTH OF
THE CHRISTIAN FAITH
Now, although the truth of the Christian faith which we have discussed surpasses the capacity of the reason, nevertheless that truth that the human reason is naturally endowed to know cannot be opposed to the truth of the Christian faith. For that with which the human reason is naturally endowed is clearly most true; so much so, that it is impossible for us to think of such truths as false. Nor is it permissible to believe as false that which we hold by faith, since this is confirmed in a way that is so clearly divine. Since, therefore, only the false is opposed to the true, as is clearly evident from an examination of their definitions, it is impossible that the truth of faith should be opposed to those principles that the human reason knows naturally.
Furthermore, that which is introduced into the soul of the student by the teacher is contained in the knowledge of the teacher ― unless his teaching is fictitious, which it is improper to say of God. Now, the knowledge of the principles that are known to us naturally has been implanted in us by God, for God is the Author of our nature. These principles, therefore, are also contained by the divine Wisdom. Hence, whatever is opposed to them is opposed to the divine Wisdom, and, therefore, cannot come from God. That which we hold by faith as divinely revealed, therefore, cannot be contrary to our natural knowledge.
Again: in the presence of contrary arguments our intellect is chained, so that it cannot proceed to the knowledge of the truth. If, therefore, contrary knowledges were implanted in us by God, our intellect would be hindered from knowing truth by this very fact. Now, such an effect cannot come from God.
And again: what is natural cannot change as long as nature does not. Now, it is impossible that contrary opinions should exist in the same knowing subject at the same time. No opinion or belief, therefore, is implanted in man by God which is contrary to man's natural knowledge.
Therefore, the Apostle says: "The word is nigh thee, even in thy mouth and in thy heart. This is the word of faith, which we preach" (Rom. 10:8). But because it overcomes reason, there are some who think that it is opposed to it: which is impossible.
The authority of St. Augustine also agrees with this. He writes as follows: "That which truth will reveal cannot in any way be opposed to the sacred books of the Old and the New Testament."12
From this we evidently gather the following conclusion: Whatever arguments are brought forward against the doctrines of faith are conclusions incorrectly derived from the first and self evident principles imbedded in nature. Such conclusions do not have the force of demonstration; they are arguments that are either probable or sophistical. And so, there exists the possibility to answer them,
Ch. viii. HOW THE HUMAN REASON IS RELATED TO THE TRUTH OF FAITH
There is also a further consideration. Sensible things, from which the human reason takes the origin of its knowledge, retain within themselves some sort of trace of a likeness to God. This is so imperfect, however, that it is absolutely inadequate to manifest the substance of God. For effects bear within themselves, in their own way, the likeness of their causes, since an agent produces its like; yet an effect does not always reach to the full likeness of its cause. Now, the human reason is related to the knowledge of the truth of faith (a truth which can be most evident only to those who see the divine substance) in such a way that it can gather certain likenesses of it, which are yet not sufficient so that the truth of faith may be comprehended as being understood demonstratively or through itself. Yet it is useful for the human reason to exercise itself in such arguments, however weak they may be, provided only that there be present no presumption to comprehend or to demonstrate. For to be able to see something of the loftiest realities, however thin and weak the sight may be, is, as our previous remarks indicate, a cause of the greatest joy.
The testimony of Hilary agrees with this. Speaking of this same truth, he writes as follows in his De Trinitate:13 "Enter these truths by believing, press forward, persevere. And though I may know that you will not arrive at an end, yet I will congratulate you in your progress. For, though he who pursues the infinite with reverence will never finally reach the end, yet he will always progress by pressing onward. But do not intrude yourself into the divine secret, do not, presuming to comprehend the sum total of intelligence, plunge yourself into the mystery of the unending nativity: rather, understand that these things are incomprehensible."
Ch. ix. THE ORDER AND MANNER OF PROCEDURE IN THE PRESENT WORK
It is clearly apparent, from what has been said, that the intention of the wise man ought to be directed toward the twofold truth of divine things, and toward the destruction of the errors that are contrary to this truth. One kind of divine truth the investigation of the reason is competent to reach, whereas the other surpasses every effort of the reason. I am speaking of a "twofold truth of divine things," not on the part of God Himself, Who is truth one and simple, but from the point of view of our knowledge, which is variously related to the knowledge of divine things.
Now, to make the first kind of divine truth known, we must proceed through demonstrative arguments, by which our adversary may become convinced. However, since such arguments are not available for the second kind of divine truth, our intention should not be to convince our adversary by arguments: it should be to answer his arguments against the truth; for, as we have shown,14 the natural reason cannot be contrary to the truth of faith. The sole way to overcome an adversary of divine truth is from the authority of Scripture ― an authority divinely confirmed by miracles. For that which is above the human reason we believe only because God has revealed it. Nevertheless, there are certain likely arguments that should be brought forth in order to make divine truth known. This should be done for the training and consolation of the faithful, and not with any idea of refuting those who are adversaries. For the very inadequacy of the arguments would rather strengthen them in their error, since they would imagine that our acceptance of the truth of faith was based on such weak arguments.
This, then, is the manner of procedure we intend to follow. We shall first seek to make known that truth which faith professes and reason investigates. This we shall do by bringing forward both demonstrative and probable arguments, some of which were drawn from the books of the philosophers and of the saints, through which truth is strengthened and its adversary overcome. Then, in order to follow a development from the more manifest to the less manifest, we shall proceed to make known that truth which surpasses reason, answering the objections of its adversaries and setting forth the truth of faith by probable arguments and by authorities, to the best of our ability.
We are aiming, then, to set out following the way of the reason and to inquire into what the human reason can investigate about God. In this aim the first consideration that confronts us is of that which belongs to God in Himself. The second consideration concerns the coming forth of creatures from God. The third concerns the ordering of creatures to God as to their end.
Now, among the inquiries that we must undertake concerning God in Himself, we must set down in the beginning that whereby His Existence is demonstrated, as the necessary foundation of the whole work. For, if we do not demonstrate that God exists, all consideration of divine things is necessarily suppressed.
Question II: The Existence of God
(In Three Articles)
BECAUSE the chief aim of sacred doctrine is to teach the knowledge of God not only as He is in Himself, but also as He is the beginning of things and their last end, and especially of rational creatures, as is clear from what has been already said, therefore, in our endeavor to expound this science, we shall treat: (1) of God; (2) of the rational creature's movement towards God; (3) of Christ Who as man is our way to God.
In treating of God there will be a threefold division:
For we shall consider (1) whatever concerns the divine essence. (2) Whatever concerns the distinctions of Persons. (3) Whatever concerns the procession of creatures from Him.
Concerning the divine essence, we must consider:―
(1) Whether God exists? (2) The manner of His existence, or, rather, what is not the manner of His existence. (3) Whatever concerns His operations ― namely, His knowledge, will, power.
Concerning the first, there are three points of inquiry:
Whether the proposition God exists is self evident? (2) Whether it is demonstrable? (3) Whether God exists?
WHETHER THE EXISTENCE OF GOD IS SELF EVIDENT?
We proceed thus to the First Article:―
Objection 1. It seems that the existence of God is self evident. For those things are said to be self evident to us the knowledge of which exists naturally in us, as we can see in regard to first principles. But as Damascene says, the knowledge of God is naturally implanted in all.15 Therefore the existence of God is self evident.
Obj. 2. Further, those things are said to be self evident which are known as soon as the terms are known, which the Philosopher says is true of the first principles of demonstration.16 Thus, when the nature of a whole and of a part is known, it is at once recognized that every whole is greater than its part. But as soon as the signification of the name God is understood, it is at once seen that God exists. For by this name is signified that thing than which nothing greater can be conceived. But that which exists actually and mentally is greater than that which exists only mentally. Therefore, since as soon as the name God is understood it exists mentally, it also follows that it exists actually. Therefore the proposition God exists is self evident.
Obj. 3. Further, the existence of truth is self evident. For whoever denies the existence of truth grants that truth does not exist: and, if truth does not exist, then the proposition Truth does not exist is true: and if there is anything true, there must be truth. But God is truth itself: I am the way, the truth, and the life (Jo. xiv.6). Therefore God exists is self evident.
On the contrary, No one can mentally admit the opposite of what is self-evident, as the Philosopher states concerning the first principles of demonstration.17 But the opposite of the proposition God is can be mentally admitted: The fool said in his heart, There is no God (Ps. Iii.1). Therefore, that God exists is not self evident.
I answer that, A thing can be self evident in either of two ways: on the one hand, self evident in itself, though not to us; on the other, self evident in itself, and to us. A proposition is self evident because the predicate is included in the essence of the subject: e.g., Man is an animal, for animal is contained in the essence of man. If, therefore, the essence of the predicate and subject be known to all, the proposition will be self evident to all; as is clear with regard to the first principles of demonstration, the terms of which are certain common notions that no one is ignorant of, such as being and non being, whole and part, and the like. If, however, there are some to whom the essence of the predicate and subject is unknown, the proposition will be self evident in itself, but not to those who do not know the meaning of the predicate and subject of the proposition. Therefore, it happens, as Boethius says,18 that there are some notions of the mind which are common and self evident only to the learned, as that incorporeal substances are not in space. Therefore I say that this proposition, God exists, of itself is self evident, for the predicate is the same as the subject, because God is His own existence as will be hereafter shown. Now because we do not know the essence of God, the proposition is not self evident to us, but needs to be demonstrated by things that are more known to us, though less known in their nature ― namely, by His effects.
Reply Obj. 1. To know that God exists in a general and confused way is implanted in us by nature, inasmuch as God is man's beatitude. For man naturally desires happiness, and what is naturally desired by man is naturally known by him. This, however, is not to know absolutely that God exists; just as to know that someone is approaching is not the same as to know that Peter is approaching, even though it is Peter who is approaching; for there are many who imagine that man's perfect good, which is happiness, consists in riches, and others in pleasures, and others in something else.
Reply Obj. 2. Perhaps not everyone who hears this name God understands it to signify something than which nothing greater can be thought, seeing that some have believed God to be a body. Yet, granted that everyone understands that by this name God is signified something than which nothing greater can be thought, nevertheless, it does not therefore follow that he understands that what the name signifies exists actually, but only that it exists mentally. Nor can it be argued that it actually exists, unless it be admitted that there actually exists something than which nothing greater can be thought; and this precisely is not admitted by those who hold that God does not exist.
Reply Obj. 3. The existence of truth in general is self evident, but the existence of a Primal Truth is not self evident to us.
WHETHER IT CAN BE DEMONSTRATED THAT GOD EXISTS?
We proceed thus to the Second Article: ―
Objection 1. It seems that the existence of God cannot be demonstrated. For it is an article of faith that God exists. But what is of faith cannot be demonstrated, because a demonstration produces scientific knowledge, whereas faith is of the unseen, as is clear from the Apostle (Heb. xi. 1). Therefore it cannot be demonstrated that God exists.
Obj. 2. Further, essence is the middle term of demonstration. But we cannot know in what God's essence consists, but solely in what it does not consist, as Damascene says.19 Therefore we cannot demonstrate that God exists.
Obj. 3. Further, if the existence of God were demonstrated, this could only be from His effects. But His effects are not proportioned to Him, since He is infinite and His effects are finite, and between the finite and infinite there is no proportion. Therefore, since a cause cannot be demonstrated by an effect not proportioned to it, it seems that the existence of God cannot be demonstrated.
On the contrary, The Apostle says: The invisible things of Him are clearly seen, being understood by the things that are made (Rom. i.20). But this would not be unless the existence of God could be demonstrated through the things that are made; for the first thing we must know of anything is, whether it exists.
I answer that, Demonstration can be made in two ways: One is through the cause, and is called propter quid,20 and this is to argue from what is prior absolutely. The other is through the effect, and is called a demonstration quia;21 this is to argue from what is prior relatively only to us. When an effect is better known to us than its cause, from the effect we proceed to the knowledge of the cause. And from every effect the existence of its proper cause can be demonstrated, so long as its effects are better known to us; because, since every effect depends upon its cause, if the effect exists, the cause must pre-exist. Hence the existence of God, in so far as it is not self-evident to us, can be demonstrated from those of His effects which are known to us.
Reply Obj. 1. The existence of God and other like truths about God, which can be known by natural reason, are not articles of faith, but are preambles to the articles; for faith presupposes natural knowledge, even as grace presupposes nature and perfection the perfectible. Nevertheless, there is nothing to prevent a man, who cannot grasp a proof, from accepting, as a matter of faith, something which in itself is capable of being scientifically known and demonstrated.
Reply Obj. 2. When the existence of a cause is demonstrated from an effect, this effect takes the place of the definition of the cause in proving the cause's existence. This is especially the case in regard to God, because, in order to prove the existence of anything, it is necessary to accept as a middle term the meaning of the name, and not its essence, for the question of its essence follows on the question of its existence. Now the names given to God are derived from His effects, as will be later shown. Consequently, in demonstrating the existence of God from His effects, we may take for the middle term the meaning of the name God.
Reply Obj. 3. From effects not proportioned to the cause no perfect knowledge of that cause can be obtained. Yet from every effect the existence of the cause can be clearly demonstrated, and so we can demonstrate the existence of God from His effects; though from them we cannot know God perfectly as He is in His essence.
WHETHER GOD EXISTS?
We proceed thus to the Third Article:―
Objection 1. It seems that God does not exist; because if one of two contraries be infinite, the other would be altogether destroyed. But the name God means that He is infinite goodness. If, therefore, God existed, there would be no evil discoverable; but there is evil in the world. Therefore God does not exist.
Obj. 2. Further, it is superfluous to suppose that what can be accounted for by a few principles has been produced by many. But it seems that everything we see in the world can be accounted for by other principles, supposing God did not exist. For all natural things can be reduced to one principle, which is nature; and all voluntary things can be reduced to one principle, which is human reason, or will. Therefore there is no need to suppose God's existence.
On the contrary, It is said in the person of God: I am Who am (Exod. iii. 14).
I answer that, 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 moved is moved by another, for nothing can be moved except it is in potentiality to that towards which it is moved; 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 moved must be moved by another. If that by which it is moved be itself moved, then this also must needs be moved 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 moved by the first mover; as the staff moves only because it is moved by the hand. Therefore it is necessary to arrive at a first mover, moved by no other; and this everyone understands to be God.
The second way is from the nature of efficient cause. In the world of sensible things 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 one only. 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 be corrupted, and consequently, it is possible for them to be and not to be. But it is impossible for these always to exist, for that which can not be, at some time is not. Therefore, if everything can not be, then at one time there was nothing in existence. Now if this were true, even now there would be nothing in existence, because that which does not exist begins to exist only through 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 admit 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 most being, for those things that are greatest in truth are greatest in being, as it is written in Metaph. ii.22 Now the maximum in any genus is the cause of all in that genus, as fire, which is the maximum of heat, is the cause of all hot things, as is said in the same book.23 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 knowledge, 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 they achieve their end, not fortuitously, but designedly. Now whatever lacks knowledge cannot move towards an end, unless it be directed by some being endowed with knowledge and intelligence; as the arrow is directed by the archer. Therefore some intelligent being exists by whom all natural things are directed to their end; and this being we call God.
Reply Obj. 1. As Augustine says: Since God is the highest good, He would not allow any evil to exist in His works, unless His omnipotence and goodness were such as to bring good even out of evil.24 This is part of the infinite goodness of God, that He should allow evil to exist, and out of it produce good.
Reply Obj. 2. Since nature works for a determinate end under the direction of a higher agent, whatever is done by nature must be traced back to God as to its first cause. So likewise whatever is done voluntarily must be traced back to some higher cause other than human reason and will, since these can change and fail; for all things that are changeable and capable of defect must be traced back to an immovable and self necessary first principle, as has been shown.