Appeared in Fall 1993, Vol. XIX, No. 2,3

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The question of the demonstration of the existence of God has occupied the thoughts and arguments of many Thomists. All agree that the existence of God can be demonstrated in philosophy. The disagreement turns around the origin of the demonstration. This involves a further argument about the origin of the common understanding of the term “God.” St. Thomas clearly states that God’s existence must be demonstrated from his effects.1The name of God cannot be defined because His essence and existence are one. As the created intellect cannot comprehend his existence, so it cannot comprehend his essence so as to define it. Since God’s essence cannot be comprehended by a created intellect, he cannot be reduced to a genus. As he cannot be reduced to a genus, he cannot be defined. So to be an object of demonstration or question, there must be some other explanation of the name or term given to God by men than one which would be capable of definition. The signification of the name God and its origin is here taken as the middle term in a demonstration and the explanation of the name cannot be a definition. It must therefore be derived from the effects of God and be a quia not a propter quid demonstration.

There are many opinions about the origin of this name. For some it is derived from revelation; for others from an examination of the Metaphysics of being without any reference to Natural Philosophy; for others from the act of judgement; for other from the things in themselves which we experience; for others from the desire of intellectual beings to know God. In this paper, I want to examine the exact manner in which men become aware of God and then how this could be an object of question in a science. There are some who think that the question of the origin of the name for God must be radically distinguished from the question of his existence. While it is true that the problems are not exactly the same, they do overlap. When Aristotle calls God the First Cause and the Unmoved Mover, does he mean a being which cannot be reduced to a genus for definition or a being in whom essence and existence are one, even though he may not exactly use these terms.

I shall now list the various positions usually invoked as authentic interpretations of St. Thomas. Each has much value to it. In this little article, I have given a few minor problems with these positions to show that there is need for further clarification. I in no sense mean these problems to be an exhaustive criticism of the positions involved. The explanation I hope to give in the body of this article should explain the various problems with each position in a clearer light.


A. The Meaning of the Notion of God
must come from Revelation

This is the position of the Gilson school. The main effect of God is esse as manifested in the name God gives to himself on Sinai, ego sum qui sum.2But to demonstrate this requires an appreciation of the real distinction between essence and existence, which involves a correction of certain ideas of Aristotle.

Such a knowledge can only come from the notion of God found in revelation and specifically from the ego sum qui sum (Yahweh). As a result, though God’s existence can be demonstrated by reason, it can only be demonstrated by those philosophers who are aware of the authentic notion of God which is contained in the Holy Scriptures. These are the Christian philosophers and those who know about Judaeo-Christian revelation. Plato and Aristotle did not come to the notion of being as being. They only examined particular being and so they could not have a fully developed Metaphysics. Since the demonstration of God in Metaphysics demands a concept of being as being, which includes immaterial being, they could not know about him.3

One small problem with this position is that it is based on the assumption that the only authentic name of God is one from revelation like ego sum qui sum. This is because it is the one which most properly expresses the notion of subsistent esse. St. Thomas says many times that the names which philosophers give to God are from his effects and these effects are the sensible effects. In fact, the names in the Bible are even derived from things which are known to us by the senses.4



While one cannot deny that God’s self-revelation on Sinai is the most proper name for God, this does not mean that the knowledge of subsistent being is only limited to those who have heard this name. Nor does it mean that other names for God do not in fact truly express something about his being, for example, uncaused cause or subsistent being itself.

B. The Meaning of the Notion of God comes
from Esse in Metaphysics

This position has many proponents who disagree among themselves as to the origin of the notion God within Metaphysics. I have chosen two excellent representatives, Joseph Owens and Thomas C. O’Brien.

Joseph Owens5 holds that the notion of God is found in the concept of esse gained from the act of esse discovered by the intellect. The examination of it is a posterioriand depends on some concept of material being. Once one material being is experienced, from the rich experience of the existential act found in the judgement about it, one ascends to the discovery of common being and the causes of common being, which include God.

As a result, the mind can understand the existence of God from examining the causality of the existential act found in the union of the mind with the thing in the judgement, the second act of the intellect. One does not need to investigate Natural Philosophy in discovering God or Metaphysics by means of causality.

Thomas C. O’Brien’s6 position seems similar to this one. For him though, the real distinction between esse and essence is only known once one has arrived at the existence of God. The existence of God may be discovered in Metaphysics a posteriori, but from examining act and potency. Still, the consideration of Natural Philosophy does not seem to be necessary.7

This position does not seem to do justice to several common teachings of St. Thomas. St. Thomas often affirms that according to the order of the sciences, Physics must be known before Metaphysics. In Physics, one comes to know about the existence of beings which are not material. Otherwise, Physics would be first philosophy. St. Thomas is clear that this is the way man historically discovered the true science of first causes, Metaphysics. Another problem is the very character of human knowledge which ascends little by little to the ultimate causes of the world. If it were so easy to discover the first cause, one wonders why it took philosophers so long to do this and why this long discourse is not better understood by more people.

C. The Notion of God comes
from His Causality in Mobile Being

This opinion is well-represented by Fr. William Wallace and Fr. James A. Weisheipl and does justice to the texts of St. Thomas.In my opinion, this is the correct position, but sometimes the way of presenting it has done a little violence to the thought of St. Thomas. Many thinkers have the idea that the purpose of Natural Philosophy is to discover the existence of God and that God is a proper object of the science of nature. Further, following the philosophers of the Enlightenment, they have the idea that one must first prove the existence of God by reason in order to have a Metaphysics, or prove it in theology by reason in order to have a science of faith. As a result, I think the character of the discovery of God in natural philosophy must be made more explicit.

According to this opinion, God is reached in natural philosophy as the cause of changeable being. After demonstrating the necessity of immaterial beings, both angels and God, one can know the possibility of another science, Metaphysics. At the end of his examination of changeable being, the philosopher concludes to the necessity of immaterial being, the Unmoved Mover. The Unmoved Mover does not properly belong to Natural Philosophy. This allows the philosopher to proceed to a science concerning being in common where God and his attributes are properly discussed and distinguished according to his names.8 God is not the object or the subject matter of Metaphysics, but one must reach the necessary conclusion of his existence at the end of the science of mobile being in order to explain limited mobile being.

This opinion has many advantages because it does justice to the texts of St. Thomas about the order in which the sciences are studied and about the Prime Mover being in some way identified with subsistent esse.9It also does justice to the classic idea of Aristotelian logic that no science proves the existence of its own subject matter. If the subject matter of Metaphysics must include immaterial beings, then one can only clarify the subject matter of Metaphysics after proving the existence of other entities besides material beings, such as the human soul and the first Unmoved Mover. Once these entities have been proved, then the mind can make a further separation in being to include beings which are not material and therefore being as being must include immaterial beings in its consideration.

The first beings men experience are the sensible ones and their discovery of other ones is always in light of these.’o According to the natural way of human knowledge by abstraction, a deep and sensitive experience of mobile being is necessary for the mind to ascend to the separation which is immaterial, immobile being. St. Thomas concludes the Physics by referring to the Prime Mover, who is not the subject of motion, but whose existence is necessary to explain beings which are subject to motion perfectly.10

D. The Notion of God is derived from the Natural Desire to see Him and is an a priori Transcendental

This is the opinion of Joseph Marechal and is one of the basic theses of Transcendental Thomism. According to this opinion, the demonstration of the existence of God is a priori because it is a necessary conclusion of the natural desire in man to see God. All knowledge comes first from certain a priori principles a la Kant. This dynamism is expressed in the natural volition of good and the necessary possibility of fulfillment of good. It is the intuition of this a prioricondition and the remote possibility of fulfillment which is the basis for the demonstration of the necessity of absolute being.12The proof of this absolute being generates the objective character of knowledge.

There are some evident preliminary problems with this position. St. Thomas says that knowledge begins in the senses and conclusions concerning immaterial things are a posteriori in philosophy.Even the notions of God found in Theology are derived from sensible things. Moreover, the natural desire does not refer to the beginning of knowledge, a transcendental a priori condition for knowing truth, but to the potency of intellect to its last perfection. To claim that one must have the last perfection in execution before he can have the first imperfection in execution seems rather strange. The vision of God is the ultimate perfection of the intellect in second act. It does not take the place of the first principles of knowledge. To know about the quia of God, is not a necessary precondition to reduce the intellect to act in knowing about the truth of material things, e.g. form and matter, act and potency, being and becoming, generation and corruption, etc. The quia of God is a conclusion from these truths, not their cause for us. One could say that this position makes the knowledge of the existence of God the efficient cause of all knowledge, not the final cause. This is in direct opposition to clear texts of St. Thomas. In theology, the order may be different, because it begins with what is most knowable in itself, not what is most knowable from our point of view.

E. The Notion of God’s Existence depends on Revealed
Theology and is Necessary as a Precondition
for studying Metaphysics

This last opinion is the classic position of the twentieth century manualists and seems to be inspired by Christian Wolff.13Although these manualists are not specifically concerned with the problem of God in Natural Philosophy, they have developed a very influential school about the place of the quinque viae in philosophy which has important implications for this problem. FollowingWolff, they divide Metaphysics into twoparts: Ontology and Special Metaphysics. To establish the possibility of ontology, one must establish the cause of common being. So God’s existence must be proved first in Metaphysics using the proofs from Theology before the philosopher can go on to investigate further about being and the attributes of God. All else follows from these proofs. The proofs are Metaphysical but a priori in philosophy and preconditions for studying the science of Metaphysics.

The critique of this position turns around the failure of these philosophers to distinguish God as a subject of Theology and his place in the subject matter of Philosophy. It has been justly pointed out that God is not properly the subject of Metaphysics.He is a subject only in relation to the subject matter of common being as its cause. Those who posit this opinion have some difficulty in separating Theology which is revealed from Natural Theology. They also have some difficulty explaining just why it is necessary to study Natural Philosophy at all, though the texts of St. Thomas are clear about this as to the natural order of investigation in the sciences.

F. Towards a Solution to the Difficulty

All of these opinions have merit in contributing to a solution to the problem of the origin and nature of the demonstration of the existence of God in philosophy. I would like to contribute some nuances which will point out the difficulties in some or expand on positive points in others.

First, all the names of God in St. Thomas are essentially related to the notion of God gained from sensible effects. These names are not definitions because our minds cannot comprehend either the essence or the existence of God. Rather, what men call God, or the commonly accepted meaning of the name is used in place of a definition. This is because the demonstration is from effect to cause, the only proper procedure from our point of view. The effect takes the place of the definition of the cause in the demonstration.14If God is demonstrated in philosophy, as St. Thomas is sure he is,15then the meaning of the name of God must arise from some source other than revelation to be the middle term in a truly philosophical demonstration. The concept cannot come from faith alone or only from Holy Scripture, but must come from the effects of God,16 in this case the sensible effects because even the names which faith uses arise from the experience of the sensible beings,17although their source is from God’s revealing them, not from the process of abstraction.

The question then arises as to how one can place the question about the existence of God in philosophy according to the methodology of philosophy to proceed to a demonstration. Not everything can be an object of question, but only things which are known to exist through arguments or discursively.18The problem is that one cannot make something an object of question the existence of which no man knows by science.

The existence of God is reached through reasoning about those beings which are connatural to our way of knowing as we do not have an experience of the self-evidence of God, even though God is the most knowable being in Himself. We must come to identify our word, God, with a being we know about from examining those things open to us. Yet we cannot posit a question about this being according to the method of philosophy without discovering his existence. Since this being is not a material being, no philosophical science can begin by asking whether God exists. We must begin with the material beings we know and by searching through the beings we know discover their first cause. We do discover such a being, but without looking for him.

In other words, the existence of God comes to be affirmed at the same time as one discovers fully the nature of the beings we know, which are composed, contingent and material. It is not reached discursively first as an object of question in any natural science. Nor is it reached exactly inductively.19 God is reached accidentally at the end of Philosophy of Nature. One arrives at the necessity of the immaterial being without making Him an object of question. One comes to know the being one identifies with the first cause of the world concomitantly with discovering the nature of changeable being, when one becomes aware the changeable beings must be effects.

This does not mean that the existence of God belongs properly to Natural Philosophy. What one searches for in Natural Philosophy as an object of question is the knowledge of the things naturally experienced by us as connatural to our way of knowing, the sensible, material beings. This is the proper beginning of knowledge quoad nos. When the first philosophers began to investigate being, they began with sensible beings, the only one known by them. They assumed these beings were identical with being as being and since they wanted to explain the first cause of all being they posited the fact that the first, universal cause of universal being was material. But the sensible, changeable beings could only be perfectly known by knowing that they depended on another being to be. The first philosophers, who approached the subject of being as being did so in a natural way. They tried to flee ignorance about material things by discovering the first cause of all. The first philosophers, who little by little fled ignorance about material beings, thought Natural Philosophy was the science of being as being, because they had not yet discovered that there was more to being than material being, something they could only discover because of man’s way of knowing by examining material beings. Once they discovered the existence of this other being, they discovered Metaphysics.20Without discovering this other being, Natural Philosophy would be first philosophy and there would be no Metaphysics.

Before this discovery is made then, man tries to explain first causality in a purely material way, in fact, he uses only secondary causes as the first causes. The first philosophers posited all sorts of things as first causes: fire, earth, air, water, a mixture, a material mind, number, etc. In trying to explain all material effects, they were compelled by the things in themselves (ipsa rei evidens natura) to dream the truth, as though compelled by the truth itself (somniabant quodammodo veritatem).21They Natural Philosophy. The duty to teach others of that existence and investigate its properties, comes in Metaphysics or revealed Theology. When St. Thomas proves the existence of God in the quinque viae, he is doing so as a theologian who assumes the job of a philosopher and teaches the faithful that one can demonstrate the existence of God, a given in revelation, also from reason alone. The concept does not come properly from faith, even though names like ego sum qui sum (Yahweh) are only revealed. The concept or content of the name God comes from sensible effects. It seems unnecessarily difficult to discuss the quinque viae outside the method of theology as a science, even though many or all of the same arguments may be used in philosophy according to a different methodology.

One may also see this necessity because no science proves the existence of its own subject.22 The existence of immaterial beings must be known in Natural Philosophy because otherwise it would be the science of being as being. There could not be a separate science, Metaphysics. The existence of immaterial things is known in this science, but only accidentally.

By their very nature, then, things lead us to discover God, but without looking for him. Man goes out to look for order and meaning in the material, sensible, changeable world like someone goes to a field to dig a grave. In the process of digging the grave, he finds the treasure which is God’s existence, but not just by chance or fortune like other accidental discoveries. The things in themselves have the light to yield this knowledge. He is compelled to discover this truth for a complete explanation of the order of the material things as particular things themselves.

Man, then, dreams the truth compelled by the changeable beings to the being on which these depend, which must be completely different. The dream is the intuition that there must be a first cause of all the effects known by man which man can directly experience before he can explain the existence of the sensible things known by him. The disillusion of the philosopher is in trying to make that cause a material one. Strangely, because of the limitations of the methods of positive science, the explanation of the causes of the world of modern scientists and philosophers is very primitive. What the ancient pre-Socratics posited because of their place at the beginning of the evolution of ideas, the modern philosopher or scientist takes as a solution because of the limitations of his method.

For the ancient philosopher, the evidence of the things in themselves leads him to the immaterial order. They lead him not just to the angels, for they are more like reflections of the prime cause, but to God Himself. Nothing else will do. The discovery of the existence of God does not come to usa priori in faith or from the necessity of the natural desire for God. It is a posteriori, but does not come to us first in Metaphysics, because then the science would prove what was necessary to its own subject matter. Nevertheless the demonstration of God as a teaching device or proposing him as an object of question is proper to the order of that science. There can be no final explanation of the beauty and order of the material things in themselves, without arriving at the first immaterial cause which is done as the crown of Physics. “The fool has said in his heart, `There is no God’.”



1“Sed quia nos non scimus de Deo quid est, non est nobis per se nota sed indiget demonstrari per ea quae sunt magis nota quoad nos et minus nota quoad naturam, scilicet per effectus.” Aquinas, Summa Theologiae, I, 2, 1, ad corp.; “Unde Deum esse, secundum quod non est per se notum quoad nos, demonstrabile est per effectus nobis notus,” ST, I, 2, 2, ad corp.; ST, I, 2, 2, ad 2; ST, I, 2, 2, ad 3; Summa Contra Gentiles, I, 12 (n. 77); De Potentia, q. 7, a. 3.  

2Cf.E. Gilson, L’Esprit de la Plailosophie Medievale, v. 1, Paris, 1932 (Gifford Lectures), pp. 240-242. For example, “It is necessary to admit that the Thomist proofs for the existence of God are developed upon the existential plane. ..” Cf. ibid., p. 76 (New York: Scribner’s, 1940).

3“..but that this Greek contingency in the order of intelligibility and becoming ever touched the depths of the Christian contingency in the order of existence – that is something of which we have no sign at all and nobody could even conceive it without having first conceived the Christian God … What Plato and Aristotle both lacked was the ego sum qui sum.” Etienne Gilson, The Spirit of Medieval Philosophy (NewYork: Scribner’s), p. 71. Also in Note 4 on page 438, Gilson speaks of the famous text in St. Thomas Aquinas, In Phys., lib. VIII, lect. 2, n. 5, saying, “The interpretation of this and similar texts in St. Thomas cannot be dealt with in a lecture … Surprise is sometimes expressed that St. Thomas should attribute the idea of creation to Plato and Aristotle. But in fact he did nothing of the sort.” Cf. Aquinas, Summa Theologiae,Editiones Paulinae, Rome, 1962, p. 219, note 15; “Sequentes veropervenerunt ad cognitionem revelationem substantialem; postea vero, Plato et Aristoteles, pervenerunt ad cognoscendum principia totius esse,” in VIII Phys., II.

4“Nam omnia divina nomina imponuntur vel ex remotione effectuum ab ipso, vel ex aliqua habitudine Dei ad suos effectus,” Summa Contra Gentiles, I, 12 (n. 79); “Cognitio fidei autem habet a sensu, inquantum significationes nominum, quae proponuntur sensibus, cognovit,” in III Sent. d. 24, q. 2, qla. 3, ad 3.

5“. .. that, as St. Thomas’ lengthier treatment of the Aristotelian argument shows was the viewpoint of existence.” Joseph Owens, St. Thomas Aquinas on the Existence of God, ed. John R. Catan (Albany: State of New York Press, 1980), p. 188 among many other places.

6“Rather, Metaphysics reaches God by its inquiry concerning its proper subject.” Thomas C. O’Brien, O.P., Metaphysics and the Existence of God (Washington, DC: The Thomist Press, 1960), pp. 262-263.

7Cf. for example, In Comm. Liber de Causis, Proem. (n. 7), where the order of learning is: Logic, Mathematics, Natural Philosophy, Moral Philosophy, and Divine Science.

8Cf. William Wallace, The Elements of Philosophy (New York: Alba House, 1977).

9Aquinas, De Potentia, q. 3, a. 5, tertia ratio; Compendium Theologiae, cc. 3, 6, 11.

10Cf. In I Meta., lect. 6 (n. 78); In III Meta., lect. 6 (n. 398); In XII Meta., lect. 6 (nn. 2517-8); In VII Meta., lect. 17 (1671). “In Boeth. de Trinitate, q. 5, a. 2, ad 3.

11In Boeth. de Trinitate, q. 5, a. 2, ad 3.

12“On the other hand, if the first causes of the motion are, at least in part, free agents, they may create, in the subject who is in motion, an initial orientation whose full development remains subordinated to a new free intervention coming from them. In this event, it is not certain that the subject in motion, whatever may be its natural “desire,” will beable to reach its ultimate end. Reaching this absolutely ultimate end would belong only to the domain of remote possibilities. The only thing which would be certain is the existence of all the factors required for that possibility.

Our “natural desire” for the vision of God belongs to this second category …

With St. Thomas we shall conclude that the natural impulsion of our intellectual faculties drives them towards the immediate intuition of the absolute Being. It is true that this intuition exceeds the power and the exigencies of every finite intelligence, left to its sole natural resources. Yet the radical impulsion which drives it to this intuition is not conceiv­able without the objective, at least remote possibility of reaching it.

But this objective, even remote, possibility implies two necessary conditions: the existence of an absolute being, which is capable of communicating itself, and the capability of our intelligence for receiving this communication.

But, if this is the case, if the “vision of the divine essence” is not a utopian perspective, but something which is “possible in itself,” we know now to what “absolutely last end” our intellectual representations refer during the dynamic and implicit stage of objective knowledge.” Joseph Marechal, Le Point de Depart de la Metaphysique, Cahier V, ed. and trans. Joseph Donceel, S.J. (New York: Herder and Herder, 1970), pp. 174-75.  

13For an excellent summary of this position see W.A. Wallace, O.P. 4atural Theology.” Article in The New Catholic Encyclopedia (New York: McGraw Hill Book Company, 1967), v. 14, p. 63.

14“Quia ad probandum aliquid esse, necesse est accipere pro medio quid significat nomen, non autem quod quid est, quia quaestio quid est, sequitur ad quaestionen an est,” ST, I, 2, 2, ad 2.

15“Tum ex philosophorum studio, qui Deum esse demonstrare conati sunt,” SCG, I, 12 (n. 77); “Respondeo dicendum quod post peccatum primi parentis, nemo potuit salvari a reatu culpae originalis, nisi per fidem mediatoris; sed ista diversificata est quantum ad modum credendi secundum diversitatem temporum et statuum. Nos quibus est tantum beneficium exhibitum, magis tenemur credere, quam illi qui fuerunt ante adventum Christi: tunc etiam aliqui explicite, sicut

16“Nomina autem Dei imponuntur ab effectibus,” ST, I, 2, 2, ad 2.

17Cf. note 5.

18“Aequalis est numerus quaestionum et eorum scientia. Cuius ratio est, quia scientia est cognitio per demonstrationem acquisita. Eorum autem oportet per demonstationem cognitionis acquirere, quae fuerint ignoramus.”In Post. Anal., lect. 1(n. 408).

19“Heath in Mathematics on Aristotle, 37-9, makes an ingenious suggestion. He suggests a construction such that it is only following aproof that a learner realizes that what he is dealing with is a triangle …`at the very moment’ one is led to the conclusion, `and that thing is’ is the main use underlying the technical sense of epigoge=induction. Yet the process referred to here is not inductive. The fact referred to is the fact that one already knows a major premiss of the form All M is P; knowledge of the minor premiss S is M may come simultaneously with the drawing to the conclusion S is P…. while it is (for instance) through the middle term `triangle’ that an individual figure is known to have its angles equal to two right angles, it is not through a middle term that the individual figure is known to be a triangle; it is just seen directly to be one.” W. D. Ross, Aristotle Prior and Posterior Araalytics (New York and London: Garland Publishing Inc., 1980), pp. 505-506.

20 In I Meta. lect. b(n. /2i); In III Meta. lect.6 (n. 398), etc.

21... sed et ipsa rei evidens natura dedit viam ad veritatis cognitionem.” In I Meta. lect. 5 (n. 93); “Ipsi antiqui philosophi, quasi ab ipsa veritate coacti, somniabant quodammodo veritatem.” In I de   

22Cf. In I Post. Anal., lect. 1(nn. 13-21); In I Physic., lect. 1(n. 4), “Nulla autem scientia probat suum subiectum.”