God's Nature Cannot Be Separated from His Existence
Aquinas (Thomas)
Source: Rowe & Wainwright - Philosophy of Religion
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First Article. Whether The Existence Of God Is Self-Evident?

    ... A thing can be self-evident in either of two ways: on the one hand, self-evident in itself, though not to us; on the other, self-evident in itself, and to us. A proposition is self-evident because the predicate is included in the essence of the subject: e.g., Man is an animal, for animal is contained in the essence of man. If, therefore, the essence of the predicate and subject be known to all, the proposition will be self-evident to all; as is clear with regard to the first principles of demonstration, the terms of which are certain common notions that no one is ignorant of, such as being and non-being, whole and part, and the like. If, however, there are some to whom the essence of the predicate and subject is unknown, the proposition will be self-evident in itself, but not to those who do not know the meaning of the predicate and subject of the proposition. Therefore, it happens, as Boethius says, that there are some notions of the mind which are common and self-evident only to the learned, as that incorporeal substances are not in space. Therefore I say that this proposition, God exists, of itself is self-evident, for the predicate is the same as the subject, because God is His own existence as will be hereafter shown. Now because we do not know the essence of God, the proposition is not self-evident to us, but needs to be demonstrated by things that are more known to us, though less known in their nature—namely, by His effects...

Third Article. Whether God Is The Same As His Essence Or Nature?
  1. Objection 1. It seems that God is not the same as His essence or nature. For nothing is in itself. But the essence or nature of God—i.e., the Godhead—is said to be in God. Therefore it seems that God is not the same as His essence or nature.
  2. Objection 2. Further, the effect is assimilated to its cause; for every agent produces its like. But in created things the suppositum is not identical with its nature; for a man is not the same as his humanity. Therefore God is not the same as His Godhead.
    • On the contrary, it is said of God that He is life itself, and not only that He is a living thing: I am the way, the truth, and the life (Jo. xiv. 6). Now the relation between Godhead and God is the same as the relation between life and a living thing. Therefore God is His very Godhead.
    • I answer that, God is the same as His essence or nature. To understand this, it must be noted that in things composed of matter and form, the nature or essence must differ from the suppositum, for the essence or nature includes only what falls within the definition of the species; as humanity includes all that falls within the definition man, for it is by this that man is man, and it is this that humanity signifies, that, namely, whereby man is man. Now individual matter, with all the individuating accidents, does not fall within the definition of the species. For this particular flesh, these bones, this blackness or whiteness, etc., do not fall within the definition of a man. Therefore this flesh, these bones, and the accidental qualities designating this particular matter, are not included in humanity; and yet they are included in the reality which is a man. Hence, the reality which is a man has something in it that humanity does not have. Consequently, humanity and a man are not wholly identical, but humanity is taken to mean the formal part of a man, because the principles whereby a thing is defined function as the formal constituent in relation to individuating matter. The situation is different in things not composed of matter and form, in which individuation1 is not due to individual matter—it is to say, to this matter—but the forms themselves are individuated of themselves. Here it is necessary that the forms themselves should be subsisting supposita. Therefore suppositum and nature in them are identified. Since, then, God is not composed of matter and form, He must be His own Godhead, His own Life, and whatever else is so predicated of Him.
  3. Reply Objection 1. We can speak of simple things only as though they were like the composite things from which we derive our knowledge. Therefore, in speaking of God, we use concrete nouns to signify His subsistence, because with us only those things subsist which are composite, and we use abstract nouns to signify His simplicity. In speaking therefore of Godhead, or life, or the like as being in God, we indicate the composite way in which our intellect understands, but not that there is any composition in God.
  4. Reply Objection 2. The effects of God do not imitate Him perfectly, but only as far as they are able. It pertains to defect in imitation that what is simple and one can be represented only by a multiplicity. This is the source of composition in God's effects, and therefore in them suppositum is not the same as nature.

Fourth Article. Whether Essence And Being Are The Same In God?
  1. Objection 1. It seems that essence and being [esse] are not the same in God. For if it be so, then the divine being has nothing added to it. Now being to which no addition is made is the being-in-general which is predicated of all things. Therefore it follows that God is being-in-general which can be predicated of everything. But this is false. For men gave the incommunicable name to stones and wood (Wisd. xiv. 21). Therefore God's being is not His essence.
  2. Objection 2. Further, we can know whether God exists, as was said above, but we cannot know what He is. Therefore God's being is not the same as His essence—that is, as His quiddity or nature.
    • On the contrary, Hilary says: In God being is not an accidental quality but subsisting truth. Therefore what subsists in God is His being.
    • I answer that, God is not only His own essence, as has been shown, but also His own being. This may be shown in several ways. First, whatever a thing has besides its essence must be caused either by the constituent principles of that essence (like a proper accident that necessarily accompanies the species—as the faculty of laughing is proper to a man—and is caused by the constituent principles of the species), or by some exterior agent,—as heat is caused in water by fire. Therefore, if the being of a thing differs from its essence, this being must be caused either by some exterior agent or by the essential principles of the thing itself. Now it is impossible for a thing's being to be caused only by its essential constituent principles, for nothing can be the sufficient cause of its own being, if its being is caused. Therefore that thing, whose being differs from its essence, must have its being caused by another. But this cannot be said of God, because we call God the first efficient cause. Therefore it is impossible that in God His being should differ from His essence.
    • Second, being is the actuality of every form or nature; for goodness and humanity are spoken of as actual, only because they are spoken of as being. Therefore, being must be compared to essence, if the latter is distinct from it, as actuality to potentiality. Therefore, since in God there is no potentiality, as shown above, it follows that in Him essence does not differ from being. Therefore His essence is His being. Third, just as that which has fire, but is not itself fire, is on fire by participation, so that which has being, but is not being, is a being by participation. But God is His own essence, as was shown above. If, therefore, He is not His own being, He will be not essential, but participated, being. He will not therefore be the first being—which is absurd. Therefore, God is His own being, and not merely His own essence.
  3. Reply Objection 1. A thing-that-has-nothing-added-to-it can be understood in two ways. Either its essence precludes any addition (thus, for example, it is of the essence of an irrational animal to be without reason), or we may understand a thing to have nothing added to it, inasmuch as its essence does not require that anything should be added to it (thus the genus animal is without reason, because it is not of the essence of animal in general to have reason; but neither is it of the essence of animal to lack reason). And so the divine being has nothing added to it in the first sense; whereas being-in-general has nothing added to it in the second sense.
  4. Reply Objection 2. To be can mean either of two things. It may mean the act of being, or it may mean the composition of a proposition effected by the mind in joining a predicate to a subject. Taking to be in the first sense, we cannot understand God's being (or His essence); but only in the second sense. We know that this proposition which we form about God when we say God is, is true; and this we know from His effects, as was said above.


From Summa Theologica, Part 1, Questions 2 and 3. Hard copy filed in "Various - Heythrop Essays & Supporting Material (Boxes)".

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