It is not our purpose, here, to give even the outlines of a treatise on God; this would take us beyond the limits we placed upon our study, intended to be no more than a general introduction to metaphysics. Thus, with the preceding considerations on causality we have for all practical purposes come to the end. What follows is but by way of summation, presented, however, with a view to showing that the thesis of a first cause, of a being that exists of itself, is not an alien accretion to the Thomist philosophy of being but its logical crown and consummation.
We saw, at the outset, that the first presentation to the intellect is that of being. Proceeding to a more formal consideration of being, we detailed its structure and determined its properties, the transcendentals. Next, we attended to those special modes of being that are most familiar, the categories or predicaments, and saw that substance is the fundamental mode, from which the others issue according to a certain ontological sequence. Came then the analysis of change, which opened up a new vista on being, its distinction into act and potency. And then, to account for the limitation and multiplicity of being, its real composition of essence and existence was found imperative.
The multiplicity of being leads into our final considerations: on the first cause, on being that exists of itself. Reflecting on the beings of experience, we cannot but mark their imperfection, their essential poverty and insufficiency, unable as they are to account for themselves. They change, they are limited; and though they have being, they have it not of their nature, of themselves, but are dependent through and through, radically. It is just this lack, this indigence of being that looks to the existence of a first being, cause of all others. To this end, the various proofs. From being that is moved we are inexorably led to being that is not moved, the first unmoved mover; from being that depends on the efficient causality of another, to a first efficient cause; from contingent being, to a necessary being; from imperfect being, to a perfect being; from beings which tend toward an end, to a supreme ordaining intelligence. By whatever approach, the term is the same; the insufficient leads of necessity to the self-sufficient, whose name is God, whose sufficiency supplies for the insufficiency of all that is not God.
But to round out the Thomistic metaphysics of being two further points should be brought home: first, that God's essence is his being or, which comes to the same, his being is of itself (per se); 17 and second, that every other being is necessarily a being created by God, or being by participation.18 Either way, then, whether from God to creatures or from creatures to God, the science of being comes full circle.19
That God's essence, to take the first point, is the same as his being is readily shown. In creatures, as we have seen, essence and existence are necessarily distinct. But in God they are necessarily identical. For God is the first efficient cause and therefore cannot have received existence from another. Nor can he have received it from himself - nothing causes itself. Consequently, existence must be his by nature or essence. Devoid, moreover, of all potentiality, there can be nothing in his essence save the pure act of his existence. The first existent, God in short can but be by his essence, and this in virtue of the very laws of participation. Impossible, then, that in God essence be one thing and existence another.20
Turning to creatures, we must conclude that every being that is not God must have been created by God. For, when a thing is found to exist in a subject by participation, it must have been caused by a being in which this thing exists of itself. But God is the being that exists of itself, and of such being there can be but one. It follows that all things that are not God are not their being (their nature is not their existence), but only participate in being. Consequently, and finally, whatever is diversified according to its participation in being is caused by a first being which is perfect not by participation or degrees, but absolutely.21
Viewed against this perspective of Creator and creature, the whole metaphysic of the real appears in striking simplicity. At the summit is the principle to the whole, being that exists of itself, whose essence is to exist. Below, in radical dependence on this being, are the beings that cannot exist of themselves and therefore hold their existence from the being that does so exist. Such are the essentials, epitomized for us in the third of the 24 Thomistic Theses enunciated by the Sacred Congregation of Studies: "Wherefore, by the absolute nature of his existence, God alone subsists, He alone is utterly simple. All other things which participate in his being have a nature that restricts their being, and are composed of the really distinct principles of essence and existence." 22
Just how, on the other hand, St. Thomas conceives this participation in the being of God, how it procures the creature the proper ontological status, all this is here left unsaid. These particulars are better reserved to the treatise on God, where being is scrutinized more thoroughly than is feasible in the introductory metaphysics. Suffice it to have brought the reader to the mere threshold of these further perspectives.23
The whole philosophy of being stems on the recognition that in God there is identity of essence and existence; whence it is that he is the fullness of being, fullness in which all other beings but participate. In the following passage St. Thomas, in a mood not unlyrical, finds this sublime (his word) truth adumbrated in the revelation God made of his name to Moses; it is a passage that will serve as fitting conclusion to our study:
This sublime truth [he writes] Moses was taught by the Lord; for when he asked the Lord: "If the children of Israel should say to me: 'What is His name? what shall I say to them?" the Lord answered: "I am who am. . . . Thus shalt thou say to the children of Israel: He who is hath sent me to you" (Exod. 3:13,14), thus declaring His own proper name to be He who is. Now, every name is appointed to signify the nature or essence of a thing. Wherefore it follows that God's very existence itself is His essence or nature.24