Aquinas: God

The Philosophical System of Thomas Aquinas, by Maurice de Wulf, edited and adapted for the web by Jonathan Dolhenty

XI. God

A. Proofs of the existence of God

It has been noticed above that the innumerable individual beings which make up the universe are subject to change, and that the change of anything whatsoever takes place by means of the action of some being other than itself. It is the action of B that causes A to become A. But the action of B itself implies a change in B, and this demands in turn the concurring causality of C, and so on (IX, G). We cannot continue this process back to infinity. For in that case change would be without a sufficient explanation and therefore an illusion, whilst the existence and reality of change is one of the most evident things in nature. The setting in motion of a process of change demands a starting point, an initial impetus, whence the movement proceeds. This absolute beginning is possible only on the condition that a Being exists who is beyond all change, — in whom nothing can ‘become,’ and who is therefore immutable.

This being is God. Now, God cannot set in motion the series of changes constituted by actuality and potentiality except by an impulse which leaves free and undisturbed His own impassability. For, if this initial impulse were to involve a modification, however slight, in the Primary Being, such modification would constitute a change, and require the intervention of a still higher Being. Thus the process would be endless unless God were the ‘prime mover, himself unmoved’ [1].

Let us suppose that one decides to build a house, and that he wants it to have solid supports. To this end he must lay deep the foundations which are to support the building. He must continue to dig until he obtains a base of absolute fixity and security. But obviously he must finally call a halt in this work of excavation, if the building is to be commenced at all. We may therefore, nay must, conclude that the builder did in fact halt at some point in the earth, if de facto the building is there before our eyes.

The same applies to the scholastic argument which we are considering. Change exists as a fact, even as the house in question exists as a fact. Change stares us in the face: it is found everywhere in the universe. But if there were no starting point in the chain of efficient causation, the change itself could not exist. We are not in a position to deny the existence of the evolution of the universe: we must therefore account for it. To suppose an endless regressus in the causal series possible would be like imagining that one can suspend a weight from the end of a chain whose other end simply does not exist, since link is added to link to infinity.

Change is a certain indication of contingency or non-necessity, and this leads Thomas to a second proof of the existence of God, intimately related to the preceding: the existence of non-necessary beings demands the existence of a necessary Being. As soon as a non-necessary being is represented as existing, it ought to be referred to an influence external to itself, and here again a regression to infinity would not explain existing reality. One must stop at an absolutely necessary Being (necessarium absolutum), whose very essence it is to exist, and which finds it own necessity in itself. Such a Being is God [2].

It is important to notice that the notion of contingency or non-necessity, upon which the argument rests, is independent of the notions of time and number. The principle of causality does not involve the concept of time. For, even if the series of contingent beings were without a beginning, these beings could not be made intelligible without the existence of a necessary Being.

It all comes, then, to this: if any given thing is real, the sum total of all those other things, without which the reality of that fact would be inexplicable, must be no less real. From the standpoint of metaphysics, God exists because the existence of the Universe demands Him. Hence the existence of God is not, as one might suppose, a further mystery requiring explanation in addition to the general mystery of the world. The scholastic argument for God’s existence has exactly the same value as the principle of contradiction and of efficient causation.

Such are the principal proofs which Thomas Aquinas brings forward for the existence of God. There are others besides, all of which consist in an interpretation of facts. He sternly rejects the arguments known as ‘ontological’ which would better be described as ‘logical,’ such as those of St. Anselm and St. Augustine. From the content of our idea of God we cannot and may not infer the actual existence of God. The fact that existence is implied in the idea of an all-perfect Being is no guarantee of the real existence of such a Being. To pass thus from the conceptual order to the real order is tantamount to trying to suspend a picture from a painted nail.

B. God is Infinite Being or pure existence

Since material reality is alone proportioned to the knowing powers of man, since the mind only functions with the aid of the body (III, B), God can only be known by us in an indirect way. “The highest knowledge which we can have of God in this life, is to know that He is above all that we can think concerning Him” [3].

In other words, we know God only by analogy, in attributing to Him all perfections — by negation, in excluding from these perfections all elements of imperfection — by transcendence, in removing every limitation which in other beings modifies a perfection. Our knowledge of God consists in knowing that He is infinite. Aristotle stopped at the notion of an unmoved mover. The Schoolmen added to it the notion of Infinity. Let us endeavor to show how this entirely negative concept does nevertheless attain to the Being who is the fullness of reality.

The Infinite Being, says Thomas Aquinas, having in Himself no potentiality, no limitation, is pure existence [4]. In order to realize exactly what this implies, let us avail ourselves of a simile, although in this subtle matter any comparison is necessarily inadequate.

Imagine a series of vessels, with different capacities, which are to be filled with water; let there be tiny vessels, and vessels that will contain gallons, and great receptacles which are to serve as reservoirs. Clearly, the volume of water which may be stored in each vessel must be limited by the capacity of the vessel itself. Once a vessel is filled, not a drop can be added to its contents; were the very ocean itself to flow over it, the contents of the vessel would not increase.

Now existence in a finite being may be likened to the water, in our simile; for existence too is limited by the capacity of every recipient being. This capacity is the sum total of the potentialities which from moment to moment become actual realities by being invested with existence. That oak of the forest which is invested with the most beautiful qualities of its species, and with the most perfect vital forces; that man of genius who is endowed with the most precious gifts of mind and body, — these possess the maximum of existence that can possibly be found in the species of oak and of man. But, be it remembered, the capacity for existence in each of these is limited and circumscribed by the very fact of the apportioned potentiality, or ‘essence.’ In this beautiful conception of Thomas, a vigorous oak has a larger measure of existence than a stunted one; a man of genius possesses existence in a larger sense than a man of inferior mind, — because the great man and the vigorous oak possess a larger measure of powers and activities, and because these powers and activities exist. But, once more, there is a limit even to their existence.

On the other hand, to return to our simile, let us picture to ourselves an existence indefinitely uncircumscribed, say the ocean, without shore to confine or to limit it [5].
Such existence, with no qualifying or modifying adjective, is God. God is existence; he is nothing but the plenitude of existence [6]. All other beings receive only some degree of existence, — the degree increasing in measure with increasing capacity. But they receive, in every case, their existence from God. Finite beings act upon each other, since, as we have seen above, the corporeal world is a network of efficient agents; they determine the capacity of the vessel, and the size varies unceasingly, but it is God alone who gives the existence according to the capacity in question.

C. The Divine Attributes

The study of the Divine attributes amounts to the inquiry by a close effort of reasoning as to what is implied by “Being which is existence without limit.” Thomas enumerates these attributes, and establishes in turn God’s simplicity, goodness, immutability, unity, justice, etc. He is never tired of stressing God’s transcendent individuality, His knowledge and His government of the universe.

His transcendent individuality prevents Him from being confused with any of the limited beings to whom, by a free decree of His will, He has given or will give existence. Any confusion of God with finite beings would be incompatible with His Infinity, and therefore destroy God. A confusion of the essence or existence of the finite beings with the essence or existence of God would lead us to a contradiction. For, a collection of finite essences, even if numerically indefinite, would nevertheless form a finite being. Nor could God’s existence be the existence of all other existing beings, as Master Eckhart, a famous contemporary of Thomas, taught; for infinite existence is of another order than that of finite existence. Per ipsam puritatem est esse distinctum ab omni esse. — “On account of its purity, God’s existence is distinct from all others” [7]. Thus the Schoolmen not only reject the compenetration of finite beings in a single whole (VIII, A and X, A) but also their compenetration with God. They deny monism in all forms. Creation ex nihilo by an act of free will is the only theory which can satisfy the exigencies of the metaphysics of reality as it actually is. In addition to the finite there must exist the Infinite, which can only be infinite on condition that it remains forever other than the finite, while at the same time the finite remains forever in dependence upon the infinite.

Since the principle of causality does not involve the notion of time, a creation for all eternity is not contradictory. On this subject, which was warmly debated in the thirteenth century, Thomas wrote: “It cannot be proved that man, or heaven or stones did not always exist” [8].

God’s knowledge is perfect and identical with His essence. It must extend not merely to His own being, but to all other possible essences. God’s knowledge and government of the universe is dealt with in the theory which has been called the ‘system of laws’ [9]. Thomas Aquinas there sets forth by way of synthesis the relations of subordination and dependence of contingent beings upon God. The eternal law (lex aeterna) is the plan of Providence such as it exists in the infinite knowledge of God. This plan is reflected in each and every being of the universe in a way conformable to its particular nature, and thus constitutes the ‘natural law.’ The effect of this lex naturalis is to lead each being to exercise its activities in such a way as to lead to its end, and so to contribute to the whole plan of Providence. It is blind and fatalistic in inferior beings, but in the case of man it is known by the reason, and it is in the power of human liberty to live accordance with it or the contrary. Lex naturalis nihil aliud est quam participatio legis aeternae in rationali creatura [10]. — “The natural law (of mankind) is simply a reflection of the eternal law in a rational creature.” We shall see shortly what a close relation there is between the natural human law and morality, and why it is that all positive laws ought to be based upon the natural law (XIII, B, XV, G).

D. Conclusion

To Thomas Aquinas, the existence of God is not a truth which is immediately evident, but one requiring demonstration. We do not know Him in the manner in which we know, for example, the principle of contradiction or our own existence, but we have to view Him through the thick veil of the world of sense reality, which is between Him and us. Likewise, a reasoning process alone enables us to know some aspects, or attributes, of God’s Infinity.

Is such a knowledge of God anthropomorphic? Yes and no. Yes, in the sense that if we wish to say anything at all concerning God we must do so in a human way. No, inasmuch as we are fully aware of the inadequate and limited application of the ‘names’ which we give to the Godhead.



  1. Summa Theol., Ia, q. 2, art. 3. Prima via.

  2. Ibid. Tertia via.

  3. De Veritate, q. 2, art. 2.

  4. We must not confuse real Infinite, or God, which means pure perfection, with mathematical infinity, which deals with number and quantity.

  5. Maurice de Wulf, Civilization and Philosophy in the Middle Ages (Princeton University Press, 1922), pp.216-217.

  6. Ego sum qui sum. Exodi, III.

  7. De ente et essentia, cap. vi.

  8. Summa Theol., Ia, q. 46, art. 2. Mundum non semper fuisse sola fide tenetur, et demonstrative probari non potest.

  9. Ibid., Ia IIae, q. 90-97.

  10. Ibid., Ia IIae, q. 91, art. 2.

The late Dr. Jonathan Dolhenty was the Founder and President of The Center for Applied Philosophy and the Radical Academy, and is Honorary Philosophy Editor at The Moral Liberal. The Moral Liberal has adopted these projects beginning with a republishing and preserving of all of Dr. Dolhenty’s work.