Today I’m pleased to run this helpful guest post from my friend Andrew Fulford. Given the confusion that has surrounded the recent trinitarian debate, I thought it would be useful to find someone who could write a relatively straight forward post explaining the different terms being tossed around in this debate so far. So this post is going to be a Vox-style explainer answering some of the basic questions that have come up due to the controversy.

What is divine simplicity?

If you have followed the recent upheaval over the Trinity and gender, you may have asked yourself that question. This doctrine was once taken for granted by basically everyone, from the earliest days of the church through to the Reformation and beyond, and only became unfamiliar quite recently. I’m not going to be able to explain all the details of the idea here. My objective is twofold: to give a basic outline of the idea, and to explain why the tradition of classical Christian theism held to it.

The idea can be stated briefly, though negatively: God is not composed of any parts. This includes the obvious physical sense, in that God has no body and so has no corporeal parts, but it also includes a metaphysical meaning. That is, God has no parts even at the more basic level of being. He is not a composite of material and immaterial, like all material substances which have both matter and form; nor is he a composite of body and soul like human beings.

But even further, he is not a composite of essence and existence, as even spirits like angels are. That is, in God there is no distinction between what he is, and that he is. In everything else, there is. Fictional beings are conceivable; there is a “what” that we can talk about when we talk about unicorns and Clark Kent. No longer existent beings also have a what: Trees that have been cut down and pulverized into paper and particle board are intelligible, we know “what” they were, even though they no longer have existence as such.

But God is unique in that this does not apply to him. Rather he is, as Aquinas would say, “subsistent being”. That is, “what” he is does not consist of various kinds of being (say, a substance and then further accidents, both of which are types of being though different types); he is simply being itself, existing independently. And there cannot be more than one “being itself.” If there were, some type of being, i.e. a property of some kind, would have to be added to being itself to distinguish the two. But if such a property were added, neither would be “being itself”, but “being plus …”. Thus God is absolutely uncompounded, and totally one.

Why would the tradition hold to this concept?

They believed that whatever else God was according to scripture and natural revelation, he must be the ultimate Cause, or one could even say Creator, of all things. And if he is, he cannot himself require a cause. Yet, if God were compounded in some way, his compound unity would demand an explanation. If God is more than just being itself, if therefore his “what he is” and “that he is” are not identical but distinct, something would have to give “thatness” (existence) to his “what” (essence). This is impossible with God by definition. So God must be simple.

For those unfamiliar with this idea, several objections to this doctrine might have already occurred to you. Some readers might think this idea is too philosophical to be a native element of Christian theology. But forming this thought raises a more basic question: What is philosophy anyway? Alvin Plantinga argues that in fact it’s really nothing different from “thinking hard.” And it’s hard to mount a biblical objection to thinking hard. The real question, then, should not be whether this idea is too philosophical to be biblical; it should rather be, does thinking hard about what scripture says, what it implies, and what its teaching must presuppose, lead to the idea that God is uncompounded? Well, if the logic of the idea follows from God having to be the uncreated Creator of all things, there’s certainly a prima facie case to be made that thinking hard about scripture does lead to this idea.

And in fact, if it does, then denying that the God of the Bible was simple would be to deny that he was really the Creator. It would be tantamount to the kind of move that some Gnostic philosophies made early in church history, that the God of the Bible was actually a lower-level emanation or effect of the true God. But this does not fit at all with scripture. Indeed, beyond scripture directly stating that God is the source of all things, it also, through King David in Psalm 19 and Paul in places like Romans 1, tells us that “thinking hard” about the created order can lead us to know things about God. And this in turn means that denying simplicity because it just seems “too philosophical” actually entails denying scripture, which tells us to learn about God’s nature from studying his effects in the universe.

Other readers might immediately wonder how this fits with the Trinity, and they are right to raise the question. However, when the Christian tradition spoke of the Trinity, it must be understood that their entire way of explaining it agreed with simplicity. They explained it in such a way that it could be consistent with this idea. If it seems hard to understand how they could do so, they would agree: They taught that the Trinity was a mystery that was beyond complete human comprehension.

They did, however, come up with a way of explaining all the scriptural data that pressed the church to formulate the doctrine of the Trinity, and it should be said, among those data was the explicit scriptural witness to monotheism. Explanations of the threeness of God that amount to teaching there are three divine beings runs up against not simply squaring themselves with simplicity, but also with monotheism. And indeed, the larger argument of the classical tradition would be that those two ideas, divine simplicity and monotheism, are not accidentally linked, but rather are two sides of the same coin.

Related to the Trinity, the phrase “inseparable operations” has arisen more frequently in recent conversations not least due to the work of scholars like Lewis Ayres and Michel Rene Barnes. Divine simplicity entails inseparable operations, in that a simple being with an intellect and will performs an unified operation whenever he operates. The Father, Son, and Holy Spirit share one simple will, and so all activity toward creation bares the mark of that simplicity. The Persons do not cooperate with three harmonious, but separate actions. Rather, they all share the very same acts, because they are all, together and considered separately, the one God.

But it should be honestly stated that there is at least a prima facie difficulty in affirming the whole of the classical doctrine of the Trinity. The struggle is to hold on to both the threeness and oneness without eliding either. As Herman Bavinck explained:

…the great challenge facing us with this dogma is to see to it that the unity of the divine essence does not cancel out the Trinity of the persons or, conversely, that the Trinity of persons does not abolish the unity of the divine essence. There is always the threat of deviation either to the right or to the left and of falling either into the error of Sabellius or that of Arius. [RD 2.288-289]

What is modalism?

The first error Bavinck mentions is Sabellianism, also known as “modalism.” The second title focuses on the essence of the heresy, which teaches that the Father, Son, and Holy Spirit are three successive modes that God has taken on in history. As Bavinck summarizes elsewhere in the same volume, in this heresy, a distinction between the three remains, but it is a distinction in “modes” or “ways of being”, or more accurately, ways of acting. For the three end up being three successive roles that the one God has performed and is performing. The first one, the Father, created the world and interacted with Israel before Christ; the second, the Son, began at the incarnation and lasted until the ascension; the third, the Spirit, continues from that point on to operate in the world as life-giver.

It is not difficult to see the motivation for holding to this teaching: It provides a clearly intelligible model of the Trinity that obviously preserves a strong unity for the Godhead. However, it does so at the cost of trampling over all the biblical teaching affirming the eternal distinction between the Father, Son, and Holy Spirit. That is, all the texts that indicate the three pre-exist creation and do so as distinct from each other, and yet also as the eternal God, are effectively sidelined. By teaching that the three pre-exist creation, too, the scriptures imply that the persons are not products of divine will. In the case of modalism, that is essentially what they are: voluntary styles of behaviour that God voluntarily decided to undertake in relation to his creation. The threeness of God is entirely ad extra (in relation to creation, not something true of God in himself) and temporal.

It is important to make a distinction between this heresy and orthodox accounts of the Trinity that have unfairly been labelled such. I refer here to how Thomas Aquinas and Karl Barth have been maligned on the subject. It is entirely orthodox to say that the Father, Son, and Holy Spirit are three eternal ways of being for the one God. Of course, orthodoxy will also add that the Trinity is nothing but these three, so that we are not to imagine there is a fourth, “bare divinity” alongside them. Rather, the one God eternally exists in three distinct ways. They are not reducible to each other, as if the Father were just eternally wearing Son and Spirit masks. Nor are they reducible to the unity, such that they would really just be illusions.

What is Arianism?

On the other horn of Bavinck’s dilemma is Arianism. As he defines it, “The essence of Arianism is… its assertion that the Father alone and in an absolute sense is the one true God.” [RD 2.290-291] Nevertheless, recent historical work on the theology of Arius has wanted to make further distinctions and qualifications about what the heretic actually taught, as opposed to everything that has been labelled “Arian” throughout history. For this reason, I will rely directly on Lewis Ayres for a summary of his teaching:

“Arius insists that the Father is alone God, simple and immutable. The Son is born from the Father before the creation and although we cannot describe the Son’s birth in temporal categories, we should not say that the Son is coeternal. Such language circumvents the implications of the Son being born from the Father. … For Arius, the three hypostaseis have different levels of glory befitting their different status. … The Son exists because of the Father’s will… . [O]nly the Father is by nature immutable… .” [Nicaea and its Legacy 54-5]

The orthodox rejection of this teaching found one of its most historically determinative expressions in the Niceno-Constantinopolitan Creed, which taught that the Son was “one substance” or consubstantial with the Father, and that he was “not made”. It is important to remember everything that has been said so far when interpreting the former term, homoousion. The pro-Nicene culture (again, to use Ayres’ term) that generated and subsequently defended this Creed did not merely mean that Christ is in the same category as God, as two human beings are. (The term did have this meaning earlier in history, however.) Rather, this term brings with it the doctrine of divine simplicity. The Father and the Son are actually the same ousia, the same being, and what the pro-Nicene theologians called the eternal generation of the Son occurred within this simplicity, not as an effect flowing out of it.

For those following the logic of everything said so far, the meaning of the orthodox doctrine might be obscure. This is not a mistake. What should be clear are the denials it makes: Sabellianism is wrong because it tries to reduce the three to the one as three kinds of temporal activity. Arianism is wrong because it tries to preserve the one by making the Son and Spirit lesser beings, created by the Father. The orthodox doctrine instead affirms that the three persons are eternally distinct, and that they share the same uncreated honour and status because they all exist within the one simple divine being.

Nevertheless, it becomes difficult to understand how this all works. Pro-Nicene theologians do not treat the persons as three divine beings; they nevertheless affirm that each of the three possess all the properties that make God what he is. This makes a clear denial that the persons perform separate psychological functions in the one God, as if, say, the Son were the mind of God and the Spirit the will. They each have life, rationality, will, etc. considered separately. But then, the life, rationality, and will they have is that of the one God, so we cannot say that there are three separate wills here.

In other words, the classic doctrine is intelligible insofar as the doctrines it denies are intelligible; when we turn around to give a positive account of how such a God is, though, the fathers and their successors are quick to point us to the doctrine of divine incomprehensibility. We can never know the Trinity fully, as Gregory of Nazianzus famously expressed:

No sooner do I conceive of the one than I am illumined by the splendor of the three; no sooner do I distinguish them than I am carried back to the one. When I think of anyone of the three I think of him as the whole, and my eyes are filled, and the greater part of what I am thinking escapes me. I cannot grasp the greatness of that one so as to attribute a greater greatness to the rest. When I contemplate the three together, I see but one torch, and cannot divide or measure out the undivided light. [Orations 40.41]

What is monothelitism?

The history of theology proper shows us Christians grappling with the implications of previous conclusions when juxtaposed with new questions. This happened when the church turned from the question of the Son’s relation to the Father to ask: If the Son is truly the one God, how can he also be human?

Chalcedon’s Definition in the fifth century provides the answer to this inquiry, though only by ruling out errors, not by explaining how the truth is possible:

The definition denies Apollinarianism, which said Christ’s divinity took the place of a normal human soul. Rather, it affirms Christ has a complete human nature.

It also for the same reason contradicts Docetism, which taught Christ had no human nature at all.

And it rejects Eutychianism, which stated Christ’s human and divine natures were melded together into a third kind of thing, effectively making Christ neither divine nor human.

Last, it also rules out Nestorianism, conventionally defined to mean that Christ was actually two separate persons, a divine and human, by being clear that Christ was one divine person who assumed a human nature to himself, not two persons working in close concert with each other. (It is disputed whether Nestorius actually held to this view personally.)

These denials are all intelligible; fully explaining the union of Christ in a manner consistent with all of them exceeds the grasp of the human intellect according to patristic and Reformed tradition.

After this Definition was accepted, a subsidiary question arose in the seventh century: How many wills does Christ have? A council at Constantinople concluded that, since Christ had two full natures, he must have two wills. A human nature without a human will would not be complete, and of course God has his one will. Since these natures remain distinct in the incarnation, their natural properties must also be distinct.

Further Resources

For those wanting to study these questions further, the books that have been most useful to me are the following:

James Anderson’s Paradox in Christian Theology , which explains the creedal doctrines, shows how they are apparent contradictions as stated, provides biblical support for them, and then gives an extensive philosophical account for how one can rationally believe a paradox (an apparent but not real contradiction).

Lewis Ayres’ Nicaea and Its Legacy , which shows how the classical doctrine of the Trinity developed. It also undermines narratives about a fundamental opposition between a “Western” view of the Trinity that prioritizes unity versus an “Eastern” view that emphasizes triplicity. Rather, Ayres demonstrates the East and West pro-Nicene thinkers shared a common intellectual culture that had verbally different ways of making the same theological judgments.

Edward Feser’s Scholastic Metaphysics and his Aquinas: A Beginner’s Guide . Feser provides a clear introduction to the basic metaphysical underpinnings of the doctrines of classical theism, and especially how they entail the doctrine of divine simplicity.

James Dolezal’s God Without Parts , which provides an extensive explanation and defense of the doctrine. Also see his article on “Trinity, Simplicity and the Status of God’s Personal Relations” in the International Journal of Systematic Theology. Further, Steven J. Duby’s article, “Divine Simplicity, Divine Freedom, and the Contingency of Creation: Dogmatic Responses to Some Analytic Questions” explains the coherence of the doctrine in relation to its titular issue.

Andrew Fulford is currently studying for a PhD in Reformation history.