Proofs of God's Existence
Proofs of God’s Existence
Thomas’s proofs of God’s existence can serve as a fitting transition point between the principium cognoscendi and the principium essendi, in that they both include, and are motivated by, his notion of being (essendi). Being, he thinks, is understood according to “natural reason,” so it is included in his natural theology (cognoscendi). There is, then, an overlap of Thomas’s principia that we should recognize as we proceed to an assessment of his proofs for God’s existence.
It might seem, at first glance, that the theistic proofs, as developed by Thomas Aquinas, are both too abstract and too antiquated for a post-Kantian world. Aquinas was a man intensely concerned about the science of metaphysics. He dealt, in that science, with abstractions (some would say “speculations”) and methods that would never be allowed in a world subdued by the phenomenal/noumenal distinction of Immanuel Kant.
In spite of this, however, Aquinas’s relevance for contemporary Christian apologetics continues to be defended and asserted. For example, in Both/And: A Balanced Apologetic, Ronald Mayers uses Aquinas’s distinction between “intrinsic being” and “extrinsic being” in an attempt to “balance” presuppositionalism with evidentialism. Mayers proposes a modified or contemporary Thomism as a solution to what he sees as an apologetical impasse.1 Norman Geisler, an avowed Protestant Thomist, borrows extensively from Aquinas’s metaphysics in order to build his apologetical proofs for God’s existence.2 There have also been those within the Reformed tradition who formulate their theistic proofs within a Thomistic context.3
Aquinas’s approach to proving God’s existence is relevant in contemporary philosophy as well. Contemporary anthologies on the philosophy of religion almost always deal with some version of Thomas’s proofs.4
Before attempting to summarize the proofs themselves, some preliminary information might be helpful. Aquinas’s theistic proofs have come down to us as the “quinque viae” or the “five ways.” Although Thomas himself speaks of them in this way, he, as well as his followers, never meant to suggest that these five ways had a set number or order. Aquinas presented his proofs succinctly and most simply in his Summa theologica, but he never again wrote of them as “five ways,” nor did he present them in the same order as in the ST. The ST was meant to be an introductory study, and therefore it does not present the proofs as thoroughly as might be expected in another context.5 In the ST, he seeks to present each of the five proofs in a short and concise paragraph.
In the Summa contra gentiles, however, because it seems to have been written, in part at least, as a manual of apologetics for missionaries,6 the proofs are presented in more detail than in the ST. In the Summa contra gentiles, Aquinas divides the “first way,” which he considers to be the most important, into two arguments, deletes the “third way” of the ST, but includes the other three.7
In De potentia, Aquinas presents the proofs under three heads: one from Plato, one from Aristotle, and one from Avicenna.8 In his Compendium theologiae, Aquinas offers one proof from the argument from motion.9
Thus, while Thomists disagree as to whether Thomas’s proofs are all reducible to one, there is no disagreement about the fact that such proofs were never, in Thomas’s own mind, fixed for the Christian apologist. Thomas used his proofs as the occasion dictated.10
Because Thomas’s proofs are so flexible, both in presentation and in number, it would seem that there should be some unifying principle lying behind them that would help us see their coherence and perhaps even their validity. We will look more closely at that below.
Since Aquinas set forth his proofs in different ways at different times, we will consider them here as given to us in his ST.11
The “first way” of Aquinas, called by him “the clearest proof,” is the argument from motion or change:12
It is certain, and evident to our senses, that in the world some things are in motion. Now whatever is in motion is put in motion by another, for nothing can be in motion except it is in potentiality to that towards which it is in motion; whereas a thing moves inasmuch as it is in act. For motion is nothing else than the reduction of something from potentiality to actuality. But nothing can be reduced from potentiality to actuality, except by something in a state of actuality.13
Aquinas is here borrowing heavily from Aristotle.14 He takes the potentiality-actuality schema of Aristotle from the physical realm and applies it to the metaphysical realm, the realm of being. Aristotle’s primary concern in his argument from motion is not the existence of that which is moved or moving, but the change that takes place accordingly. Thus, the argument borrowed by Aquinas from Aristotle is in the latter’s Physics, not his Metaphysics. Aquinas, however, seems to be arguing from the perspective of being itself, and only in doing so is he able to conclude with the assertion that there is an Unmoved Mover.
Thus, for Aquinas, the potency-act schema is translated into a metaphysical context and utilized as a proof for God’s existence. Aristotle, on the other hand, took existence for granted and thus his four classes of cause (formal, material, efficient, and final) are limited to that which brings about change in an already existing being.15
Although Aquinas insisted that we must indeed begin with that which appeals to our senses (i.e., the physical), he was just as insistent that the physical leads us, on the basis of “pure philosophy” and “natural reason,” to the metaphysical. Such an approach was never delineated by Aristotle in that particular way. When Aquinas speaks, therefore, of the potency-limiting-act principle in his proofs, we are to read this principle primarily as metaphysical, not as referring to the physical.
Notice Aquinas’s first premise in this first proof. He begins, as he always does, with sense experience—he has no room for the a priori in his proofs. From the observation of data, Aquinas moves to observed change or motion in that data. He is speaking here of “accidental” change—that is, changes that take place, not in the substance of that which we see, but in all of those qualities that are changeable, such as shape, color, and taste. These changes are apparent to sense experience.
The second premise of this “first way” is not apparent to sense experience and thus must be shown.16 It asserts that whatever is moved is moved by another. In other words, employing the potency-act schema, Aquinas seeks to demonstrate that whatever is changed or moved is not in itself the agent of change, but is changed or moved by that which actually possesses the accidental quality communicated to the patient. “It is therefore impossible,” says Thomas, “that in the same respect and in the same way a thing should be both mover and moved, i.e., that it should move itself.”17 He uses the example of fire which (being hot in act) makes the wood (which is hot in potency) actually hot. Wood does not have the ability to make itself hot. Changes that are communicated to different things must, therefore, be extrinsic to those things.
Aquinas then proceeds to deny an infinite series of movements:
If that by which it is put in motion be itself put in motion, then this also must needs be put in motion by another, and that by another again. But this cannot go on to infinity, because then there would be no first mover, and, consequently, no other mover.18
Gilson sees Aristotle’s direct influence on Aquinas here.19 Aquinas, in this proof, must have been convinced by Aristotle’s arguments and therefore saw no need to elaborate on them. Thus, Aquinas deems it apparent that God is this Unmoved Mover.
Owens, following Gilson’s new interpretation of Thomas, sees Aquinas’s “first way” as a theological (rather than philosophical) argument:
If you ask why the immobile movent to which it concludes is recognized at once as God, the answer is to be found in the Sed Contra of the article. There God is described in the words of Exodus as I am who I am, understood as meaning that his very nature is to exist. To all who know the God of Scripture, then, his identity with the immobile movent reached by the argument from motion is at once apparent.20
We will remember, from our discussion above, that the new interpretation of Thomas sees this text from Exodus as the beginning point of Thomas’s discussion of being.
As McInerny demonstrates, however, this passage in Thomas is in keeping with his “preambles of the faith,” and thus is meant to be understood philosophically, first of all, and not theologically. The quotation from Exodus is in no way meant to impinge on the purely philosophical process in which Aquinas, following Aristotle, engages in this proof. It is not sufficient simply to quote a Bible verse; Thomas should have argued and shown how the content of revelation grounded his arguments. Instead, he bases them on natural reason, which, as we have seen him argue, all people have in the same way.
The “second way” of Aquinas is the way of efficient causality:
In the world of sense 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.21
Aquinas again seems to borrow from Aristotle in this proof, though Aristotle (contra Avicenna and Albertus Magnus) never used this proof as an argument for God’s existence.22 While the first way deals with the being of things that have changed, the second way deals with the cause of substantial being through secondary means.
Those familiar with the radical empiricism of David Hume would, of course, look askance at Aquinas’s causal argument. It does seem clear, however, that Aquinas saw cause and effect as empirically observable in the same way that he contends for the observation, or at least the extrapolation from observation, of being or existence.23
Aquinas is concerned to show that the being of a particular thing is caused by that which has being in itself. Because he is discussing substantial, not accidental, being, the second way is not as obvious to sense experience, according to Aquinas, as is the first.
Aquinas continues his proof by arguing again against the notion of an infinite regress. Therefore, it is necessary to admit a first efficient cause, to which everyone gives the name of God.24 Though the second way tends to apply the same principles as the first, Thomists contend that it is a self-sufficient proof and able to stand on its own.25
The “third way” of Aquinas argues from necessary and possible existence:
We find in nature things that are possible to be and not to be, since they are found to be generated, and to corrupt, and consequently, they are possible to be and not to be. But it is impossible for these always to exist, for that which is possible not to be at some time is not. Therefore, if everything is possible not to be, then at one time there could have been nothing in existence. Now if this were true, even now there would be nothing in existence, because that which does not exist only begins to exist by 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.26
It is not difficult to see where Aquinas is going with this argument. He begins again with that which is observed, that is, the contingency of existing beings. Possibility and necessity, for Aquinas, are, at least in the beginning of this proof, abstract terms used to describe the observable fact that some things come into existence and others die.27 The argument turns on the contingency of secondary being, which requires something necessary. Aquinas states at the conclusion of the third way:
Therefore we cannot but postulate 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.28
The point of the argument seems to be that, while we perceive contingency in those things that exist, we also perceive that something necessary is required for the rationale of the contingency that surrounds us. Necessary existence, for Aquinas, seems to be tantamount to “being.”29 That which has its being conferred by another exists, not in and of itself, which is the reason for its contingency, but because of another who conferred such existence. Aquinas puts this in the context of his metaphysical potency-act schema:
Hence the potency to not-being in spiritual creatures and the heavenly bodies is rather in God, who can withdraw his influence, than in the form or the matter of such creatures.30
In keeping with his metaphysical structure, then, Aquinas supposes that for anything to have being, though temporal, there must be one in whom being is intrinsic. It is, therefore, an argument from temporal to eternal existence, rather than from bare possibility to necessity in being.
The “fourth way” of Aquinas has been described by some as the only truly metaphysical argument.31 Aquinas argues from degrees found in things to degrees of being, concluding with the ultimate cause of being, which we call God. Things are said to be more and less because they approximate in different degrees to that which is greatest:
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. . . . 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. 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.32
This argument appears to be taken both from Aristotle and from Plato.33 It has been subjected to much scrutiny and to various interpretations. Some have had concerns that Aquinas has bowed the knee to a priorism in this proof and has significantly strayed from the moderate realism that seems to characterize his other proofs.34
It seems more appropriate, however, to interpret Aquinas here in the light of the other four proofs unless there is obvious reason to do otherwise. Thus, we see Aquinas, in this proof, reasoning from the relative to the absolute, beginning a posteriori, that is, with those sensible things that possess certain characteristics in a relative way. Given the existence of those attributes, there must be an absolute that alone would be able to confer such characteristics.
Because Aquinas is constructing a metaphysical argument, as is clear from his citation of Aristotle’s Metaphysics in this proof, he proceeds from the visible to the notion of being. This argument may more strongly point to Aquinas’s principle of participation, individuation, existential metaphysic, and the like, but it does carry through the same basic principles of the other proofs, especially that the created world points to its Creator. We suggest, then, that the proof itself is in accordance with the principles of the others, though perhaps more implicitly metaphysical in character.
The “fifth way” of Aquinas is the argument from providence, or, as he puts it, from “the governance of things”:
The fifth way is taken from the governance of the world. We see that things which lack intelligence, 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 not fortuitously, but designedly, do they achieve their end. Now whatever lacks intelligence cannot move towards an end, unless it be directed by some being endowed with knowledge and intelligence; as the arrow is shot to its mark by the archer. Therefore some intelligent being exists by whom all natural things are directed to their end; and this being we call God.35
This proof is often subsumed under the rubric of the “teleological” argument, and in some sense it is. Yet Owens correctly argues that it is primarily metaphysical, not teleological.36 Aquinas is arguing in this proof, not merely that there is design, but that the things of this natural realm are being moved to a meaningful end by an Intelligence. It is, in effect, at least to some extent, an addendum to the second way.
Aquinas is concerned to prove, not a Designer, but an Ultimate Efficient Cause, who is intelligently moving those things that are without intelligence toward a meaningful end. Thus, Aquinas is operating in a far different realm than, for example, William Paley, whose teleological argument became the standard.37 Again, it is metaphysics that provides the foundation for Aquinas’s proofs, not simply observation or experience.
With that in mind, we need to look briefly at the metaphysical system that informs Thomas’s proofs, as we transition to the next section on “Who God Is.” As with everything we have said thus far, we cannot do full justice to the complexity and depth of Thomas’s metaphysical system here. We can, however, provide a useful focus of that system in order better to evaluate its weaknesses.
In his discussion of archetypal and ectypal knowledge in Reformed thought, Richard Muller notes,
The basic question to be answered . . . concerns the nature of the relationship between the divine archetype and the temporal ectype: is the relationship such that we can ascend by analogy from what is known here to a clear vision of God—the analogia entis—or is the relationship such that we cannot conceive for ourselves a perfect theology?38
In this, Muller highlights the metaphysical analogia entis (analogy of being), which is one of the key aspects of Thomas’s proofs. In order to understand Thomas on analogy, it is necessary to note the central tenets of his notion of “being.”
For Aquinas, being is act in distinction from essence that is potential existence or potency. Being, by definition, is pure actuality. Thus, Aquinas sees existence as at the root of the real.39 It is the one attribute or characteristic that is common to all things and thus is, in Aquinas’s system, a transcendental notion. That is, it transcends the limitations and imperfections of every particular thing that exists.
Aquinas’s metaphysics, then, begins with the primacy of existence over essence. It is existence which confers on an essence its “being” or “act of existing.” Aquinas seeks to delineate this, very simply, by asserting that we can know what a thing is without asserting its actual existence.40 Because we can conceptualize, for example, a unicorn, without asserting its actual existence, there must be a distinction between a thing’s essence, in this case a unicorn, and its existence. This, it seems, is Aquinas’s most basic metaphysical presupposition, which underlies each of his five ways.
Given Aquinas’s distinction between existence and essence, he seeks to show that every thing participates in its “received act of to be” (i.e., “being”) only to the degree that its respective essence permits. This is the Aristotelian potency-limiting-act principle in natural philosophy, translated by Aquinas into the science of metaphysics. In Thomas’s metaphysics, potentiality limits actuality. That is, essence is potential existence. Essence is not in itself existence and therefore does not have existence in itself. When the perfection of being, which is inherently unlimited and transcendental, confers existence on an essence, that which is unlimited and transcendental becomes limited and actual only to the degree that a thing’s essence will permit.
It must be remembered in this discussion that Aquinas always maintained that our knowledge comes to us by way of sensory experience. As we experience reality through our senses, we recognize that certain things both exist and are diverse, which enables us to postulate this metaphysical theory. Being, as inherently unlimited and as the “act of to be,” is limited and actualized through essences.
This combination, according to Aquinas, can be neither a synthetic nor a part/whole relationship. Such is the case because both synthetic and part/whole relationships require that there be three things: the act of existing, the essence of that which exists, and the thing itself. A combination of this sort would require something above and beyond each part, as well as the whole, that is more actual, more perfect.
Yet Aquinas has already asserted that being is the most perfect of all perfections and is in itself actuality. There can be nothing that is more existent than being or more perfect than being. Any synthetic or part/whole relationship would require as much. For Aquinas, the relationship between being and essence could be called a transcendental relation due to the fact that it must transcend every lesser relationship.41
This metaphysical construct gives us the backdrop for Aquinas’s view of analogy, which, again, relates directly to his theistic proofs. It is difficult to find a consensus among Thomistic scholars as to Aquinas’s own teaching on analogy. Such is the case, in part, because this crucial doctrine was never set out by Aquinas in systematic form. There is no “chapter” in Thomas’s writings on analogy.
However, there is widespread agreement that Aquinas did teach what has come to be known as the “analogy of proper proportionality.”42 Analogy of proper proportionality is a metaphysical notion designed to articulate the fact that being itself cannot be seen, but is “perceived” in each thing in proportion to its essence.43 A thing is said to “be” in proportion to its nature. Thus, the being of a man is in some sense similar to the being of a rock and in some sense dissimilar. There is, then, an analogy of proper proportionality between the rock and the man.
As one can see, this analogy is based on the distinction already noted between existence and essence. Phelan maintains that there are only three ways to conceive of any proportional analogy. The first is that the common character or ratio belongs really and truly to each participant in the same way but in unequal degrees. The second is that the ratio belongs really to only one participant but is attributed to others. The third is that the ratio belongs really and truly to each participant, but only in proportion to their being.44 This third analogy, of course, is the analogy of proper proportionality and is the analogy used by Thomas. It must always deal with the relation of existence and essence in a thing and thus is, by definition, proportional.45
In the analogy of proper proportionality, Aquinas seeks to distinguish between the same attributes in different things. He denies univocal predication because of God’s coterminous character.46 That is, because that which is ascribed to creatures or creation is ascribed in a divided and particular way, and because the same ascription would be simple and universal in God (because God is what he thinks and thinks what he is—see the next section), such ascription to both cannot be univocal.
But Aquinas must also deny equivocal predication.47 There is indeed a certain likeness of creation to its Creator, though such likeness can never be predicated univocally. Equivocation would show us that though one name is predicated of several things, we cannot infer from one of those things the knowledge of the other because there is, by definition, no point of reference. We could, therefore, understand nothing of God from creation, which for Aquinas is patently false.
Thus, as Aquinas develops his doctrine of analogy, he argues that that which is predicated of both God and man actually exists in both to the extent that their respective essences permit. To say that “God is good” and that “man is good” is to say that God is good in proportion to his “received act of to be” (which only in God is his essence) and that man is good with respect to his potential existence. Or, to use another example, God knows as God, and man knows as man. The proportion that obtains between being and essence determines the proper predication of that which characterizes each thing.
We begin to see something here of Aquinas’s “scale of being.”48 Every thing is limited in being in accordance with its essence. Every characteristic of a thing is further limited as to the proportion that obtains between its being and its essence. Thus, potential existence limits the received act of to be (existence), and the combination of the two, in a particular thing, limits the attributes and perfections of that which is. We could say then that angels know as angels are, men know as men are, and there is a proportion (1) between knowledge in angels as they exist and (2) between knowledge in angels and knowledge in men. Knowledge, therefore, cannot be predicated in the same way when speaking of an angel’s knowledge and a man’s knowledge, the existences of such being proportional to their respective essences.
But there is a tension within this Thomistic doctrine that has caused some controversy among his interpreters. Simply stated (and on this all seem to agree), the analogy of proper proportionality cannot really apply to God. The reason for this is that the analogy of proper proportionality derives its basis from the proportion that obtains between essence and existence. But in God no such proportion obtains. God is pure act. His essence is his existence. Unlike any other thing, it belongs to the very essence of God to exist. How, then, can a real, proportional analogy be predicated of men, in which every act of existence is limited by essence, and God, in which essence and existence are identical and completely exhaustive of each other? It seems, then, that a second kind of analogy must be introduced that will account for the one in whom essence and existence are identical. Such an analogy has been called the “analogy of intrinsic attribution”49 and can be seen, for example, in the following statement from Aquinas:
Therefore it must be said that these names are said of God and creatures in an analogous sense, that is, according to proportion. Now names are thus used in two ways: either according as many things are proportionate to one, . . . or according as one thing is proportionate to another, thus healthy is said of medicine and animal, since medicine is the cause of health in the animal body. . . . Thus, whatever is said of God and creatures, is said according to the relation of a creature to God as its principle and cause, wherein all perfections of things pre-exist excellently. Now this mode of community of idea is a mean between pure equivocation and simple univocation. For in analogies the idea is not, as it is in univocals, one and the same, yet it is not totally diverse as in equivocals; but a term which is thus used in a multiple sense signifies various proportions to some one thing. . . . Therefore the universal cause of the whole species is not an univocal agent: and the universal cause comes before the particular cause. But this universal agent, whilst it is not univocal, nevertheless is not altogether equivocal, otherwise it could not produce its own likeness, but rather it is to be called an analogical agent, as all univocal predications are reduced to one first non-univocal analogical predication, which is being.50
Note the absence (conceptually, not terminologically) of any proportionality in this statement. Such is the case because Aquinas is now attempting to do justice to analogical predication with respect to the Creator. This analogy of intrinsic attribution, therefore, has as its basis, not the proportionality of things, but their causal relation. The relation of creature to God in the above quote is a causal relation, yet is described as an analogical relationship. Because the definition of potential existence is that which makes a thing what it is, what is of the essence of a thing must be possessed fully by that thing. For example, it is impossible for man to be partly human. It follows, then, for Aquinas, that existence is not intrinsic to created being and therefore must be caused by the one in whom essence and existence are identical. The analogy of intrinsic attribution becomes, then, in one sense, the basis for Thomas’s proofs, as well as for his analogy of proper proportionality.51 As Hart explains,
Analogy of intrinsic attribution, then, will assure us that between limited beings of our direct experience, in whom there is a real relation between essence and existence and a conceivable being in whom there is no such real relation, but identity of essence and existence, there is still real similarity. By our analogy of proper proportionality we can then assert of this latter being, as actually intrinsically possessed, in an unlimited way, all those perfections that we found proportionately in finite beings of our actual experience, with an assurance that only an analogy of attribution can provide.52
Thus, while analogy of extrinsic attribution is foreign to Aquinas’s thinking, because in such the analogon really exists in only one of the analogates of which it is predicated, analogy of intrinsic attribution is affirmed because “being” is caused by, and thus is intrinsic to, all analogates.53 Both analogies, of proper proportionality and of intrinsic attribution, seem necessary to deal with the relationship of God to his world.
Our knowledge of God, then, is always analogical. It depends on the analogy of being (analogia entis), as well as on the causality of God. In this sense, the proofs are all extensions of Thomas’s view of analogy. They presuppose the analogia entis and are rooted in God’s causal activity, as that activity is supposedly demonstrated from the reality of cause and effect in the world. We will see, in the “Critique” below, in the discussion of “Proofs of God’s Existence,” that this is an insufficient structure for such proofs.