Whether Essence and Existence Are the Same in God?
Objection 1: It seems that essence and existence 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 universal being 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" (Wis. 14:21).
Therefore God's existence is not His essence.
Obj. 2: Further, we can know _whether_ God exists as said above
(Q. 2, A. 2); but we cannot know _what_ He is. Therefore God's
existence is not the same as His essence--that is, as His quiddity or
nature.
_On the contrary,_ Hilary says (Trin. vii): "In God existence is not an
accidental quality, but subsisting truth." Therefore what subsists in
God is His existence.
_I answer that,_ God is not only His own essence, as shown in the
preceding article, but also His own existence. 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
property 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 existence of a thing
differs from its essence, this existence must be caused either by some
exterior agent or by its essential principles. Now it is impossible
for a thing's existence to be caused by its essential constituent
principles, for nothing can be the sufficient cause of its own
existence, if its existence is caused. Therefore that thing, whose
existence differs from its essence, must have its existence caused by
another. But this cannot be true of God; because we call God the first
efficient cause. Therefore it is impossible that in God His existence
should differ from His essence. Secondly, existence is that which
makes every form or nature actual; for goodness and humanity are
spoken of as actual, only because they are spoken of as existing.
Therefore existence must be compared to essence, if the latter is a
distinct reality, as actuality to potentiality. Therefore, since in
God there is no potentiality, as shown above (A. 1), it follows
that in Him essence does not differ from existence. Therefore His
essence is His existence. Thirdly, because, just as that which has
fire, but is not itself fire, is on fire by participation; so that
which has existence but is not existence, is a being by participation.
But God is His own essence, as shown above (A. 3); if, therefore, He
is not His own existence He will be not essential, but participated
being. He will not therefore be the first being--which is absurd.
Therefore God is His own existence, and not merely His own essence.
Reply Obj. 1: A thing that has nothing added to it can be of
two kinds. 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 to
lack reason. And so the divine being has nothing added to it in the
first sense; whereas universal being has nothing added to it in the
second sense.
Reply Obj. 2: "To be" can mean either of two things. It may
mean the act of essence, 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
existence nor 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 (Q. 2, A. 2).
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