Essence and Existence are the same in God (Aesity)
This doctrine is more formally referred to as the Aesity of God. Essentially, aesity means self-existence. Aesity explains the metaphysical nature of God as a purely self-existent being that exists in complete actuality. God is not a being that is created by another god; neither does God create himself into existence. Rather, God has always existed as an unchanging, completely actualized being.
St. Thomas seeks to show that God is his own existence as well as his own essence. God has his Being of himself and to himself such that he is Absolute being and the definition of existence. Since Gods essence is his nature and Gods existence is the same as his essence it follows that God is existence.
The doctrine of Gods essence as existence has not been formally defined by the Church. However, the doctrine of essence as existence is well founded in Exodus 3:14 when God declares his true name to Moses: IAM WHO I AM. The Fathers of the Church agree that Exodus 3:14 records God declaring himself as pure and simple Being. The metaphysical essence of God is existence.
The doctrine is at the root of the definition of all of Gods other perfections because if God is Absolute Being he must logically contain in himself all perfections of being.
There are no heresies that directly relate to this doctrine. However, all heresies that reject the existence of a divine God, the perfection of God, the unity of God, and the simplicity of God, implicitly oppose the doctrine of aesity.
P1. Whatever a thing has besides its essence must be caused by the constituent principles of that essence or by some exterior agent.
P2. Consider a created thing. It is impossible for a created things existence to be caused by its essential constituent principles because nothing can be the sufficient cause of its own existence if its existence is caused.
C1. Therefore, a created thing has its existence different from its essence.
P3. God is the first efficient cause.
C2. As the first efficient cause, anything God has cannot be due to an exterior agent. C3. Gods essence is identical to his existence.
P1. Existence is that which makes every form or nature actual. Existence is actuality as opposed to potentiality.
P2. There is no potentiality in God; only actuality.
P3. God is his essence.
C1. Since God is actuality his essence is existence.
- If Gods essence and existence are the same, then God has nothing added to him. Therefore, God is being in general and is universally predicated of all things (heresy of pantheism).
Reply: God is existence to its fullest and simplest extent. All other beings participate in his existence on a contingency and thus do not posses the nature of God. Therefore, no being can be said to be a god or share a part in godhead since they exist solely on a contingency. Gods essence precludes any addition absolutely. Prime matter (of which all material things are composed) has a nature in which nothing is required to be added to it: but not absolutely. Thus prime matter is predicated of all material things, but God is not.
- It has been shown that we can know that God exists, but we cannot understand his nature. If this is true then Gods nature and existence cannot possibly be the same thing or we would understand his nature.
Reply: We understand the proposition: God exists. We also understand the proposition: God is. Thus for both propositions, we understand them in the sense that we have joined a subject and a predicate and understand both terms. However, we do not understand the essence of either proposition. Thus we understand Gods existence and nature in the first sense but not in the deeper second sense.
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