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The doctrine of divine simplicity has been a cornerstone of Christian dogmatics for most of the history of the Church, and it is currently enjoying something of a renaissance. Several recent academic works have tried to push it to the center of academic theological conversation.*

Still, I would imagine most readers find it to be a rather abstract notion that doesn’t seem to make much of a difference for them. It’s exactly that thought that I would like to address in this essay. Using the theological arguments of Athanasius of Alexandria, I will demonstrate how the doctrine of divine simplicity sits right at the center of the doctrine of the Trinity.

Athanasius of Alexandria

Athanasius of Alexandria was one of the most important theologians of the Fourth Century. While he did not become a bishop until shortly after the Council of Nicaea (and thus he most likely was not an active participant in the council itself), he quickly became its greatest defender.

Many people link Athanasius with the term homoousios. This is the famous watchword, found in the Nicene Creed, that the Son of God is “of one substance with the Father.” The various Arian parties tended to reject this term, arguing that the Son was inferior and subordinate to the Father. This way of understanding the debate is fine as far as it goes, but contemporary readers will notice that Athanasius does not actually use the term homoousios as much as you might expect.

Instead, Athanasius prefers to argue that the Son of God is born or “begotten” from God the Father. To be a Son means to be born from a Father, and Christ was born from God. Athanasius believed that this was the primary biblical way to talk about Jesus.

Viewed on a human or earthly level, this language seems to give ground to the Arian position. After all, aren’t sons necessarily inferior to their fathers? Aren’t fathers always “before” sons?

This is where the doctrine of divine simplicity comes in. For Athanasius, the eternal Son of God is indeed born from the Father, but the Father has a simple essence. And if the Father is simple, then He cannot admit of distinctions of time and space. He cannot give a part of His essence to His Son. He must give the whole thing.

Defining Divine Simplicity

The easiest explanation is of divine simplicity is that God is not made up of parts. Simple is being used to mean the opposite of “composite” or “complex.” God cannot be divided into distinct sections or segments. There is no “greater” or “lesser” in God, nor are there accidental attributes which could be removed from God while still retaining an essential core.

God is Who He is, and God is That He is (Ex. 3:14). The Apostle John even goes so far as to identify God with His attribute of love, writing “God is love” (1 John 4:8) and “he who abides in love abides in God” (1 John 4:16).

Athanasius explains simplicity in several places. In his very first book he writes, “For men, composed of parts and made out of nothing, have their discourse composite and divisible. But God possesses true existence and is not composite…” (Contra Gentiles, 41).

Athanasius explicitly denies that God can be said to have “accidents” within Him (De Decretis, 5.22). In one of his final writings, he puts things this way:

For God, who compounded all things to give them being, is not compound, nor of similar nature to the things made by Him through the Word. Far be the thought. For He is simple essence, in which quality is not, nor, as James says, “any variableness or shadow of turning.” (To the Bishops of Africa, 8)   

Divine Simplicity and Eternal Generation

Athanasius then applies this notion to the concept of the divine Son’s generation from the Father. To be a Father would require one to have an offspring, and to be a Son likewise requires having a Father. Thus, the question arises, how is it that God is eternally father?

If God could only become a father if He created, then the implication would be that God could only be Himself with the addition of creation. God would be, in a sense, dependent on creation. Contrary to this unthinkable suggestion, Athanasius argues that God is eternally Father.

Likewise, the Son has always been a Son to the Father. There was never a time or even a thought “when He was not.” And the way that Athanasius explained all of this was to connect the eternal generation of the Son to the doctrine of divine simplicity.

While it’s true that earthly fathers preexist their sons and grant life to their sons that their sons otherwise would not and could not have, this is not true for God because God is of a wholly different essence. God has no time or space within Him. Indeed, God has no parts. Athanasius explains:

“For the offspring of men are portions of their fathers, since the very nature of bodies is not uncompounded, but in a state of flux, and composed of parts; and men lose their substance in begetting, and again they gain substance from the accession of food. And on this account, men in their time become fathers of many children; but God, being without parts, is Father of the Son without partition or passion; for there is neither effluence of the Immaterial, nor influx from without, as among men; and being uncompounded in nature, He is Father of One Only Son.” (De Decretis, 3.11)

Notice the mention of God “being without parts.” The quality of God’s essence holds the logic together.

In fact, since divine simplicity entails that all of God is all of God, this means that when the Father “gives” something of Himself to the Son, He gives all of Himself to Him. This is how Athanasius explains John 5:26, “For as the Father has life in Himself, so He has granted the Son to have life in Himself.” Athanasius writes:

“It is necessary, then, that we should perceive that in the Father reside Everlastingness, Eternity, Immortality. Now these reside in Him not as adventitious attributes, but, as it were, in a well-spring they reside in Him, and in the Son. … For what belongs to the Father, belongs to the Son.” (On Luke 10:22 and Etc., 4). 

This means that when the Father generates the Son, He does not give a part of Himself to His Son. God does not delegate a portion or percentage of deity to His Son. He gives His entire nature. Far from being a challenge to the full deity of Christ, the eternal generation of the Son entails the total equality of nature between the Father and the Son in God.


The doctrine of divine simplicity is an explanation of the very nature of God. It explains what God is like, what kind of God He is. This is a philosophical doctrine, to be sure, but it was a philosophical doctrine that allowed Athanasius to defend the doctrine of the Trinity itself, the full and equal deity of the Son of God.

Understanding divine simplicity will help modern Christians better understand their own faith as they better understand what they mean when they say that the eternal Son of God was “born” or “begotten” of the Father and also that the Son is equal to the Father in essence, glory, and power. Thanks to simplicity, we can say that the Son of God is very God of very God indeed.

*See for example: God Without Parts by James Dolezal, God in Himself by Steve Duby, and The Lord is One ed. by Minich and Kamel.