The Dominican who began the trend toward an Aristotelian Christianity was Albert the Great. He followed in the tradition set by the Moslem philosophers. But it is Thomas Aquinas, his most famous pupil, who is credited with coming closest to bringing Christianity and Aristotelianism into line. First, in line with what the Moslem philosophers had been doing Thomas established the distinction between the realms of philosophy and theology.

The diversification of the sciences is brought about by the diversity of aspects under which things can be known. Both an astronomer and a physical scientist may demonstrate the same conclusion, for instance that the earth is spherical . . . Accordingly there is nothing to stop the same things from being treated by the philosophical sciences when they can be looked at in the light of reason and by another science when they are looked at in the light of divine revelation.

Thomas added that some truths, though they are accessible to reason, have been revealed nevertheless so that those who are ignorant may know them. The human mind, he said, is weak and easily confused so its conclusions are not absolutely certain. Thus though he taught that philosophy is a science that can reach to the very limits of human reason, he never implied that it was infallible. Furthermore, not all men have the exceptional intellectual gifts required to reach its highest conclusions. Theology, on the other hand, studies truths that have been revealed and therefore cannot be doubted. Though many of these beliefs are beyond the reach of reason, they do not contradict it. This attitude, of course, was a direct response to Averroes and the Latin Averoists who dominated the secular schools at the University of Paris, who claimed there were two sets of truths, those developed through reason, and those developed through revelation. It was not necessary that these both be compatible. It was an answer also to the followers of Aviccena who said that truth through reasoning was superior to that obtained through revelation. For our purpose what matters is that it confirms the belief that set western culture apart from all others, that the world is rational and that it can be know through reason. That reason itself can and does transcend the intellectual power of man in fact confirms rather than disputes this claim. It is through this intellectual power that man transcends the animals.

As you may recall, Aristotle's concept of soul a the form of a living thing prevented the soul from being immortal in the sense that Christians and Moslem theology implies. The Moslem philosophers were not really successful in adapting the Aristotelian concept of soul to that of the Koran. But Aquinas offered a brilliant answer to this problem in his Summa of Theology.

For the Soul is the first principle of our nutrition, sensation, and locomotion, as it is of our understanding. so, whether we call this principle by which we primarily understand the intellect or the intellectual soul, it is the form of the body. But anyone holding that the intellectual soul is not the form of the body must first explain how it happens that this action of understanding is the action of this particular man, since each one is aware that he himself is understanding. ...This particular man understands because his form is the intellectual principle.

Aristotle's intellectual soul, or mind, was not connected to the body and thus did not cease to exist when the body ceased to exist. However, it does not begin to exist until a man begins to think. Thus, like the Christian and Moslem concept of soul, it is born with the individual man but continues to exist after the destruction of the body. This created a direct link between the form of the body as an intellectual principle and the body itself as a physical entity. Understanding the importance of this link is crucial to understanding Aquinas' approach to God through his effects as witnessed by physical as well as intellectual entities.

That is why Aquinas' five proofs of the existence of God hold the potency they do. But we should examine these proofs in the light both of the evolution of western culture and in context with Aquinas' world. Remember, he was attempting to change the approach to knowledge that had been ingrained into Christian philosophy. In particular he had to reject the extreme platonistic views that made God either self-evident, or an article of faith. God, to be meaningful to him, must be known through experience. Through what exists in the sensual world. But most important he did believe that the existence of God could be proved.

Any attempt to prove God's existence seems useless to those people who claim that there can be no argument about a self-evident and indemonstrable truth when the contrary is an intellectual impossibility. .. .

Their conviction comes from custom. From childhood men are accustomed to hear and call upon the name of God. Now, custom becomes second nature. especially when it has influenced us from an early age, doctrines early imparted come to be accepted without question. Moreover, what is evident in itself can be confused with what is evident to us... There are others who also declare that any attempt to prove God's existence is useless, but for very different reasons. Affected by the weakness of the arguments often offered, they declare that this truth cannot be discovered by reason. According to them, an act of faith in divine revelation is needed.

Thus, the problem of a proof of the existence of God must begin with the idea that he can be known through his effects in the world around us.

There can be two procedures in demonstrating anything: one is through the cause, and is called proof for-the-reason-that; this kind of demonstration begins with what is prior in reality. The other takes place through an effect, and is called a proof insofar-as; and this kind of argument begins with what is first apparent. When any effect is better known to us than its cause, we proceed from knowing the effect to knowing its cause. Beginning with an effect. we can demonstrate the proper cause of its being as long as the effect is more evident, since if the effect exists, the cause must pre-exist, inasmuch as every effect depends on its cause. And thus, insofar as God's existence is not self-evident to us, it can be demonstrated by us by beginning with those of his effects that are known to us.

So, if something exists, then the cause for it necessarily exists. From this beginning we can proceed to discover the cause from an examination of the effect. But if we are attempting to prove the existence of something we must have a method by which we can determine a things existence from knowledge of its effects. Because every effect must have a cause so we can prove by an examination of its effects that something exists.

Existence can be understood in two senses, one signifying the actuality of being and the other signifying the affirmative judgment made by the mind, which joins subject to predicate. In the first sense, God's existence can be known no more than his essence can; but in the second sense we may be able to know that the proposition we form, namely. that he exists, is true.

Thus, if we are to understand the existence of something that can only be known through its effects, then it must be the kind of knowledge that comes from judgements made concerning ideas in the mind. Ideas, however, that must be derived from sensible objects. For in a true Aristotelian view of the world , the only things we know through experience are those things that we detect through our senses.

Nor does it result, as the first argument claimed, that as soon as the significance of the word "God" is understood, we know that God exists. First, because not all know, even those who agree that there is a God, that God is that reality than which no greater can be thought, since there were many ancient thinkers who asserted that this world is God. Nor from the significance of the word "God" as taught by Damascene can such conclusions come. Second, because even allowing that everyone understands this word "God" as signifying something than which no greater can be thought, it doesn't follow that something than which no greater can be thought does exist in reality. For a thing exists just as its name signifies. Now. from the fact that we understand intellectually what the word "God" is intended to signify. nothing follows except that God is in the intellect. Therefore it will not follow that the reality than which nothing greater can be thought is elsewhere than in the intellect. And hence it does not follow that there exists in reality something than which no greater can be thought. And so this is no argument against those who state that God does not exist, since nothing prevents someone from thinking of some greater thing, unless it be stipulated that there is in reality something than which no greater can be thought....

Again, just because we may think that God does not exist, we may not conclude that we can therefore think of something greater than God. For we can think that God does not exist not because of any imperfection in his being or any uncertainty connected with it, since his being is in itself supremely evident, but because of the weakness of our intellect, which can know him not in himself but in his effects, and thus by reasoning it comes to know that he exists.

And this also answers the third argument. For just as it is self-evident to us that a whole is greater than its part. so to those who see the very essence of God, it is most evident that God exists. since his essence is his existence. But since we cannot see his essence, we come to know his existence not in himself but in his effects.

This shows Aquinas at his most Aristotelian. It also shows the degree to which his approach represents a major changing in the world-view of the Western Culture of the thirteenth century.

Our position is also challenged by some whose opinion would render useless the effort of those trying to prove that God exists. For they assert that by reason we cannot discover that God exists, and that such knowledge is had only through faith and revelation. Some were moved to assert this because of the poor arguments used by some people to prove God's existence. Quite possibly but falsely, this error might be grounded upon the statements of some philosophers who demonstrate that essence and existence are the same in God, namely, the answer to the question, "What is he?" is the same as the answer to the question. "Is he?". Certainly we cannot by any reasoning~ process come to the knowledge of what God is. It will appear therefore impossible to prove by reason whether God is.

Remember that we are discussing this from a very Aristotelian standpoint. When Aristotle taught his logic to his students he taught them two different uses for it. One was what he called "dialectic". When logic is used in this sense the statements used as premises can be true or false but they are assumed by the logician to be true. The only thing that can be proved through dialectic conclusively is the inner consistency of the set of logical arguments. One can accept the premises as true and thus be convinced that the conclusion is true. Or one can reject the premises and make the argument futile. The object of dialectic is persuasion, to convince others of something you assume to be true even though you have no direct proof.

The second application of Aristotle's logic was called demonstration. In a demonstrative argument the premises must either be first principles, that is premises that no one would doubt, or premises that have been developed through prior demonstrative arguments. Thus valid demonstrative arguments always lead to true conclusions which cannot be rejected. Therefore, if we want to prove something conclusively we must use demonstration and not dialectic. But demonstration demands premises that are either first principles or derived from first principles. God's essence, however, is ineffable. Therefore it cannot be known conclusively. Thus we are forced to prove the existence of God through what we can know conclusively, his effects in the sensual world.

Again: If. according to the philosopher's system, we must begin with a name's significance to prove whether the thing exists, and since according to the philosopher (Metaph. 4) a name's significance is its definition, without knowledge of the divine essence or quiddity, we have no means to prove God's existence. Again: if the Principles of demonstration are made known to us originally through the senses, as is shown in the Posterior Analytics I:18. whatever is beyond sense and sensible objects is apparently unprovable. But such is God's existence. Therefore it cannot be proven. The error of this view is first seen by the art of demonstration, from which we learn to conclude causes from effects; second, by the very order of the sciences. For, if no substance beyond sensible substance can be an object of knowledge, there will be no science above Physics.... third, by the efforts of the philosophers who have tried to prove God's existence; fourth, by the truth of the Apostle who asserts (Rom. 1: 20) : "the invisible things of God are clearly seen, being understood by the things that are made." Nor should we be affected by the contention of the first argument that essence and existence are the same in God. For this should be referred to the existence by which God subsists in himself, and of this kind of subsistence we are ignorant as we are of his essence. But it does not refer to the existence signified by intellectual judgment, for we can prove the existence of God in this way as when by demonstrative arguments our intellect is led to form the proposition affirming that God exists.

In Syllogistic logic it is the middle term, that term that is found in both premises and not in the conclusion, that links the two premises together and leads to the implication of the conclusion. But this middle term too must be something we can have direct knowledge of. But the essence (quiddity) of God is something we cannot know directly. therefore we are forced to utilize the effects of God to determine the proof of his existence because only these can be known.

In addition: We need not use the divine essence or quiddity as the middle term when we argue to prove God's existence, as supposed by the second objection; but in the place of the quiddity as middle term we take his effects, as is done in a Posteriori reasoning, and from these effects we get the significance of this word "God," for all the divine names are derived either from the difference between God's effects and himself or from a certain relationship between his effects and God.

Likewise it is obvious from the fact that. although God transcends all sensible things and senses, yet his effects, from which we derive the proof of his existence, are sensible things. And so our knowledge originates from the senses. even when it is knowledge of things transcending them.

If there can be no contradiction between reason and revelation, that is, if it possible to know through reason what is known through revelation, then knowledge through revelation presupposes knowledge through reasoning. Though the reasoning may in fact be beyond the ability of man, yet that reasoning must be possible. Two points are being made here. First that what is known through faith is rational, that is it is capable of being known through reason. And second, that if one knows something to be true through faith then it is not necessary for him to determine its truth through reasoning for such is presupposed.

The fact that God exists and similar truths about him that are knowable by strict reasoning are not articles of faith, but preambles to them. Just as grace presupposes nature, and perfection presupposes the capacity for perfection, so faith presupposes natural knowledge. Yet nothing stops any man from accepting as an article of faith something that can be scientifically known and proven, although perhaps not by him.

Aquinas is not attempting to place reason above faith or revelation. What he is doing is making a strong case for the viability of reasoning as one path toward knowledge of God, though not the only one.

Next Aquinas explained Aristotle's four causes in a very thirteenth century way. This is important because his five proofs for the existence of God argue from knowledge of his effects in the world. That is effects that are obvious in the same way that Aristotle's first principles are obvious, to the necessity of Gods existence. For this he wanted to make sure that we have a clear concept of what is meant by cause and effect.

Aristotle names the kinds of causes and reduces them to four types. He notes first that cause means the immanent matter within which anything comes to be and that exists within it. This he says in order to emphasize its difference from privation or a contrary state from which something is said to originate but that does not stay within, as when something white is made from something black or nonwhite. But whenever any statue is fashioned from bronze or a cruet from silver, these materials are within the product, for bronze is not eliminated by statue nor silver by cruet. These things are material causes.

Second, cause refers the form or structure or type of a thing. Such is the formal cause. and it brings about an effect in two ways: either as an intrinsic form (when it is called a specific form). or as the extrinsic form after whose likeness the thing is fashioned, and in this way the exemplar of a thing is called its form, which accounts for Plato saying that ideas were forms. The genus and species of anything that the definition of its nature states is determined by the form. Hence the form that is what the Aristotelian "what it was for it to be" means is that which determines what a thing is, for me definition, although it includes the material parts. emphasizes the form.

Third, cause signifies the first principle of change and of rest when it is the moving or efficient cause. Aristotle speaks indiscriminately of change and rest, for natural motion and rest are related to the same cause as are violent movement and forced rest. He cites two instances: of the adviser whose counsel causes a certain policy, and of the father who is cause of his child; these include the two principles of efficient motion, namely, will and natural determinism. Generally speaking, all makers are causes of what is made, and all changers of changing things. That is rightly classified as an efficient cause when it makes anything in any way in regard to substance or accidents. Aristotle links maker with changer; the former is the cause of a thing, the latter of its becoming.

Fourth, cause signifies the aim, that for the sake of which something is. Health, for example, is the cause of going for a walk. The question, "Why" expects a cause. And this involves not only the ultimate aim for which the efficient cause acts but likewise all the intervening means.

The Aristotelian approach to causation makes it possible for one to follow the implications from effect back to cause. The Platonic view had no use for causation. Therefore it had never been applied by anyone prior to Aquinas. Since in a Platonic sense, coming to be is simply a matter of participating in a set of forms, or in an Augustinian sense a set of exemplars in the mind of God, causation is not a problem. But there is a difference between the cause of something coming to be and that of something persevering in existence, as we can see by this next quotation.

An effect depends upon its cause only insofar as that is its cause. We should note that a cause may be a cause of the coming of the effect and not directly of its existing. We can find examples both in artificial and natural events. A builder causes the construction of a house but not the house that endures; that it caused by the consistence of the components. Any efficient principle that is not the cause of a natural form in itself is the cause of a becoming; it is not the direct cause of the resulting thing. With two things specifically identical, one cannot be the direct cause of the other's specific form, since they are therein identical. But one may be the cause of the other's coming to be in this or that definite matter, as when one man generates another. In other words, it is the cause of a becoming.

But whenever an effect comes from any cause different in nature, the latter may then be the cause of form itself and not merely of its coming into such matter. In that case it will be the cause of a being. not merely of a becoming. Just as the becoming of a thing must end when the action of its cause ceases, the being of a thing cannot endure when the action of its cause has ceased.

Aristotle's argument for a first mover is highly dependent on Aristotle's concept of motion as change of any kind, not of causation. Aquinas adapted the argument to show that God, or the principle mover is necessary in his sense of all motion as being caused.

Since anything moved by another is a sort of instrument, all things in motion would be instruments if there were no first mover. Moreover, if there were an infinite series of movers and things in motion and yet no first mover, all these infinite movers and things moved would be instruments. Even without any specialized knowledge we can realize what is ridiculous in the notion of any instrument that is not put into motion by a principal: this would be like saying that a saw or ax but no workman was at work in the making of a bed or ches

We must be clear, however, that although Aquinas uses the term mover in a special sense that is not as broad as Aristotle and different from Plato, he does not thereby imply that they are talking about different things..

It should be noticed that Plato. who speaks of movers in motion (Phaedrus, 245c; Laws, 893b-896b) understands the term motion in a wider sense than does Aristotle, who keeps to its restricted sense of a potential act of a subject in potentiality, which applies only to quantified and material reality (Physics, 201). Whenever Plato speaks of anything not a body moving itself, for him this motion includes such actions as understanding and thinking. In other places Aristotle likewise speaks this way, as when he speaks of the first mover moving itself by understanding and willing and loving itself (De Anima, 433b15). There is no contradiction here, for it comes to the same thing whether with Plato we come to the first being, which moves itself, or with Aristotle to the first being, which is wholly immutable.

Still, since Aristotle's argument for the necessity of a first mover depends on final causes, love is the purpose for which the initial movement is caused, it won't quite do for Aquinas' argument from effects. Therefore, it was necessary to shift the emphasis to efficient rather than final causes.

An infinite series of efficient causes in essential subordination is impossible. The causes that are essentially needed to produce any definite effect cannot therefore be multiplied infinitely, as though a block could be lifted by a crowbar, which in its turn is levered by a hand, and so on to infinity. But an infinite series of causes accidentally subordinated is not considered impossible as long as the totality of causes thus multiplied are assembled as one cause, with their multiplication as incidental to the causality at work. A blacksmith, for example, may operate with many hammers because one after another breaks in his hand, but that any one hammer be used after another particular one is incidental.

It is appropriate to divine providence to utilize things according to their manner of being. The action of anything follows its form, which is the principle of action. Now. a voluntary agent acts through no definite form, inasmuch as the will acts when a form is apprehended by the intellect, since the apprehended form objectively moves the will. But there is no definite form of any effect in the intellect, which naturally understands a multitude of forms, and thus the will can Produce a plurality of effects. It is not, therefore, appropriate for divine providence to exclude freedom of the will.

Thus, we find that Aquinas has taken the arguments for the existence of God made by essentially Platonic-Augustinian philosophers, and converted them into his own brand of Aristotelianism. This first proof deals with the necessity of a first mover. It is reminiscent of Aristotle's uncaused cause. However, even Aristotle did not begin with sensual entities, in every case Aquinas was arguing from what we sense in the world to what must exist. As you may recall Aristotle's argument was made almost entirely in a universal language.

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 actuality. ... 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.

As Aristotelian as this might sound, when we compare it with Aristotle we find more very important differences that highlight the changes that developed through 1600 years of evolution. Since for Aristotle causation was a category of movement, he used the terms not arbitrarily but as part to whole. Aquinas' description begins and ends with physical movement in the sensory realm. Aristotle's uncaused cause was love, or the cause of the desire that moves the will, thus it is not physical. That movement existed in the sensual world was obvious to both, but Aristotle was trying to prove not only the existence of the prime mover, but of the necessity of its existence. Aristotle said that the potentiality to move was not enough because then it would be possible that nothing might have come into existence. In his discussion of the impossibility of an infinite series of efficient causes he showed that a case for a necessary being as the source of all movement could be made from knowledge of existing motion. Don't forget that the thirteenth century world of Aquinas was a secular world where people deal with what they find in the world around them. Ptirim Sorokin described the period leading to the renaissance and that leading to Classical Greece in similar terms, meaning by this that they both exhibit the same characteristics. But by that he meant fifth century Greece, the world of Parmenedes and the Athens of Anaxagorus and the young Socrates, not that of Aristotle.

The second way is the deals directly with efficient causes. Note again that this argument is grounded in the sensual world.

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, not 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 God.

A statement like this could never have been made in a Greek context. Though he might have gotten his cues from Aristotle his clear intent was to show the necessity of God through effects in the sensual world. That such an attempt was necessary is a strong indication of the trend toward sensual reality that the west had taken as we get into the late middle ages. The next proof takes into the realm of nature.

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 thee 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 things 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 already been 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.

This argument is drawn from Avicenna's proof of God through his concept of possible being as a mode of being. The argument itself has been put simply that if anything exists then it is necessary that something exist. But it was Avicenna who originally used the concept of possible being to back the argument up. This brings home a very important assumption concerning the idea of a rational world. Because this is a rational world, it is not possible that it came into existence simply through the whim of the gods or nature. Only Democritus and the atomists claimed that the world was created by chance. Even Einstein agreed when he said that God does not play dice with the universe. To consider a world derived through chance would imply to most that anything could occur by chance thus there would be no rationality to the universe. Aristotle's fourth and final cause was the reason for something's existence. Love as the force that causes desire initiates the sequence of fourth causes. for Aquinas God was the actuality that provided the cause that translates from possible existence to actual existence. God, for him, was the author of being. The fourth and fifth ways, though they may remind us of more recent sources, date back before Socrates and are actually platonic in character since they infer comparison to a standard beyond the sensual world.

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 is written in Metaph. ii. Now the maximum in any genus is the cause of all in that genus, as fire, which is the maximum of heat, is the cause of all hot things, as is said in the same book. 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 from the governance of the world. We see that things that 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 we call God.