In discussing the oneness of God, two particular doctrines often come into mind: divine simplicity and divine aseity. These are closely related, and the same arguments may be used to establish both. In this post, I wish to first present arguments for the simplicity and aseity of God; then I will discuss the implications of these truths.
Thomas Aquinas’s Arguments
The influential medieval Catholic theologian and philosopher Thomas Aquinas was an advocate for divine simplicity and divine aseity and presented some arguments for these doctrines in his Summa Theologica (“Theological Summary”).
His argument for divine aseity, the absolute independence or self-existence of God, was succinctly stated in the Fourth Article of the Third Question in the First Part of his Summa as follows:
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.
In other words, Aquinas was saying that nothing can cause itself and that because God is by definition uncaused, His existence is not separate from His essence. This means that God exists of and in Himself.
Most of his arguments for divine simplicity follow from his five arguments for the existence of God. Since God is the first uncaused Cause, He cannot Himself be caused; but as Aquinas states in the Seventh Article of the Third Question of the First Part in his Summa: “every composite has a cause, for things in themselves different cannot unite unless something causes them to unite.” He also argued in this same section that “in every composite there is something which is not it itself.”
The cosmological argument for God’s existence, then, leads directly and logically to the idea that God is absolutely simple so that if the cosmological argument is true, then it follows that God’s simplicity is true. This is because the cosmological argument, in its various forms, demonstrates, not only God’s existence, but also that God was the first Cause, who was Himself uncaused.
Furthermore, to claim that God is composed of something which is not Himself is to imply that something existed in addition to God from eternity past.
God as the Necessary Being
Building off of Ibn Sina’s ontological argument for God’s existence, God’s absolute independence (divine aseity) and His absolute oneness (divine simplicity) may be deduced. The world and the things which make up the world are contingent, for they are caused. That which is contingent receives its existence from another. It is impossible for there to be an infinite chain of contingent causes in actuality. Thus, there must be an initial cause which was not contingent, which is to say that it was necessary. (A necessary existent is that which exists independently so that it does not require anything for its existence. Or in modal logic, it is that which is impossible to not exist.) This necessary existent must have had a free will for it to have caused anything of itself and without outside influence. Therefore, this necessary existent also had a mind, for that which has a will has a mind. This necessary Existent, then, may be rightly called God.
From this, we gather that God is a necessary Being. If God is necessary, He is necessarily self-existent; otherwise, He would be contingent. Thus, the doctrine of divine aseity may be easily deduced from the ontological argument for God’s existence.
As for the absolute oneness of God, it follows that if God is a necessary Being, He cannot be dependent on anything; for that which is dependent is contingent. If God is composed of parts, or attributes, or of a plurality of anything else, then He is dependent on those parts. Thus, God cannot be composed of a plurality of things.
Implications of Divine Aseity
If God is self-existent, then this implies that God does not need anyone or anything. All things besides Him do not exist because they must exist, but they exist because God so willed that they exist. This means that God in some way and for some reason desires that we exist. For us, this should evoke a sense of awe and great reverence, for our very existence flows from God’s uninfluenced desire.
Divine aseity also implies that God does not have attributes but rather is His attributes, or rather is His attribute (singular). This is because God cannot be dependent on anything besides Himself, on account of His self-existence. If God were to possess attributes, He would have parts besides Himself in a way that He would be dependent on those things.
Implications of Divine Simplicity
The implications of divine simplicity can be complicated. A question that may arise in response to this doctrine is what we should do with God’s attributes. In light of divine aseity, God does not have attributes but rather is His attributes. In light of divine simplicity, God only has, or rather is, one attribute; and this one attribute is God Himself. This can be very confusing, but it follows logically from the absolute oneness of God.
The Trinity in Light of Divine Simplicity and Divine Aseity
An important implication of God’s simplicity and of His aseity is in regard to the doctrine of the Trinity. If God is not composed of parts, which is in the very definition of divine simplicity and is an implication of divine aseity, then each member of the Trinity cannot be considered a part of God. Now, most Christians have historically rejected this view of the Trinity, that the Father, the Son, and the Holy Spirit are different parts of the whole of God. Most Trinitarians hold that each member of the Trinity is wholly God.
However, the divine simplicity of God would seem to imply that even this version of the Trinity is not an acceptable view of God, since there is still differentiation within God. There is no logical reason to say that plurality in persons is a justifiable exception to divine simplicity. Furthermore, the transitive law in logic should be considered. This law states that if two identities are both equal to another identity, then both of those identities are also equal to each other. Of course, this law can be expanded to include three identities in order to apply to the doctrine of the Trinity.
Thus, the most logical view of the Trinity seems to be the modal view, which holds that God is three different modes. In other words, the Father, the Son, and the Holy Spirit, in this view, would not be separate persons, but different personalities, that is, different modes of manifestation of the same person. However, this is unfounded, because the Bible clearly does not imply this. In fact, it would imply against it. Jesus prayed to the Father; thus, he could not have been the Father, unless Jesus was praying to a different mode of himself, which would make him mad.
Furthermore, numerous times throughout the New Testament, the Father and Jesus are clearly indicated to be different persons. For instance, in John 16:28, Jesus allegedly said: “I came from the Father and have come into the world, and now I am leaving the world and going to the Father” (John 16:28 ESV). Furthermore, in Colossians, Paul wrote: “If then you have been raised with Christ, seek the things that are above, where Christ is, seated at the right hand of God” (Col. 3:1 ESV). It seems nonsensical to say that Jesus sat at the right hand of a different one of his personalities. Clearly, the New Testament does not teach modalism.
It would seem then that the doctrine of the Trinity as traditionally and commonly understood by Trinitarians is not logically sound, and modalism is not based on anything except an attempt to make the Trinity logical. Even then, the view of modalism is a bit far fetched, since it would seem to turn God into a madman.