Ryan Mullins provides an admirably clear and direct statement of the most important objections to the doctrine of divine simplicity. But the objections fail, and Mullins fails to consider the dire implications of rejecting the doctrine.

Take the latter point first. Though its critics often treat the notion of divine simplicity as an unimportant curiosity, there are good reasons why the Church Fathers, the medieval Doctors, and two ecclesiastical councils regarded it as essential to orthodoxy. For one thing, it is a consequence of God’s ultimacy. For anything composed of parts is ontologically posterior to those parts, and can exist only if something causes the parts to be combined. Hence if God were composed of parts, there would have to be something ontologically prior to him and something which combines those parts, thereby causing him to exist. But there is nothing ontologically prior to or more ultimate than God, and nothing that causes him. To be the uncaused cause of everything other than himself is just part of what it is to be God. Hence God cannot be composed of parts but must be absolutely simple.[1]

For another thing, divine simplicity safeguards God’s uniqueness. Where there is a distinction between a thing and its nature or essence, then that thing will not necessarily be unique. For example, there is a distinction between a given particular triangle and triangularity as a common nature or essence. Given that distinction, something other than that particular triangle might share that same nature or essence, so that there can be more than one triangle. By contrast, according to the doctrine of divine simplicity, there is no distinction between God and his nature or essence. God just is his nature, so that it is not something that he could have in common with another thing. And if there cannot be anything else that has the divine nature, then there cannot even in principle be more than one God. In this way and others, divine simplicity protects monotheism.[2]

These are the reasons why defenders of divine simplicity sometimes go so far as to argue that to deny the doctrine entails atheism. For if being an uncaused cause and being absolutely unique entail simplicity, then to deny that there is anything that is simple or non-composite is implicitly to deny that there is an absolutely unique uncaused cause. And since to be God just is to be an absolutely unique uncaused cause, to deny divine simplicity is therefore implicitly to deny the existence of God.

The stakes in this debate are therefore much higher than Mullins lets on, and for a theist to refute the doctrine of divine simplicity would require more than merely raising objections of the kind Mullins does. It would require explaining how such objections could avoid inadvertently refuting theism itself.

In any event, Mullins’ objections, I have claimed, do not succeed. Consider first the claim that divine simplicity is incompatible with divine freedom. The objection begins by noting that the doctrine of divine simplicity holds that God is identical with his attributes. God doesn’t merely have omnipotence but rather is his omnipotence; he doesn’t merely have omniscience but is his omniscience; and so on. But what is true of God’s attributes is true of his acts as well. God just is his act of creating the world, for example. Now, since God exists necessarily, it follows that if God just is his omnipotence, then his omnipotence exists necessarily. But the same thing would have to be true of his acts, such as his act of creating the world. That act would exist necessarily as well.

But in that case, the objection concludes, we have the result that the world exists of necessity. And that is problematic in two ways. First, it seems obviously false, because though the world does in fact exist, it is hard to doubt that it could in principle have failed to exist. Second, the result seems to entail that God does not act freely. He had to create the world. But that is contrary to standard Christian doctrine, which holds that God freely created the world insofar as he could have opted instead not to create it. Similarly, it is Christian doctrine that God could have refrained from imparting grace to us, and this too is incompatible with the result that God’s acts are as necessary as he is.

Now, one way to see what is wrong with this objection is in terms of a distinction drawn by the Thomist philosopher Barry Miller.[3] Suppose Socrates grows a beard. That involves the acquisition by Socrates of a real property. But suppose Socrates becomes shorter than Plato, not because of any change in Socrates himself, but rather only because Plato has grown taller. That involves the acquisition by Socrates of a mere “Cambridge property” rather than a real property. The real change, and thus the acquisition of a real property, is in Plato rather than in Socrates.[4]

Now, what the doctrine of divine simplicity claims – contrary to what Mullins supposes (in what he labels premise (9) of his argument) – is, not that all of God’s properties are identical and thus are as necessary as he is, but rather that all of his real properties are. He can have Cambridge properties that are merely contingent. And his having created the world is among these contingent Cambridge properties. That the world comes into being does not entail the acquisition of a real property by God, any more than Socrates’s becoming shorter than Plato by virtue of Plato’s becoming taller entails the acquisition of a real property by Socrates. When we keep this distinction in mind, we can see that divine simplicity does not have the implication that the creation of the world was necessary, and thus does not have the implication that God is not free.[v]

(Mullins says that his argument establishes three problems for divine simplicity, concerning “God’s freedom, grace, and necessary existence.” But the objection concerning grace is just a special case of the objection concerning freedom, since the alleged problem for simplicity derives from the fact that grace is given by God freely. And the objection concerning freedom in turn rests on the objection concerning God’s necessity. So Mullins’ critique really boils down to the latter objection, which gets off the ground only if one ignores the distinction between real and Cambridge properties and wrongly supposes that the doctrine of divine simplicity claims that all of God’s properties are identical and thus equally necessary. Once that distinction is made, Mullins’ entire critique collapses.)

Mullins also accuses advocates of divine simplicity of making “cheap” appeals to mystery in defending the doctrine, and in particular of resorting to “mysterious language” in explicating it. But his attack is aimed at a caricature, and he misses the point about language that the defender of divine simplicity is trying to make.

Here is the basic idea. Aquinas notes that there are three basic ways in which we use terms.[vi] The first is univocally or in the same sense, as when we speak of a baseball bat and a cricket bat. “Bat” has exactly the same meaning in each case, even though the one kind of bat is slightly different from the other kind. The second way we use terms is equivocally or in completely unrelated senses, as when we speak of a baseball bat and the sort of bat that flies around in your attic. The meanings we attach to the word “bat” in these two cases are in no way related. The third sort of usage, the analogical use of terms, is intermediate between univocal and equivocal uses. Consider the way that we might speak of good food, or of a good book, or of a good person. “Good” doesn’t have exactly the same meaning in each case, because the goodness of a meal is a very different sort of thing from the goodness of a book, and both are very different in turn from the goodness of a person. But the meanings are not entirely unrelated either. Aquinas holds that what we are saying is that there is something in a good book or in good food that is analogous to what is in a good person, even if it is not the same thing (as it would be if the terms were being used univocally). We are expanding the sense of the term when we apply it to things so diverse, even though we are not completely severing the semantic connection (as we are in the case of equivocal usage). And note that we are still speaking literally in each case. To call a book, or food, or a person good is not to speak metaphorically. Univocal language is not the only literal kind of language.

Now, there is nothing at all “mysterious” about analogical usage. On the contrary, it is an extremely familiar feature of ordinary language. Moreover, it is a kind of usage that is unavoidable when we try to describe things that are remote from everyday experience – as we do, for example, in physics. Consider general relativity, which describes the structure of time and space at the largest scale, and quantum mechanics, which describes the structure of matter at the smallest scale. Here we have to find some way to talk about physical realities that are very unlike the kind of physical things with which we deal in everyday life, which is the context in which our terms for physical things have their natural home. Hence we have to rely very heavily on analogy.

So, for example, general relativity speaks of “curved space.” This is very odd, when you think about it. The way we ordinarily use the term “curved” is to apply it to the shapes of the things that occupy space. For example, we speak of the curvature of the surface of a ball, which you would observe as you held it up before your eyes. Relativity requires us to apply the concept to the space through which the ball and other objects move, and this is a kind of curvature you cannot observe. Quantum mechanics requires us to speak of certain entities as exhibiting both particle-like and wave-like properties. This too is very odd. Being a “particle” in the usual sense of the term rules out being a “wave” in the usual sense, and vice versa.

Now, there is nothing wrong with this usage. There are solid theoretical reasons why we simply cannot describe what we are trying to describe without using terms like these. But we have to stretch the terms considerably, to the extent that we are not using them in exactly the same way they are used in ordinary contexts, even if we are not using them in completely unrelated ways either. We are using them in an analogical way. Because we have to stretch the meaning so far, the usage is somewhat mysterious. But there is no “cheap” mystery here, because the theoretical reasons that have pushed us in the direction of stretching language in this way have paid for this usage, as it were.

Now, the defender of the doctrine of divine simplicity holds that this is exactly the sort of thing that is going on when we speak of God. When we reason to the existence of an uncaused first cause, we are pushing explanation to its outermost limits. Indeed, we have to stretch language even further than the physicist does, because we are applying it to something that is altogether beyond time, space, and matter. We find that such a cause cannot serve as an ultimate explanation unless it is not limited in any of the ways that temporal, spatial, and material things are, unless it exists in an absolutely necessary rather than contingent way, and so on. Accordingly, it must be radically unlike the things to which we ordinarily apply terms like “cause.” And one of the ways it must be radically unlike them is in being simple or non-composite, because composite things requires causes of their own and therefore cannot be first or ultimate causes.

Of course, atheists will disagree with all this, but that is not to the present point. The point is that theistic explanation – which Mullins himself presumably accepts – already requires pushing language far beyond its ordinary usage, independently of considerations about the doctrine of divine simplicity. It is unfair, then, for Mullins to accuse defenders of the doctrine of making “cheap” appeals to mystery, as if they were guilty of an arbitrary or ad hoc move. The very logic of theistic explanation, the defender holds, makes both divine simplicity and the stretching of ordinary linguistic usage simply irresistible.[vii]

Edward Feser is Professor of Philosophy at Pasadena City College in Pasadena, California. His many books include Five Proofs of the Existence of God (Ignatius Press, 2017) and Aquinas (Oneworld Publications, 2009). More information can be found at his webpage and blog.



[1] Cf. Thomas Aquinas, Summa Theologiae I.3.7.

[2] Cf. Thomas Aquinas, Summa Theologiae I.11.3.

[3] Barry Miller, A Most Unlikely God (University of Notre Dame Press, 1996), pp. 106-12. Cf. Thomas Aquinas, Summa Theologiae I.13.7.

[4] The label “Cambridge property” reflects the special interest taken in this notion by Cambridge philosophers like Bertrand Russell and J. M. E. McTaggart.

[v] For a related recent response to this objection to divine simplicity, see Christopher M. P. Tomaszewski, “Collapsing the Modal Collapse Argument: On an Invalid Argument Against Divine Simplicity,” Analysis 79 (2019): 275-84.

[vi] Cf. Summa Theologiae I.13.5.

[vii] I defend divine simplicity at greater length in Five Proofs of the Existence of God (Ignatius Pres, 2017), in chapter 2 and at pp. 189-96 and 225-26.