This doctrine [divine simplicity] 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.

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.

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