God, Proofs for the Existence of

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The classic text presenting proofs for the existence of God is that of St. thomas aquinas (Summa theologiae 1a, 2.3). Known as the quinque viae or "five ways," these demonstrations are proposed by Aquinas as a foundation for his systematic development of sacred theology. This article analyzes the arguments of each of the five ways, prefacing this by an introduction that explains the need for the proofs, the methodology that underlies them, and the general characteristics of the line of their argument.


Many feel that man's innate desire for happiness, which can be only satisfied in God, makes sufficiently evident the existence of God. Although God truly implants this desire in man, the fact is that many men do not seek their happiness in God. Hence, this desire for happiness of itself is too vague to evince conclusively and clearly the existence of God (Summa theologiae 1a, 2.1 ad 1). The same must be said to those who hold that the existence of truth, which in general is self-evident, makes God's existence obvious (ibid. ad 3). Men, particularly in recent times, have frequently rejected the proposition that God exists, which could not be the case if the statement were immediately evident.

Need for proof. A self-evident proposition is one wherein "the predicate forms part of what the subject means" (Summa theologiae 1a, 2.1). "God exists" is such a proposition in itself since the divine essence and existence are identical. Yet, the statement is not self-evident to the human intellect because man does not grasp the divine nature as such. Clear-cut evidence of God's existence is so apparently lacking that the genuine problem concerns whether His existence can in any way be shown.

On the other hand, God's existence is not so deeply embedded in mystery that only faith can make it known. Rather, God's existence is attainable through the natural powers of human reason and is a presupposition to revealed truths (Summa theologiae 1a, 2.2 ad 1). In other words, both philosophy and theology may ask the question of God's existence. Philosophy asks the question in the supreme branch of natural wisdom called metaphysics and does so in order to discover the principles of its own subject matter, being in common (ens in commune ). In theology the question is asked to ascertain whether the science has a subject matter at all. Whereas philosophy terminates its investigations of truth by arriving at God, theology initiates its study with God and uses revealed principles as it analyzes all of reality.

Since the five ways are found in a treatise that is theological and not philosophical, to expect the proofs as given in the Summa by St. Thomas to expound the full metaphysical implications would be to confuse theology with philosophy. Yet the five ways are truly proofs; "way" is not meant to indicate some weak expression, but rather the strong work of the theologian in his rational approach.

The five ways are meant to be demonstrations of the conclusion: God exists. Demonstration is needed when some fact or truth is not evident. Proving the obvious is not merely a waste of argument but quite impossible. God's existence is not obvious. The danger seems to be that the supposition of His existence is so remote and beyond man's intellectual capabilities that no method can be found to establish it. The difficulty would be insurmountable were the proofs to go beyond the fact that God exists. Once an attempt is made to investigate the very nature of God, the limits of the proofs for His existence are exceeded.

Methodology. The question, then, is not why God exists, which rationally cannot be asked, but whether or not God exists. St. Thomas follows an Aristotelian methodology based on the Greek philosopher's logic, physics, and metaphysics. Having answered affirmatively the question whether God's existence is demonstrable, St. Thomas presents the five ways.

demonstration is a categorical syllogism that intends to produce certain knowledge. This syllogistic device employs a middle (or connecting) term to establish the fact that a designated predicate belongs to the subject under consideration. This middle term, called the medium of demonstration, is a definition. If the definition is based on one of the four causes, the demonstration is a priori in the sense that it gives the reason or cause why the predicate can be said of the subject. Clearly demonstration of this kind is impossible relative to God, who is beyond definition, exceeding as He does all human categories of thought.

Instead, the demonstration must be a posteriori; it must proceed from effect to cause and employ a nominal definition rather than a causal one. In the present consideration an effect serves as a nominal definition of the cause. St. Thomas concedes that the effect is by no means proportionate to the cause; yet, no difficulty arises since the only point the proof intends to establish is the existence of the cause (Summa theologiae 1a, 2.2 ad 3). For example, one who detects a fragrance need not know what the nature of the odoriferous object is in order validly to conclude that some fragrance-giving thing does exist. One author (O'Brien) suggests a brief outline of the demonstration of the first way as follows:

God is the First Unmoved Mover (nominal definition imposed from movement); But the First Unmoved Mover exists (effect, movement demands this); Therefore God exists.

General Characteristics. All five ways begin with evidences of sense experience that are effects, as it develops, of God. Basic to the cogency of the proofs is the fact of limitation within the actualities studied, a concretion of act and potency that means dependence and thus leads to an independent being free of potency in any form. The first, second, and fifth ways consider the world of operation: motion, efficient causes, and finality. The third and fourth ways start from the actuality of being and show its extremes of contingent and necessary, and of more and less good, true, or noble.

Since all the proofs deal with effects, the notion of efficient causality is present not only in the second, as is obvious, but also in the other four. Nevertheless, in the resolution of each proof, the particular effect leads to a determined actuality of the cause that alone adequately explains the effect. The five ways are therefore truly distinct, not mere variations of one proof.

Each proof terminates in a cause that alone sufficiently explains the effect used as the middle term of the demonstration and as the nominal definition of God. In particular, this means that (1) motion is explained only by a mover not subject to motion; (2) subordinated causes are intelligible as causing only if there is a cause that is uncaused; (3) the possible or contingent must depend on a cause not merely necessary, but with no cause of its own necessity; (4) graded perfections are limited perfections, and only an unlimited perfect cause could be responsible for them; and (5) directed things moving toward determined ends depend on an intelligent ruler. In each way the crux of the proof lies in the truth that the cause reached produces a formality in the effect that the cause itself transcends. If this were not the case, the problem would still remain for solution.

Two observations from the commentary of cajetan on the five ways are worthy of mention. Although each proof establishes a predicate that in truth is proper to God, the proof as presented in this theological context merely establishes the need of a first mover unmoved, a first efficient cause uncaused, etc., without caring what else can be said of its nature. Secondly, the direct conclusion of the five ways is simply "God exists" and not "God as God exists," for the latter assertion would exceed the premises; each way concludes to the proper cause of the effect adopted as the middle term, but God as God is much more than that.

Proof from Motion

The point of departure is the fact of experience that motion exists. "The senses clearly perceive that some things in the world are being moved." Local motion is the most obvious, although as the proof unfolds, every motion or change in its totality is embraced, that is, any transit from potency to act. Were the proof restricted to physical movement, the demonstration could stop at some physical first mover. Yet any going from potency to act constitutes a real change and so falls within the definition of motion.

Argument. The force of the proof rests on the nature of motion as an incomplete act, an actualization of what is potential. Unless motion is understood to be a dependent actuality requiring something else already in act to explain it, the cogency of the proof is lost. The argument depends upon the Aristotelian concept of motion and its corollary, "Whatever is being moved is being moved by another." Also rooted in the proof is the doctrine of potency and act (see potency and act). Nothing can be at the same time in potency and in act relative to the same reality, and consequently nothing can reduce itself to act in respect to that potentiality. To do so would be a contradiction. To produce motion is to give act, but nothing can give what it does not possess. Hence, the mobile thing cannot produce its own motion; it cannot give itself the very act it lacks, for otherwise it would not be in potency to it.

Motion is an effect that depends intrinsically on a cause. In other words, without the cause here and now causing, the motion would not exist. Thus the proof is not considering a motion given independent existence, as when one man generates another and he in turn generates a third, and so on. The father can die and his son continue to live and even generate, for the dependence here is accidental, limited to communicating the original viable material for conception within the mother. An immediately subordinated motion, on the other hand, ceases with the cessation of the prime mover; for example, "if the hand does not move the stick, the stick will not move anything else." In moved movers an infinite regress is repugnant. St. Thomas succinctly states his reasons: "We must stop somewhere, otherwise there will be no first cause of the change, and, as a result, no subsequent causes."

The conclusion of the proof is that a first mover exists who is not subject to change but who is the source of all motion: and in the time of St. Thomas, at least, "all understand this to be God." The causality of the first mover is necessary for every motion that occurs; for whatever may seem to be an ultimate mover within some frame of reference is itself also subject to the definition of motion and thus in the end is dependent on another mover.

The first mover must be completely above the limitations of motion. If not, the problem would still remain. From the first mover comes the act that is responsible ultimately for all motion here and now occurring. To appreciate the implications of the first way, as conceived by St. Thomas, the first mover has to be viewed as the principal agent of motion; all other agents are secondary. The divine causality of motion is seen as universal and necessary, and the prime mover is but one since He is pure act, devoid of the potency that makes for multiplicity.

The first proof does not rest on this or that motion, but treats of motion in itself as something that by nature depends on a cause. Consequently, the proof from motion does not depend on the positive physical sciences, which deal with particular cases and kinds of motion. Difficulties raised against the proof on the basis of positive science should, of course, be faced; but they can be given more adequate treatment under a separate heading (see momion, first cause of).

Difficulties. At this point, it may be useful simply to mention a few common difficulties, most of which pertain to the other ways as well as to the first. One such objection is based on a misconception of what is being proved. It is asked: Why not arrive at a finite being? Why could there not be many unmoved movers? Why is not nature itself a sufficient answer to motion? These questions are really not concerned with the fact of the existence of God, but attempt instead to discuss the nature of God. In the theological context of the proofs, St. Thomas takes up the question of God's nature immediately after establishing his affirmative answer to the question of God's existence. In metaphysics, on the other hand, these objections would be ridiculous; they would indicate that the philosopher had not even reached the heart of the problem concerning the principles of his science. Finitude, multiplicity, and a self-contained reality themselves encourage the quest for a more profound solution.

A second series of difficulties claims that the proofs are arbitrary. If everything requires a mover, why contradict that statement by concluding to an unmoved mover? Or if everything has a cause, why does not God need a cause? These objections arise from an inaccurate reading of the proofs. The first way maintains that whatever is being moved is being moved by another; in no way does it claim that everything must be in a state of being moved. The second way, as will be noted below, is not a study of causality as such, but is restricted to the order of efficient causality.

Thirdly, a most frequent difficulty is that if God is outside nature, that is, completely unlike it, man has no way of knowing Him. Knowledge based on nature would be insufficient, inadequate to attain the supranatural. In reply it has to be said that all knowledge of God is analogical. analogy is an intellectual construct whereby the human reason touches, at least in some way, on areas of reality otherwise closed to it. Thus man's very intellect is not an observed organ as is his eye. As a result, philosophers employ analogy to make evident something of the operations and even the nature of the intellect by comparing it to the functions of the better-known eye. A man says he "sees" a truth; and by this he means thatjust as his eye perceives its object after its fashion of knowing, sense knowledgethe mind comprehends its object in its proper mode, intellectual knowledge. Thus to talk of God's existence does not mean equating the finite existences of beings known in the universe to God's existence; it means, rather, that as existence is a perfection found in a limited way in things, it is also found in an unlimited way in God. Man talks, writes, and thinks of God in this dark manner called analogy. Even faith does not remove analogy.

Finally, a word of caution may save time and prevent confusion. The first way concludes eventually to the truth that God is always involved in the reality of motion. However, to pick out a falling leaf and ask how God is immediately implicated in its motion is to ignore the world of secondary causes also at work. Further, particular mobile things do not yield certitude in and of themselves. For incontrovertible truth, the universal and necessary are required. Demonstration takes its initial step at the sense level, but has to soar high above this level to produce a stable body of certain knowledge.

Proof from Efficient Causality

Once again St. Thomas appeals to the evidence of experience wherein men find an order of efficient causes in the things they observe. No claim is made that every cause must have a cause. In fact, the consideration of efficient causality is made not in any way whatsoever, but precisely under the aspect of the order among such causes discovered in reality. Although this activity is evident to the senses, the intellect must reason over it and comprehend its meaning to give the proof metaphysical depth.

Argument. Two important truths are prerequisite to the proof. The first is that nothing is its own efficient cause, either in being or in operating, since this would involve a contradictionthe thing would be prior to itself, in order to cause itself to be or to operate. The second is that in an ordered arrangement of efficient causes, an infinite regress is impossible. When efficient causes are in an ordered series, one cause is the cause of the next; thus, were the first or an earlier or middle cause removed in the series, the final effect also would be removed. If there were no first efficient cause, no middle efficient causes would be communicating their act, and thus no effects would be produceda condition that man's senses clearly perceive as false. One need but think of a mechanical device such as an automobile to see the implications of efficient causality operating in a subordinated series; or one can look within himself for endless examples of subordinated efficient causality. For instance, each man is the cause of his own speaking, and this involves his intellect, will, brain, nervous system, emotions, vocal cords, mouth, and tongue. Remove the first efficient cause and none of the middle causes will function; consequently no effect will result. While the effect is being produced, it should be noted, the entire series of causes is operating.

An observation of Cajetan can be added for clarification. An intermediate cause must be under the influence of the first cause; otherwise the full efficacy of the inter-mediate cause is lacking. The intermediate cause is by definition not merely a prior cause but a medium (Lat.), that is, a means, for communicating the causality of the first efficient cause. From this it also follows that if there were no first cause, any discussion of intermediate or middle causes would be pointless. Without a first there is no intermediate cause, for the first cause is alone the cause of the intermediate's causing.

Clarification. St. Thomas's own words are the clearest reply to the repeated objection against the first two ways that if the world were eternal an infinite regress would be possible. "In efficient causes it is impossible to proceed in infinity per se. Thus, there cannot be an infinite number of causes that are per se required for a certain effect, for instance, that a stone be moved by a stick, the stick by the hand, and so on to infinity. But it is not impossible to proceed to infinity accidentally as regards efficient causes. For instance, if all the causes thus infinitely multiplied should have the order of only one cause, their multiplication being accidental, as an artificer acts by means of many hammers accidentally, because one after the other may be broken. It is accidental, therefore, that one particular hammer acts after the action of another. Likewise it is accidental to this particular man as generator to be generated by another man; for he generates as a man, and not as the son of another man. For all men generating hold one grade of efficient causes, namely, the grade of a particular generator. Hence, it is not impossible for a man to be generated by man to infinity. Yet such a thing would be impossible if the generation of this man depended upon this man, and on an elementary body, and on the sun, and so on to infinity" (Summa theologiae 1a, 46.2 ad 7).

In this way, as in the first, only the existence of the first efficient cause is established by the proof. No implication as to the nature of the first cause is mentioned, although philosophically a number of notions are derivable from the demonstration. Clearly, God is an uncaused efficient cause; otherwise the same contradiction would be involved in Him as in any cause that is a cause to itself. Pushed further, this proof as well as the others is meant to establish that God is the total cause of all being, even though secondary causes genuinely exercise causality. The secondary causes are only partial; the activity of God as first efficient cause is constant. Hence the concept of God as "winding up" the universe (as though it were a toy top) and letting it go to unwind is erroneous; for the proof from efficient causality makes it clearly evident that intermediate causes really depend on the first cause here and now. The first efficient causality's act always has an influx into whatever is or operates, since the dependence of the secondary causes on the first efficient cause never ceases. (see causality; efficient causality.)

Proof from Contingency

Of the five ways, the third is the least popular and probably the most controvertedboth by reason of the argument proffered and because of textual difficulties. Nevertheless, eventually modern scientists may well find this proof closest to their own kind of thought. The demonstration is based on being rather than on operation and has at least a remote affinity to notions of probabilities.

Argument. The third way begins from the observable fact that some things have a contingency surrounding their existence. Contingent in the present context is understood as meaning possible to exist and not to exist. An obvious illustration of contingent existence is the constant generation and corruption of plant life. If all things have this intrinsic potency to be and not to be, then, carrying the supposition to its ultimate limits, at some moment in the past nothing at all existed. This validly follows because whatever has an intrinsic existential contingency has a limited duration, a beginning and an end.

St. Thomas has deliberately placed a false hypothesis: "If all things (that exist) are possible to exist and not to exist, at some time nothing existed in reality." The assumption that nothing existed at one time leads to the absurdity that nothing exists now; for nothing can come to be except through something already existing, and this has by supposition been ruled out. Only after squarely facing reality does St. Thomas deny universal contingency and draw the obvious inference that some necessity is demanded in things.

Difficulties. Conveniently, at this phase of the demonstration a number of difficulties can be mentioned. First of all, some have objected that the doctrine of creation is a necessary element for the cogency of the proof. On the contrary, introducing creation would mean penetrating into the nature of God when only His existence is at issue; further, the doctrine of creation is not required for the force of the proof, since the next step of the demonstration leads to the cause behind contingency. Secondly, St. Thomas cannot be accused of arguing gratuitously that all things are contingent or even that contingent things cease to be through annihilation. The argument looks to the past and not to the future in its first premise; its forward motion comes as the reasoning seeks out the necessary element in reality. Finally, the objection that St. Thomas is guilty of the error he himself noted as a weakness in the ontological argument, that is, that he argues from the possible order and concludes at the level of reality, is not justified; for the hypothesis is presented as false.

Contingent beings, then, are not sufficient to explain the existence of reality. Also, an infinite regress among contingent things of this kind is impossible. This would demand a series of infinite duration composed of things having only a finite duration; such a concept is absurd. Appeal must therefore be had to necessity in things. Things are said to be necessary if they cannot not be, that is, there is not present in them a potency not to be.

Necessary Being. Many philosophers unable to discover any evidence of necessity in things protest that the proof is therefore invalid. Necessity in propositions they concede, but not necessity in existence. Nor can their objection be refuted by recourse to necessity in operations, as breathing is necessary for life. The third way rests on necessity in being, not in operation. One accepting the hylomorphic theory might point to primary matter, not as necessary in being, but as the necessary underlying principle of change. One can offer the human soul as an illustration of a being that has a necessary existence by reason of its simplicity in essence.

However, the validity of the demonstration does not demand an unequivocal answer to the question of the existence of some necessary being in the universe of immediate experience. The proof has led to the conclusion that necessity is demanded in things because contingency is inadequate for the work of sustaining dependent beings. Once this is established, then the next step is that whatever is necessary is so either from another or not. As in efficient causality, likewise here, nothing can be the cause of its own necessity, and an infinite regress is impossible. This means that a being must be posited that is intrinsically necessary, with no dependence from outside to account for its own necessity in existence. Indeed, this being is the cause of necessity in others; it is the being men call God.

The argument treats mainly of necessity in regard to existence as such. Whether some observable things always existed or not does not affect the course of the reasoning. If planets were eternal, that is, have had an infinite duration in existence, the problem of what caused their existence and permitted this endless duration would still remain. On the other hand, if all things really are contingent in their existence then a necessary being is still needed to explain how they came into existence at all and continue to be.

Textual Variants. As mentioned above, the proof has various readings. The Leonine (1880 edition) has: Impossibile est autem omnia quae sunt talia, semper esse: quia quod possibile est non esse, quandoque non est. "It is impossible, however, for all things which are such (possibles), always to be: because what is possible not to be, sometimes is not." All the other codices, dating back to Vaticanus of the 13th century, read: Impossibile est autem omnia quae sunt, talia esse, quia quod possible est non esse quandoque non est. "It is impossible that all things are, be such as these (possibles): because what is possible not to be sometimes is not." This second reading seems the more accurate because it follows the movement of the thought of the demonstration more closely. In practice, commentators using either version come to the same conclusion.

Proof from Grades of Perfection

Man clearly sees that some things are better than others. Much advertising is based on this trutheven the same kind of product, such as soap, will have claimants declaring one brand superior to all others. The point under consideration is a perfection that admits of more and less, not one that is indivisible such as humanity, which one either has or does not have. Further, in the realm of transcendental perfections involving analogical conceptssuch as good, true, and nobledegrees of perfection are even more pronounced.

Argument. The fourth way is clearly in the setting of these transcendentals, which are perfections without any intrinsic limitation in themselves and yet are found in diverse things in different degrees or modes. These perfections of good, true, and noble as found in sensible reality do not flow from the nature of the things themselves. Whatever flows from the nature of a being cannot be had according to more or less; thus all men by nature have the perfection of humanity absolutely, whereas beings that are not men do not have this perfection at all. If the things of experience possessed the transcendental perfections in the way that man possesses humanity, they would have these perfections in a full, absolute way; in other words, one should expect the things he encounters to be good, true, and noble without limitation. Since this is evidently not the casesince the things of this world have goodness, truth, and nobility in varying degreesone must conclude that these things do not possess the transcendental perfections by their nature. And, therefore, they must receive these perfections from outside, from some absolutely perfect cause that is not merely exemplary but also efficient.

The conclusion that the being of supreme perfection must be the efficient cause of perfection in all others is reached with the help of an Aristotelian principle: Whatever is the greatest in any kind (genus) of being is the cause of all that are of this kind (genus). Since this principle is somewhat subtle, St. Thomas introduces a vivid illustration. Fire is hot by its very nature, while other things, such as water and metal, become hot by participating in the heat of the fire, more or less intensely so by reason of their proximity to the fire. This participated perfection can be retained only so long as the being in which the perfection properly exists is efficiently causing the perfection in others; as soon as the fire is withdrawn, the water begins to cool. Likewise, the being in which all transcendental perfections are realized absolutely must be the efficient cause of whatever participation of these perfections is found in other things. And this supreme source of all perfection is the being men call God.

Use of Plato and Aristotle. Although the reference to efficient causality and the example of the fire are based on aristotle, a Platonic notion is really at the heart of this fourth way. In the Summa St. Thomas does not mention plato, but in another work (De pot. 3.5) he acknowledges his indebtedness to the author of the Dialogues. St. Thomas actually invokes an analogy of proper proportionality, and Plato's doctrine supplies him with the basic insight.

Plato's own words should make evident what St. Thomas took from him. "He who has been instructed thus far in the things of love, and who has learned to see the beautiful in due order and succession, when he comes toward the end will suddenly perceive a nature of wondrous beauty a nature which in the first place is everlasting, not growing and decaying, or waxing and waning; secondly, not fair in one point of view and foul in another but beauty absolute, separate, simple, and everlasting, which without diminution and without increase, or any change, is imparted to the ever growing and perishing beauties of all other things" (Symp. 211). As with beauty, so too with good, true, noble, a supreme or greatest must exist.

Plato carried his theory to what is known as the world of Forms and Ideas, some kind of separate world where genuine archetypes apparently existed as distinguished from the "shadows" of them in this material world. Whatever Plato really meant is not at issue in this proof. St. Thomas does not accept any extreme presentation of the Platonic theory. What he does see in it are the elements basic to the analogy of proper proportionality and the truth made evident through this analogy, namely, that there is some one First to which all others are referred and from which they derive their share of truth, goodness, beauty, etc.

Having discovered, or perhaps inserted, analogy in Plato's doctrine, St. Thomas turns to Aristotle in order to show that what is supremely true and good must be supremely being. In the text explicitly cited at this point (Meta. 993a 30-b 30), Aristotle's context is different from that of St. Thomas. Aristotle is discussing the arduous effort involved in investigating truth and concludes with the observation that "the principles of eternal things must be always most true so that as each thing is in respect of being, so is it in respect of truth." St. Thomas borrows this thought in order to arrive at God, who is First Truth and First Being. Finally, as has already been noted, it is to Aristotle that St. Thomas appeals in order to establish that the God who is First Truth and First Being is the efficient source of the truth and the very existence of all other things.

Proof from Order

Another evident fact of experience is the orderly operation of nature. In the overwhelming majority of cases, the earth brings forth her fruits and is thoroughly predictable as to her activities. Although lacking knowledge, the acorn is moved almost without exception toward its proper end of becoming an oak. Such uniform and consistent attainment of goals by nescient beings requires an explanation. To attribute it all to chance would be hopelessly naive, since chance by its own connotation means something out of the ordinary, something not within the normal order of procedure. A more profound explanation must be sought.

Argument. The fifth way is carefully restricted to natural things lacking knowledge. Hence the proposition that a watch requires a watchmaker to design and make it is really not pertinent to the present demonstration, nor indeed is it the most helpful illustration with which to suggest the existence of God. For one thing, unlike nature, the watch continues to exist independently of the watchmaker once he has made it. Likewise the present proof is based rather on the notion of the government or guidance of natural things, rather than on design as such.

St. Thomas's example, chosen with his customary precision, is that of an arrow moving toward a target. The arrow is directed toward its end; so is nature. The arrow depends entirely on the archer for its operation; nature depends entirely on something outside herself. Lack of knowledge is a definite limitation in a being acting for an end; the lack must be supplied in some way from without by a knowing being.

Thus the orderly movement of natural things toward their proper ends indicates the presence of an intelligent being. Order demands intelligence, because order is the arrangement of things in a definite series according to a norm, and only an intellect can conceive the relationships involved in such arrangement. The establishment of means to an end requires some foresight, some comprehension of relations, and even more primary, a conception of the end itself. Only an intelligent being satisfies these conditions.

A deeper insight into the argument is obtained when it is recalled that good and end are convertible terms. For St. Thomas, the best evidence that natural things act for an end is the fact that they tend to act in such a way as to achieve what is best for them. The conclusion to an intelligent being rests, in the final analysis, on the need for an agent by whose intention the things of nature are directed toward their good. Thus the proof begins by considering natural things as passively governed in their movement and ends with an intelligent agent or efficient cause that actively governs them.

Clarifications. Certainly there are numerous cases in which natural things fail to attain their end, but the failure is due to what may be called accidental interference; thus the acorn will die in the earth if conditions for its survival are not present. At any rate, instances of failure can never outweigh the overwhelming evidence that exists for order and finality. The fact that nature does consistently attain her goals argues to the existence of an intelligent being. Furthermore, the constant achievement of the end means that the intellect responsible for the operations is never idle, but is exercising its causality continuously. And the intelligent ruler who exercises universal and constant direction over nature is the being men call God.

Much confusion over the fifth way is avoided if one remembers that the demonstration is concerned only with internal finality, not with external finality. An acorn is of its own intrinsic nature potentially an oak tree; it has a tendency to attain that end in a favorable environment. Later the tree may be chopped down and made into toothpicks; but that involves another scheme of things not pertinent to the fifth way. Hence the answer to the question whether the purpose or end of the egg is to be a chicken or an egg sandwich is: the intrinsic end of the egg is to be a chicken; the external ends of the egg are as limitless as its possibilities (see final causality).

See Also: god in philosophy, 2; agnosticism.

Bibliography: Thomas Aquinas, Summa theologiae 1a, 2, Eng. tr. and comment. v. 2, ed. t. mcdermott (New York 1964), 60 v.; Suma teologica, 16 v. (Biblioteca de autores cristianos dispersed nos. 29197; 194760) v. 1, q. 126, with notes on the proofs by f. muÑiz. t. c. o'brien, Metaphysics and the Existence of God (Washington 1960). j. maritain, Approaches to God, tr. p. o'reilly (New York 1954). r. garrigou-lagrange, God: His Existence and His Nature, tr. b. rose, 2 v. (St. Louis 193436).

[r. c. smith]