Thomas' most significant work is his Summa theologiae or 'summary of Theology,' a gigantic work which attempts to present all of Christian theology as systematically as possible. Thomas worked on it from 1266 through 1273. Then, when he was nearly finished, he underwent an experience so intense that, as he himself explained, everything he had written seemed like straw. He completely stopped writing and died three months later. Thomas was canonized in 1323.
The Summa theologiae is written in a form common to treatises of that age. All of theology is divided into its major topics. These, in turn, are divided into subtopics described by Thomas as 'questions. " The first "question" in the Summa theologiae deals with The nature of Theology itself, the second with God's existence.
The 'questions" are in turn divided into what Thomas calls "articles," specific queries concerning the topic being explored in that particular "question." (Thus, confusingly enough, what Thomas calls "questions" are actually general topics, whereas what he calls "articles" are really what we would mean by the word "questions.") These "articles" form the basic unit of the Summa theologiae, and they proceed according to an invariable form. A specific query is made, then a section beginning with the word videtur ("it seems that") offers arguments for what will later turn out to be the wrong answer to that query. Next, a brief section beginning with the words sed contra ("but on the contrary") introduces a different answer. A section labeled responsio ("response") finally presents arguments for what Thomas considers the correct view. The question then closes with a refutation of the arguments presented in the videtur section.
The following selection consists of the prologue and first two questions of the Summa theologiae. Some articles of the first question are omitted, but those included are given in their entirety, so that the reader can see how the work (and Thomas' mind) is constructed.
The complete text of the Summa can be found here.
Prologue
Since a teacher of catholic truth should instruct not only the advanced but beginners as well - as St. Paul says, "Like babes in Christ I fed you milk and not meat" (I Cor. 3:1) - our intention in this work is to convey the content of the Christian religion in a way fit for the training of beginners. We have seen that novices in this study are greatly hindered by the various writings on the subject. They are hindered partly because of the multiplication of useless questions, articles and arguments in these writings; partly because the order in which essential material is delivered in these writings is determined, not by the nature of doctrine itself, but by the books on which the writings are commenting; and partly because frequent repetition has bred boredom and confusion in the minds of hearers.
Eager to avoid these and other pitfalls we shall now attempt to examine the content of sacred doctrine briefly and clearly, so far as the material allows, twisting in God's aid.
In order to contain our investigation within limits, we must first investigate sacred doctrine itself, asking what it is and how far it extends. Ten questions must be asked.
Whether it is necessary
Whether it is a science
Whether it is one or many
Whether it is speculative or practical
How it compares with other sciences
Whether it is wisdom
What is its subject
Whether it is argumentative
Whether it should use metaphorical or symbolic language
Whether the sacred scripture containing this doctrine is to be interpreted according to several senses.
Let us proceed to the first point. It seems that there is no necessity for any doctrine beyond the philosophical disciplines. Man should not strive after that which is beyond his reason. As Ecclesiastics says, "Do not be curious about what is above you" (Ecclus. 3:22). The things which can be investigated by reason are sufficiently covered in the philosophical disciplines, however. Thus it seems superfluous to have some doctrine beyond the philosophical disciplines.
Furthermore, any doctrine can deal only with that which is; for nothing can be known except that which is true, and that which is true is identical with that which is. Yet everything other than signification, through which the things signified by the words signify something else in turn, is called the spiritual sense. It is based on the literal sense and presupposes it.
But on the contrary Paul says, "All divinely-inspired scripture is useful for teaching, arguing, correcting and instructing in justice" (II Tim. 3:16). Divinely- inspired scripture does not pertain to philosophical disciplines, however, for they are discovered by human reason. Thus it is useful to have another, divinely- inspired doctrine besides the philosophical disciplines.
Response: It must be said that, besides the philosophical disciplines which are investigated by human reason, another doctrine based on revelation was necessary for human well-being. Such is true, in the first place, because man is ordered by God to a certain end which exceeds the grasp of reason. As Isaiah says, "Eye has not seen, God, without you, what you have prepared for those who love you" (lsa. 64:4). The end must be fore-known to man, however, since he must order his intentions and actions to that end. Thus it was necessary to human well-being that certain things exceeding human reason be made known to man through divine revelation.
Even in the case of those things which can be investigated by human reason, it was necessary for man to be instructed by divine revelation. The truth concerning God, if left to human reason alone, would have appeared only to a few, and only after a long search, and even then mixed with many errors; yet all of man's well-being, which is in God, depends on knowledge of this truth. Thus, in order that this well-being should become known to men more commonly and more securely, it was necessary that they be instructed by divine revelation.
Thus it was necessary that, besides the philosophical doctrines which can be investigated by reason, there be a sacred doctrine known through revelation.
To the first argument, therefore, it must be said that, although what is above human knowledge should not be investigated by reason, once revealed by God it should be accepted through faith. Thus it is added in the same chapter of Ecclesiasticus, "Many things above human understanding are shown to you" (Ecclus. 3:25). Sacred doctrine consists of these things.
To the second argument it must be said that there are diverse sciences because things can be known in various ways. For example, the astronomer and the natural philosopher both demonstrate the same conclusion, such as that the world is round; yet the astronomer does so through mathematics, while the natural philosopher does so in a way that takes matter into account. Thus there is no reason why those things treated by the philosophical disciplines through natural reason should not also be treated by another science insofar as they are known by the light of divine revelation. Thus the theology which pertains to sacred doctrine differs from that theology which is a part of philosophy.
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Let us proceed to the fifth point. It seems that sacred doctrine is not worthier than other sciences. Certitude contributes to the worth of a science; yet other sciences, the premises of which cannot be doubted, seem to be more certain than sacred doctrine, the principles of which (that is, the articles of faith) are open to doubt.
Furthermore, it is characteristic of a lower science to draw on a higher one, just as music draws on arithmetic. Sacred doctrine draws from the philosophical disciplines, for Jerome says that "the ancient teachers so filled their books with the doctrines and opinions of philosophers that you do not know which to marvel at first, their worldly erudition or their knowledge of the scriptures." Thus sacred doctrine is inferior to other sciences.
But on the contrary, other sciences are called the maidservants of this one. Proverbs says, "She has sent her servants to invite to the tower (Prov. 9:3).
Response: It must be said that, since this science is practical in one respect and speculative in another, it transcends all other sciences, both speculative and practical. Among the speculative sciences, one is said to be worthier than another either because of its certainty or because of the worth of its subject. This science exceeds all others on both counts. It does so in regard to certainty because other sciences gain their certainty through the light of natural reason, which can err, whereas this one gains its certainty through the light of divine wisdom, which cannot be deceived. It does so in regard to the dignity of its matter because this science deals principally with things which transcend reason, being above it, whereas other sciences consider only those things which are subject to reason.
Among the practical sciences, one is said to be worthier if it is ordered to a higher end. Thus the study of politics is worthier than that of warfare because the good of an army is ordered to the good of the city it serves. The end of this science insofar as it is practical is eternal bliss, to which all other practical sciences are ordered as the ultimate end. Thus it is evident that this science is worthier than all others in every way.
To the first argument, therefore, it must be said that there is nothing to prevent that which is more certain in itself from being less certain to us because of the weakness of our intellects, which, as Aristotle says, "are related to the most evident things as the eyes of a bat are to the sun." Thus the doubt some people experience regarding articles of the faith is not due to their uncertainty, but to the weakness of the human mind. Nevertheless, as Aristotle observes, the smallest inkling of the highest matters is more desirable than certain knowledge of the least important matters.
To the second argument it must be said that this science can borrow something from the philosophical disciplines, not because it needs to do so, but in order to clarify its content. For it accepts its principles, not from other sciences, but immediately from God through revelation. Thus it does not receive from other sciences as from superiors, but rather uses them as inferiors and servants, just as an architect uses workers or a statesman uses soldiers. Moreover, its use of other sciences is due, not to any defect or insufficiency within itself, but to a defect in our intellect, which are more easily led to the things above reason set forth in this science if they travel by way of those things known through natural reason, which is the source of other sciences.
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Thus we proceed to the eighth point. It seems that this doctrine cannot be defended through argument, for Ambrose says, "Away with argument where faith is sought!" Faith, however, is primarily sought in this doctrine, for as John says, "These things are written in order that you may believe" (Jn. 20:30). Thus sacred doctrine cannot be defended through argument.
But on the contrary, Paul says that a bishop should "embrace the faithful word according to sound doctrine, so that he will be able to exhort in sound doctrine and argue with those who deny it" (Titus 1:9).
Response: It must be said that other sciences do not argue to prove their premises, but rather argue from these premises to establish other times within the particular science. Thus this doctrine does not argue to prove its premises, which are the articles of faith, but proceeds from them to establish other things, just as the apostle Paul argues from the resurrection of Christ to prove a general resurrection (I Cor. 15:12).
It must be born in mind, then, that within the philosophical sciences the inferior sciences neither prove their principles nor dispute with those who deny them. They leave that task to a superior science. The supreme philosophical science, metaphysics, can dispute against someone who denies its premises only if the adversary will concede something. If he concedes nothing, then debate is impossible, although it may still be possible to show that the adversary's argument is invalid.
Thus sacred scripture, having no superior, can debate with one who denies its premises only if the adversary concedes some part of divine revelation. In this way we debate with heretics on the basis of sacred doctrine, using one article which they accept to support another which they deny. If the adversary believes nothing of what is revealed in sacred doctrine, then there is no way left to prove the articles of faith through reason. It is still possible to refute arguments advanced against the faith, however. Since the faith rests upon infallible truth and it is impossible to prove what is contrary to truth, it is clear that arguments against the faith are not really proofs and can be refuted.
To the first argument, therefore, it must be said that the arguments of human reason cannot prove the faith, but one can argue from articles of faith to other conclusions, as was said above.
To the second, it must be said that argument from authority is very appropriate to this doctrine, since its premises are derived from revelation. Thus one must believe in the authority of those to whom the revelation was given. Nor does this fact derogate from the worth of this doctrine, for an argument from authority may be the weakest kind when it is based on human revelation, but it is the strongest kind when based on divine revelation.
Nevertheless, sacred doctrine also uses human reason. It does so not to prove the faith - for that would detract from the merit of faith - but to clarify some of its implications. Therefore, since grace protects nature rather than erasing it, natural reason should serve faith just as the natural inclination of the will obeys love. The apostle Paul speaks of "bringing every understanding into captivity in the service of Christ" (II Cor. 10:5). Thus sacred doctrine appeals to the authority of philosophers in those areas where they were able to arrive at the truth through natural reason, just as Paul employs a passage from Aratus, saying, "As some of your poets have said, we are the offspring of God" (Acts 17:28).
Nevertheless, sacred doctrine employs such authorities only insofar as they can provide extraneous arguments, the proofs of which are probable rather than certain. It appeals to the authority of canonical scripture as an authority proper to itself, that of the teachers of the church, but here again the arguments are merely probable. For our faith rests on the revelation made to the apostles and prophets who wrote the canonical books, and not on any revelation (if such there was) made to teachers. Thus Augustine says in his letter to Jerome, "Only to those books of the scripture called 'canonical' have I learned to pay such honor that I believe no author to have erred in writing them. Other writers I read in such a way that, whatever holiness and learning they display, I do not consider what they say to be true simply because they say it."
Thus we proceed to the ninth point. It seems that holy scripture should not use metaphors. That which is proper to a lower type of learning does not seem fitting for this science, which, as has been said, holds the highest place. It is proper to poetry, the lowest type of learning, to proceed through various similitudes and representations, however. Thus the use of such similitudes is not fitting for this science.
Furthermore, it seems that the purpose of this doctrine is to make the truth appear plainly, and there is a reward promised to those who do so. Ecclesiasticus says, "Those who explain me shall have eternal life" (Ecclus. 24:31). The truth is hidden through similitudes, however. Thus it is unfitting for this doctrine to convey divine matters through similitudes taken from the corporeal world.
Furthermore, the more sublime creatures are, the more similar they are to God. If, then, some properties of created beings are used in speaking of God, then they should be taken from higher rather than lower creatures. This is, however, frequently the case in scripture.
But on the contrary, in Hosea God says, "I have multiplied visions in them and I have used similitudes by the ministry of the prophets" (Hos. 12:10). To communicate something by similitude is to speak metaphorically. Thus sacred doctrine employs metaphors.
Response: It must be said that the communication of divine and spiritual things through corporeal similitudes is quite fitting for holy scripture. God provides for all things according to their natures. It is natural for man to attain knowledge through the use of sensible things, for all of our knowledge begins with sense experience. Thus in sacred scripture spiritual matters are quite properly conveyed to us through metaphors taken from the corporeal world. That is what Dionysius means when he says, "The divine rays cannot illuminate us unless they are wrapped in many sacred veils.
The presentation of spiritual matters through corporeal similitudes is also fitting because holy scripture is addressed to all of us in common. As Paul says, "I am a debtor to the wise and to the foolish" (Rom. 1:14). Scripture discusses spiritual matters in the form of physical likenesses so that they can be understood by the uneducated, who are incapable of understanding them in themselves.
To the first argument, therefore, it must be said that poetry uses metaphors for the sake of representation, for representation is naturally delightful to man. Sacred doctrine, however, uses metaphors because they are necessary and useful, as has been said.
To the second it must be said that the ray of divine revelation is not destroyed by the sensible figures veiling it, but, as Dionysius says, it remains in its truth in order that the minds receiving the revelation should not be permitted to stay on the level of the similitudes but should be raised to an understanding of the ideas behind them, and so that others should be instructed by those to whom the revelation is made. To this end the things conveyed through metaphor in one part of scripture are more directly explained in other parts.
Moreover, veiling the message in metaphor has certain advantages. It is good training for scholars and guards the faith against ridicule by infidels, of whom Christ speaks when he says, "Do not throw that which is holy to the dogs" (Mtt. 7:6).
In reply to the third, it must be said that, as Dionysius teaches, divine things are more fittingly conveyed in scripture by the images of vile bodies than by images of noble bodies. There are three reasons why this is so. First, it guards us against error, since there can be no doubt that such images are not literally true. If divine things were described in terms of noble bodies, such a mistake might be made, particularly by those who can things of nothing nobler than a body. Second, because this practice is more appropriate to the knowledge of God attained in this life, when we see what God is not more clearly than what he is. Thus similitudes taken from things furthest removed from God give us a truer picture of him in the sense that they convey how far above our word or thought he really is. Third, because in this way divine things are more effectively hidden from the unworthy.
Thus we proceed to the tenth point. It seems that the same passage of holy scripture cannot have several senses, namely the historical or literal, the allegorical, the tropological or moral, and the anagogical. Multiple senses in scripture prepare the way for confusion and deception. They also compromise coherent reasoning. From several propositions there results, not an argument, but a collection of fallacies. Sacred scripture, however, should display the truth without any fallacy whatsoever. Thus there should not be several senses in the same passage.
Furthermore, Augustine says, "The scripture which is called 'The Old Testament' has a fourfold meaning, namely history, etiology, analogy and allegory." These four seem inconsistent with the aforementioned. Thus it does not seem fitting that the same passage of sacred scripture should be exposited according to the four aforementioned senses.
Furthermore, there is also a parabolic sense, which does not seem to be included among these four senses.
But on the contrary Gregory says, "Sacred scripture transcends all other sciences in the manner of its expression, because in one and the same statement, while narrating an event, it proclaims a mystery."
Response: It must be said that the author of sacred scripture is God, who has the power not only to use words in expressing himself - men can do that much - but of using things as well. Thus, since words signify something in any science, this science is special in that not only the words but the things signified by the words signify something. The primary signification, through which words signify things, is called the literal or historical sense. That signification whereby things signified by words have themselves also a signification is called the spiritual sense, which is based on the literal, and presupposes it. Now this spiritual sense has a threefold division.
[This phrase in italics was missing in the base file for this texts, and has been supplied from the Dominican Fathers' translation.]
This spiritual sense is itself divided in a threefold way. Paul says, "The Old Law is a figure of the New Law" (Heb. 7:19), and the New Law is, as Dionysius says, "a figure of the glory to come." Moreover, in the New Law the things that are done are signs of what we ourselves should do.
Thus, insofar as things in the Old Law signify things in the New Law, we have the allegorical sense. Insofar as things done by Christ or by those who prefigure Christ are signs of what we ourselves should do, we have the moral sense. Insofar as they signify what is involved in eternal glory, we have the anagogical sense.
Because the literal sense is what the author intends, and because the author of sacred scripture is God who contains all things within his understanding, there is nothing impossible about even the literal sense containing several meanings, as Augustine suggests.
To the first argument, therefore, it must be said that manifold senses do not lead to equivocation or to any other type of ambiguity, for, as was just said, theses senses are not multiplied in such a way that a single word signifies several things, but rather because the things signified by these words can be signs of still other things. Thus no confusion follows from the reading of sacred scripture, for all other senses are founded on the literal sense. From it alone arguments can be drawn, and not from what is said allegorically, as Augustine explains in his letter against Vincent the Donatist. Nor does this fact detract in any way from sacred scripture, for nothing necessary to the faith is said in a spiritual sense which is not explicitly stated in the literal sense elsewhere.
To the second argument it must be said that these three things - history, etiology and analogy - belong to a single literal sense. It is history when, as Augustine explains, something is straightforwardly reported. It is etiology when the cause of that thing is explained, as when God explains why Moses permitted the repudiation of wives, namely because of the hardness of their hearts. It is analogy when the truth of one scripture is shown to be consistent with the truth of another. Among the four, allegory alone stands for the spiritual senses. In the same way, Hugh of St. Victor includes the anagogical sense under the allegorical and enumerates only three senses: The historical, allegorical and tropological.
To the third it must be said that the parabolic sense is included under the literal, for words can signify something properly and something else figuratively. In the latter case, the literal sense is not the figure of speech itself but the thing figured by it. For example, when scripture refers to the arm of God, the literal sense is not that God has a physical limb, but that he has what that limb signifies, namely the power to do things. Thus it is clear that no falsehood can ever underlie the literal sense of sacred scripture.
As to this question, there are three points of inquiry:
Whether God's existence is self-evident
Whether it can be demonstrated
Whether God exists.
Thus we proceed to the first point. It seems that God's existence is self-evident, for those things are said by us to be self-evident the knowledge of which is naturally within us, as is the case with first principles. But, as John of Damascus says, "The knowledge of God's existence is naturally implanted in all things." Therefore God's existence is self-evident.
Furthermore, those things are said to be self-evident the truth of which is obvious once the meaning of the words is clear. For example, when we understand the means of the words "whole" and "part," we immediately realize that every whole is greater than its part. Once we understand the meaning of the word "God," however, it immediately follows that God exists. The words itself signifies "that being a greater than which cannot be signified." That which exists in fact and in the mind is greater than that which exists in the mind alone. Thus, since the moment we understand the meaning of the word "God" he exists in our minds, it follows that he must also exist in fact. Thus God's existence is self- evident.
Furthermore, it is self-evident that truth exists, for whoever denies the existence of truth simultaneously concedes its existence. If truth does not exist, then it is true that truth does not exist; yet if something is true, then truth exists. God, however, is truth itself. "I am the way, the truth and the life" (Jn. 14:6). Therefore God's existence is self-evident.
But on the contrary, no one can think the opposite of what is self-evident, as Aristotle remarks. One can, however, think the opposite of the proposition "God exists," for, as the Psalm says, "The fool says in his heart, 'there is no God." (Ps. 13:1, 52:1). Thus it is not self-evident that God exists.
Response: It must be said that a thing can be called "self-evident" in two- ways, in itself and in relation to us. A proposition is self-evident when its predicate is included in the definition of its subject. For example, in the proposition "man is an animal," the idea of "animal" is included in the definition of "man." Thus if everyone knows the definitions of both subject and predicate, the proposition will be self-evident to all, as is the case with the first principles of demonstration, the terms of which are so common that no one is ignorant of them, such as "being" and "nonbeing," "whole" and "part," etc. If, the proposition may be self-evident in itself, but not to them. Thus it happens, as Boethius says, that some things are common conceptions of the mind" and are self-evident "among the learned only, such as that incorporeal beings do not occupy a place."
I say, therefore, that this proposition, "God exists," is self-evident in itself, since the predicate is the same as the subject. For God is his own existence, as will be seen later. Nevertheless, because we do not know what is involved in being God, the proposition is not self-evident to us, but needs to be demonstrated through those things that are more evident to us though less evident to themselves, namely God's effects.
To the first argument, therefore, it must be said that a general and confused knowledge of God's existence is naturally infused within us, for God is man's beatitude and man naturally desires beatitude. What man naturally desires he naturally knows. This is not to know God's existence specifically, however. It is one thing to know that someone is approaching and quite another to know that Peter is approaching, even though that someone may actually be Peter. Many people think that the perfect good of man called "beatitude" is wealth, some imagine it to be pleasure, and so on.
To the second argument it must be said that he who hears the name "God" may perhaps not know that it signifies "something greater than which cannot be conceived," since some people have thought of God as a body. Granting, however, that someone should think of God in this way, namely as "that being a greater than which cannot be conceived, "it does not follow on this account that the person must understand what is signified to exist in the world of fact, but only in the mind. Nor can one argue that it exists in fact unless one grants that there actually exists in fact something a greater than which cannot be conceived. It is, however, precisely this assertion the atheist denies.
To the third, it must be said that the existence of truth in general is self- evident to us, but it is not self-evident that this particular being is the primal truth.
We proceed thus to the second point. It seems that God's existence is not demonstrable, for it is an article of faith. What is a matter of faith cannot be demonstrable, for demonstration allows one to know, whereas faith, as Paul says, is in "things not seen" (Heb. 11:1). Therefore God's existence is not demonstrable.
Furthermore, the central link in any demonstration is a definition; yet we cannot know what God is, but only what he is not, as John of Damascus says. Therefore we cannot demonstrate God's existence.
Furthermore, if God's existence were demonstrable, this could only be through his effects; yet his effects are not proportionate to him, for he is infinite, his effects are infinite, and there is no proportion between the two. Therefore, since a cause cannot be demonstrated through an effect which is not proportioned to it, it seems that God's existence cannot be demonstrated.
But on the contrary Paul says, "The invisible things of God are understood by the things that are made" (Romans 1:20). Such could not be the case unless God's existence could be demonstrated by the things that are made, for the first thing to be understood about a thing is whether it exists.
Response: It must be said that there are two types of demonstration. One is through the cause, is called a demonstration propter quid, and argues from what is prior in an absolute sense. The other is through the effect, is called a demonstration quia, and argues from what is prior according to our perspectives; for when an effect is better known to us than its cause, we proceed from the effect to knowledge of the cause. In situations where the effect is better know to us than the cause, the existence of the cause can be demonstrated form that of the effect, since the effect depends on the cause and can only exist if the cause already does so. Thus God's existence, though not self-evident to us, can be demonstrated through his effects.
To the first argument, therefore, it must be said that God's existence and other things about him which (as Paul says) can be known by natural reason are not articles of faith but preambles to the articles of faith. For faith presupposes natural knowledge just as grace presupposes nature and perfection presupposes something which can be perfected. Nothing prohibits what is demonstrable and knowable in itself from being accepted on faith by someone who does not understand the demonstration.
To the second it must be said that, when a cause is demonstrated through its effect, the effect substitutes for the definition of the cause within the demonstration. This is particularly true in arguments concerning God. When we prove that something exists, the middle term in the demonstration is what we are taking the word to mean for purposes of the demonstration, not what the thing signified by the word actually is (since the latter, the actual nature of the thing in question, is determined only after we determine that it exists). In demonstrating that God exists, we can take as our middle term definition of what this word "God" means for us, for, as we shall see, the words we use in connection with God are derived from his effects.
To the third, it must be said that perfect knowledge of a cause cannot be derived from an effect that is not proportionate to the cause. Nevertheless, the existence of the cause can be demonstrated clearly from the existence of the effects, even though we cannot know the cause perfectly according to its essence.
Thus we proceed to the third point. It seems that God does not exist, for if one of two contrary things were infinite, its opposite would be completely destroyed. By "God," however, we mean some infinite good. Therefore, if God existed evil would not. Evil does exist in the world, however. Therefore God does not exist.
Furthermore, one should not needlessly multiply elements in an explanation. It seems that we can account for everything we see in this world on the assumption that God does not exist. All natural effects can be traced to natural causes, and all contrived effects can be traced to human reason and will. Thus there is no need to suppose that God exists.
But on the contrary God says, "I am who I am" (Ex. 3:14).
Response: It must be said that God's existence can be proved in five ways. The first and most obvious way is based on the existence of motion. It is certain and in fact evident to our senses that some things in the world are moved. Everything that is moved, however, is moved by something else, for a thing cannot be moved unless that movement is potentially within it. A thing moves something else insofar as it actually exists, for to move something is simply to actualize what is potentially within that thing. Something can be led thus from potentiality to actuality only by something else which is already actualized. For example, a fire, which is actually hot, causes the change or motion whereby wood, which is potentially hot, becomes actually hot. Now it is impossible that something should be potentially and actually the same thing at the same time, although it could be potentially and actually different things. For example, what is actually hot cannot at the same moment be actually cold, although it can be actually hot and potentially cold. Therefore it is impossible that a thing could move itself, for that would involve simultaneously moving and being moved in the same respect. Thus whatever is moved must be moved by something, else, etc. This cannot go on to infinity, however, for if it did there would be no first mover and consequently no other movers, because these other movers are such only insofar as they are moved by a first mover. For example, a stick moves only because it is moved by the hand. Thus it is necessary to proceed back to some prime mover which is moved by nothing else, and this is what everyone means by "God."
The second way is based on the existence of efficient causality. We see in the world around us that there is an order of efficient causes. Nor is it ever found (in fact it is impossible) that something is its own efficient cause. If it were, it would be prior to itself, which is impossible. Nevertheless, the order of efficient causes cannot proceed to infinity, for in any such order the first is cause of the middle (whether one or many) and the middle of the last. Without the cause, the effect does not follow. Thus, if the first cause did not exist, neither would the middle and last causes in the sequence. If, however, there were an infinite regression of efficient causes, there would be no first efficient cause and therefore no middle causes or final effects, which is obviously not the case. Thus it is necessary to posit some first efficient cause, which everyone calls "God."
The third way is based on possibility and necessity. We find that some things can either exist or not exist, for we find them springing up and then disappearing, thus sometimes existing and sometimes not. It is impossible, however, that everything should be such, for what can possibly not exist does not do so at some time. If it is possible for every particular thing not to exist, there must have been a time when nothing at all existed. If this were true, however, then nothing would exist now, for something that does not exist can begin to do so only through something that already exists. If, therefore, there had been a time when nothing existed, then nothing could ever have begun to exist, and thus there would be nothing now, which is clearly false. Therefore all beings cannot be merely possible. There must be one being which is necessary. Any necessary being, however, either has or does not have something else as the cause of its necessity. If the former, then there cannot be an infinite series of such causes, any more than there can be an infinite series of efficient causes, as we have seen. Thus we must to posit the existence of something which is necessary and owes its necessity to no cause outside itself. That is what everyone calls "God."
The fourth way is based on the gradations found in things. We find that things are more or less good, true, noble, etc.; yet when we apply terms like "more" and "less" to things we imply that they are closer to or farther from some maximum. For example, a thing is said to be hotter than something else because it comes closer to that which is hottest. Therefore something exists which is truest, greatest, noblest, and consequently most fully in being; for, as Aristotle says, the truest things are most fully in being. That which is considered greatest in any genus is the cause of everything is that genus, just as fire, the hottest thing, is the cause of all hot things, as Aristotle says. Thus there is something which is the cause of being, goodness, and every other perfection in all things, and we call that something "God."
The fifth way is based on the governance of things. We see that some things lacking cognition, such as natural bodies, work toward an end, as is seen from the fact hat they always (or at least usually) act the same way and not accidentally, but by design. Things without knowledge tend toward a goal, however, only if they are guided in that direction by some knowing, understanding being, as is the case with an arrow and archer. Therefore, there is some intelligent being by whom all natural things are ordered to their end, and we call this being "God."
To the first argument, therefore, it must be said that, as Augustine remarks, "since God is the supreme good he would permit no evil in his works unless he were so omnipotent and good that he could produce good even out of evil."
To the second, it must be said that, since nature works according to a determined end through the direction of some superior agent, whatever is done by nature must be traced back to God as its first cause. in the same way, those things which are done intentionally must be traced back to a higher cause which is neither reason nor human will, for these can change and cease to exist and, as we have seen, all such things must be traced back to some first principle which is unchangeable and necessary, as has been shown.