St Thomas's Proof for God's Existence in the De Ente

In the abundant works of the Angelic Doctor St Thomas Aquinas, many philosophers tend to emphasize St. Thomas’s five ways for demonstrating God’s existence as is presented in his work the Summa Theologiae. While they are profound, they are not the only ways for God’s existence St. Thomas presents in all his works. In his work titled De Ente et Essentia, which in english is On being and essence, St. Thomas covers the metaphysics of the essence and existence distinction. Essence can simply be defined as what a thing is, while existence or being, is that a thing is in reality. Take Man for instance, the essence of a man is that he is a rational animal. But the fact that he does or doesn’t exist is not part of his essence, it's something really distinct from it. This will be the subject of discussion today, and it's a distinction which St. Thomas utilizes and comes to the conclusion of God’s existence. Now to demonstrate the distinction between essence and existence, St. Thomas states:“Whatever is not in the concept of the essence or the quiddity comes from outside the essence and makes a composition with the essence, because no essence can be understood without the things that are its parts. But every essence or quiddity can be understood without understanding anything about its existence: I can understand what a man is or what a phoenix is, and nevertheless not know whether either has existence in reality.”

St. Thomas gives the scenario of considering the various essences of things, the essence being that of man or humanity, the second is that of a phoenix bird which is merely legendful and doesn’t exist. But nonetheless, simply knowing what it is to be a man or a phoenix bird does not allow the person to know whether or not they exist. As by the fact that I can know the essence of a phoenix bird, if existence were part of its essence, then I would be able to tell if it existed or not. St. Thomas then gives the hypothetical of a being in which its essence and existence are identical to further prove the real distinction between essence and existence: “Therefore, it is clear that existence is something other than the essence or quiddity, unless perhaps there is something whose quiddity (essence) is its very own existence, and, if so, this thing must be one and primary… But if we posit a thing that is existence only, such that it is subsisting existence itself, this existence will not receive the addition of a difference. For, if there were added a difference, it would be not only existence, but existence and also some form beyond this. Much less would such a thing receive the addition of matter, for then the thing would be not subsisting existence but material. Hence, it remains that a thing that is its own existence cannot be other than one, and so in every other thing, the thing’s existence is one thing, and its essence or quiddity or nature or form is another.” 

Here St. Thomas argues that if there was a being whose essence is its existence, that thing would be subsistent existence itself (Ipsum esse subsistens). Further there could only be one such being that is identical to existence itself. This is the case as if there were something to differentiate this self-subsistent being from another self-subsistent being, then that being’s essence would be identical to existence, plus whatever else it may have predicated of it. So in sum, it wouldn’t actually be identical to existence, as it would have another feature, therefore since there can’t be any distinguishing feature to differentiate the “multiple beings which are self existent”, they would all be identical to each other, and therefore only one could actually exist. Therefore, anything that is not this one being, since only one can exist would necessarily have to be composed of essence and existence, so for example, because a man can be differentiated among other men, their essence must be distinct from their existence.

After demonstrating the real distinction between essence and existence in compound beings, St. Thomas continues further: “Everything that pertains to a thing, however, either is caused by the principles of its own nature, as risibility in man, or else comes from some extrinsic principle, as light in the air from the influence of the sun. Now, it cannot be that existence itself is caused by the very form or quiddity of the thing (I mean as by an efficient cause), because then the thing would be its own efficient cause, and the thing would produce itself in existence, which is impossible.”

St. Thomas gives us a dilemma, either existence is caused by a being's nature, or existence is something which it receives from an external source. On the first point, St. Thomas argues that existence is not brought forth by a thing's nature, because then it would be its own efficient cause of existence, which is illogical since that being doesn’t exist yet to cause its own existence. Cardinal Cajetan explains it as such: “That it is impossible that some being should effect its own proper existence is evident from this, that it would then follow that it would exist before it would exist. From the fact that it would cause, it would exist, for every efficient cause exists; from the fact that its own proper existence (esse) would cause its own existence (existere), it would follow upon causality of that. Thus it would exist before it would exist.” (Commentary on the De Ente).

On this point, the only other option is that existence is derived externally from another. St Thomas states: “Therefore, everything the existence of which is other than its own nature has existence from another. And since everything that is through another is reduced to that which is through itself as to a first cause, there is something that is the cause of existence in all things in that this thing is existence only. Otherwise, we would have to go to infinity in causes, for everything that is not existence alone has a cause of its existence, as was said above. It is clear, therefore, that the intelligences are form and existence and have existence from the first being, which is existence alone, and this is the first cause, which is God.”

The Angelic Doctor posits what is known as a per se causal chain in which each member of the causal series receives existence from the previous member. This causal chain is not one which goes back into the past, but it's one where each member relies on the previous member at any moment, so for example a rock being moved by a stick being moved by hand. And so each member in this causal chain has existence in virtue of it receiving it from the first cause of the chain or that being which just is existence itself, which we know of as God. And so the reasoning for the causal chain to not go onto infinity, is that each member is a secondary cause and does not possess existence of themselves, but possesses it only in virtue of a primary cause or being which has it of itself. This being would have to be existence itself, as if its essence and existence were really distinct, then the causal chain would go on still to infinity. Fr. Garrgiou-Lagrange comments on infinite regress and therefore refutes it as well, he states: “But such infinite regress is absurd in a series necessarily subordinated, as, for example, in the following: "the moon is attracted by the earth, the earth by the sun, the sun by another center, and thus to infinity. Such regress, we must say, is absurd. If there is no first center of attraction, here and now in operation, then there would be no attraction anywhere.” (Reality: A synthesis of Thomistic thought, ch. v)

St. Thomas then concludes that the primary cause of this chain must be ipsum esse subsistens or self-subsistent being/ existence. Many divine characteristics or perfections follow from the primary cause being existence itself, for example, it would have to be eternal since it can’t begin or seize to exist. It would also have to be immutable or changeless since if it had any potential to change, it would be an addition to that being's existence or a change to its existence which is impossible, nonetheless St. Thomas already demonstrated that such a being is existence only and cannot have any additions to its essence. From the conclusion of the argument, objections like existential inertia are refuted, since in virtue of the members of the per se causal chain, they would need the primary cause to exist at any moment for their existence. Suffice it to say, we have concluded that there exists a being which just is existence itself and has the power to cause existence in others and this is what we know of as God.