The Essence-Existence Distinction Under Thomas Aquinas

One of my previous blogs discussed the doctrine of Divine Processions and specifically the procession of the Son by way of knowing was explained. In that blog I wrote, 

“However, God knows himself perfectly and he is the only thing that can possibly understand his own essence. In his act of understanding himself it will be a perfect image with the same essence as it will be identical as it will be a reflection of his essence. Therefore, the Son proceeds by way of knowing. Knowledge is a procession. The reason why it becomes a person is because it is the perfect image of the divine essence.”

This made me ask why this is the case? Could God imagine anything such as a unicorn and “by way of knowing” it exists? But then I continued to think and it hit me! Perhaps the difference between the Logos and a unicorn is that the former procession presupposes that existence is part of essence. God could imagine a perfect unicorn but that alone would not make it exist, however when it comes to the second person of the Godhead in Christianity, since they have the same essence, the Son becomes begotten of the Father and therefore exists. Therefore, the difference between a unicorn and the Son is that the Son, who is also called God, in his divine essence has existence otherwise he would be like the unicorn.

Then I found out that the distinction between essence and existence is crucial in Thomist theology. The Thomist perspective holds that in God, essence and existence are identical. This is because like Aristotle and Ibn Sina, Thomas Aquinas also holds to the doctrine of Divine Simplicity. For created beings, there is an essence-existence distinction. Each created thing has its essence, which is what it is by definition, and its existence, which is the act of being granted by God. I have many blog posts about Divine Simplicity including its critiques from Islamic theologians and John Duns Scotus but in short, according to the Stanford Encyclopedia, 

“God is simple in that God transcends every form of complexity and composition familiar to the discursive intellect. One consequence is that the simple God lacks parts…There is also no real distinction between God as subject of his attributes and his attributes. God is thus in some sense identical to each of his attributes, which implies that each attribute is identical to every other one.As identical to each of his attributes, God is identical to his nature. And since his nature or essence is identical to his existence, God is identical to his existence.”

A human or a unicorn is not a necessary existence rather it is contingent. Furthermore, the essence of the human soul is its definition not its existence or in other words, the description of the soul does not contain existence, it would contain however immateriality. Its existence is given to it by God. However, the being whose essence contains its existence is God as previously mentioned. Rather, his existence is identical to his essence due to Divine Simplicity. Since his essence is his existence and his existence is his essence, he exists necessarily. The essence of a human being can be known without its existence as a human can cease to exist. Therefore, anything whose existence is separate from its existence received its existence from somewhere and the rational mind knows that there cannot be an infinite regress of beings providing existences to the next. Therefore, there must be a first cause or God whose existence is his essence that gives way to all other existences.

“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.” (Summa Theologica, First Part, Question 3, Article 4)