1. Introduction: Aquinas’s notion of existence

William Lane Craig has raised several objections to the traditional doctrine of divine simplicity and to the Thomistic account of existence.Footnote ¹ In what follows, we address those criticisms that appear most decisive for his rejection of these doctrines.Footnote ² Before looking at Craig’s criticism, it would do well to summarize Aquinas’s understanding of existence, and how it relates to his articulation of the doctrine of divine simplicity.

To get right to it, then: as Nicholas Wolterstorff has pointed out, the doctrine of divine simplicity cannot be properly understood apart from the constituent ontology from which it ultimately emerges.Footnote ³ This ontology, at minimum, is committed to the idea that existence is something things actually have – or better, participate in – and that it serves as a principle of actuality in things: a principle that actuates the thing itself and whatever properties it has.

Existence, then, at least for Aquinas, is the principle that enables things to exist – the factor that makes them distinguishable from nothing. It is that in virtue of which something is included in reality, having actual presence in the world.

This understanding obviously commits us to the idea that existence is a first-level property (i.e., something attributable to individuals, not merely a second-level property of concepts or propositional functions), amounting to what is sometimes called the thick theory of existence.Footnote ⁵

That statement is hasty. To be more precise, the Thomistic notion of existence is ‘two-sensed’, encompassing both a there-is sense and an actuality sense.Footnote ⁶ (Strictly speaking, even this is somewhat hasty, since – as we’ll see later – there is also a third sense. We will, however, postpone discussion of that for now.)

The there-is sense aligns with Frege’s notion of existence and is used in expressions such as ‘Tigers exist’, which ascribes a property of a property (in this case, the property of being a tiger) and effectively states that the number of tigers – things falling under the concept ‘tiger’ – is at least one, not zero.

So understood, the thick theory of existence does not exclude the thin theory; rather, it resists the reductionist impulse of the thin theory, which claims that existence just is instantiation.Footnote ⁷

This is where the actuality sense comes in. It appears in expressions such as ‘My wife exists’, which seem clearly to denote a property of an individual. Indeed, Thomists (and other proponents of the thick-theory, often enough) insist that this is the deepest and most fundamental understanding of existence – as the principle by which something actually is, and in virtue of which something of that kind can even be numbered. In other words, the reason the number of tigers is not zero is that there is at least one concrete, individual tiger with actual presence and causal power in the world, by virtue of its principle of actuality – namely, its existence.

With respect to his philosophy of God, Aquinas holds that God alone is identical with His own existence, whereas everything else has an essence really distinct from its existence, resulting in a metaphysical composite.Footnote ⁸ This forms the basis for the absolutely ontologically simple God – one who exists entirely in virtue of what He is, whereas everything else exists entirely in virtue of being caused by this single, simple being.

So, that’s how Aquinas – and many other Thomists, Classical Theists, and Neo-Aristotelians – understand existence. Of course, there are plenty of questions and objections one could raise against this view, and many have been raised over the centuries. But for our purposes, hopefully enough is now on the table for us to turn to Craig’s objections and offer replies that we believe to be fruitful in furthering the conversation.

2. Craig’s first complaint

Here’s the first complaint from Craig we’d like to focus on:

Craig continues:

He then quotes William Hasker:

We begin by asking – perhaps with some initial skepticism – whether it is really unintelligible to say that existence exists. And we confidently respond: no, not if one thinks about existence in a certain way.

On this point, Christophe de Ray has conveniently provided a recent article (not referenced by Craig) titled ‘Existence Exists, and It Is God’, in which he offers the following ‘little argument’ to show that existence does, in fact, exist:

1. 1. Existence enables particular things to exist.

2. 2. Existence could not enable particular things to exist unless it itself exists.

3. 3. Therefore, existence exists.Footnote ¹²

At first blush, this seems thoroughly intelligible – at least for someone who subscribes to a thick theory of existence and holds that existence is that in virtue of which something has real presence in reality.

Nevertheless, de Ray immediately acknowledges the very concern Craig raises. He writes:

De Ray then notes that this invites another worry – one that Craig himself does not raise – namely, that in order to explain why there are any beings at all, we seem to be positing yet another being (existence itself), and so the explanation risks circularity.

To avoid this, de Ray ultimately appeals to different modes of existing – a topic that, as we’ll see, connects with Craig’s second complaint. Following work by Vallicella,Footnote ¹⁴ he proposes the Paradigm Theory of Existence (PT):

In short, PT holds that when we say something exists, we’re really saying one of two things: either the thing shares in Existence, or it is Existence itself.

To bring this back around to Craig’s complaint: to say that God exists – which, as Craig rightly notes, translates for the classical theist into something like Existence exists – is certainly not unintelligible, even if it is, let’s admit, ungrammatical. But this is hardly a major issue. We often encounter statements that are thoroughly ungrammatical yet perfectly intelligible (‘Got Milk?’ ‘Man Eats Shark!’ etc.), and we naturally tidy them up, logically speaking, when necessary.

And in the case of God, such an encounter is not unexpected, given the plausible supposition that our language is naturally structured for discussing ordinary, everyday objects – in a word, contingent things that, for Aquinas, are things really distinct from their existence (things that, as it were, share or participate in existence).Footnote ¹⁵

So, of course, if God just is His existence, then to say ‘God exists’ misleadingly suggests that there is both God and His participation in existence – which would make God, essentially, a caused entity. That is obviously wrong. But the apparent oddity, if one insists on being logically precise, can be resolved easily enough by appealing to the notion of a logically simple proposition – that is, a proposition lacking sub-propositional components yet still bearing an assignable truth value – a position defended quite rigorously by Barry Miller.Footnote ¹⁶

This returns us to a point previously postponed: the third sense of existence, which we’ll refer to as the propositional non-predicative sense. By a ‘sense’ here, we mean a distinct logical role or function that the term ‘exists’ can play beyond the senses so far explored. In the uses examined so far, ‘exists’ functions as an incomplete expression – either quantificationally (the there-is sense) or predicatively (the actuality sense). By contrast, in the propositional non-predicative sense it functions as a complete expression, one that does not require supplementation by a distinct subject.Footnote ¹⁷

In other words, its simplicity consists in the fact that it accomplishes, in a single, non-decomposable act, what logically complex propositions achieve through distinct parts – namely, the joint exercise of referential and predicative functions.Footnote ¹⁸ Moreover, in this case, what is ‘predicated’ is not something general that could apply to many subjects, but something wholly peculiar – indeed, identical – to its referent. Thus, the propositional sense preserves the role of signifying actuality while dispensing with the subject–predicate structure that presupposes ontological composition.

This allows us to avoid the clumsy and misleading formulation that ‘existence exists’, which seems to predicate existence of existence. That, however, is not how Existence itself should be understood. One might try, very loosely, to render the claim as ‘necessarily, one and only one thing exists’, but even this is misleading, since it reverts to the predicative (actuality) sense by appearing to attribute existence to a subject.

What is required, then, is precisely the propositional non-predicative sense. Quite plausibly, Existence – or better, we think, Exists! – accomplishes this.

Thus, ‘God exists’ (or even ‘Existence exists’) is simply an ungrammatical way of expressing something like ‘Exists!’ And it makes perfect sense that any attempted logical analysis of an absolutely simple being would feel peculiar, since such a being is not – and cannot be – a subject bearing really distinct non-relational properties (which would amount to ontological complexity, and presumably, a basis for propositional complexity).Footnote ¹⁹ This may sound odd at first, but it is far less so once we recognize the traditional – and, we think, undeniable – point that when things differ in kind, the terms applied to them must shift accordingly. Hence the need for two different, though related, senses (as discussed in the next section). Given that God is wholly unlike the world He creates, we should expect our language about God to be somewhat unusual. What would be surprising is if our God-talk sounded entirely familiar, for that would all but guarantee an anthropomorphic distortion.

Thus far, we believe we have adequately met Hasker’s challenge (endorsed by Craig) to ‘produce a clear and intelligible statement of what those formulas intend’, while in no way conceding that ‘if taken at face value, they do not and cannot express truths’.

Let us now turn to the second objection, since it directly relates to a move appealed to in our response to the first.

3. Craig’s second complaint

Here is Craig’s second complaint:

As we analyze his complaint, there are two aspects worth addressing.

First, Craig is attacking a straw man – plain and simple. No Thomist, and certainly not Aquinas, thinks existence ‘comes in degrees’ in the sense that something can half-exist or partially exist.Footnote ²¹ Rather, the appeal is not just to (1) modes of being (which Craig acknowledges) but also to (2) a possible conceptual ordering of those modes according to their ontological richness.

Once one follows Aquinas (as Miller does) in holding that a contingent thing’s act of existence is a bounded instance of existence – bounded by its finite essence – it becomes quite reasonable to allow that some things can be more or less ontologically rich.Footnote ²² Their essence may constrict existence more or less, yielding a higher or lower mode of being. This is not to claim that such an ordering is easy to map out in every case; only that it is intelligible and frankly quite plausible. While we can acknowledge difficult or borderline cases, it hardly seems controversial that a human being enjoys a higher, more excellent mode of existence – a richer participation in being – than, say, an amoeba. (Indeed, in Craig’s own use of Michael Murray’s theodicy regarding animal suffering in his debate with Stephen Law, he appeals to the limited capacities of lower animals – for example, their lack of a first-person perspective – which constrains both their participation in the moral community and the moral significance of the negative stimuli they might endure.)Footnote ²³

Miller makes the point nicely when he says:

So, rather than defending the traditional ‘full-throated’ doctrine of analogy – and thereby inviting objections unnecessary for our purposes – we can meet Craig on categories he already grants.Footnote ²⁵ To assist in our response, we turn now to a notion originally brought into the literature by Miller and applied quite fruitfully to God-talk and to different modes of being: the notion of a limit-case instance of something.Footnote ²⁶

Simply stated, a limit case can be contrasted with what Miller calls a limit simpliciter. The fundamental difference is this: a limit simpliciter – for example, the speed of light – is still a member of an ordered series (in this case, speeds). A limit case, by contrast – such as a standstill – is not itself a member of that series but rather what the series converges toward. Classic illustrations include polygons with an increasing number of sides converging on a circle – the ‘limit-case polygon’, though of course a circle is not a polygon – or a line of ever-decreasing length converging on a point.

Ultimately, Miller contends that such a conceivable ordering points toward a limit-case instance of existence – more precisely, a zero-bounding instance of existence. That is, an ordering of instances of existence according to various bounds is ordered, for Miller, toward an instance of existence which is really not an individual at all, because it is bound by nothing. It is, rather, entirely unbounded – unrestricted. And that, of course, is what Miller says God is: the zero-bound instance of existence.

Now, while the limit-case instance of an ordered series is not itself a member of that series, it must still bear some real similarity to the members; otherwise, we could just as easily say that a series of decreasing speeds converges upon a circle – which is absurd. The series converges upon a standstill. The non-interchangeability of limit-case instances within ordered series thus requires both real similarity and real difference – which is precisely the metaphysical ground for the sort of analogical predication Thomists employ in God-talk.

In fact, Miller himself distinguishes two genuinely irreducible kinds of similarity relations:

1. 1. that in which certain things share a property in common; and

2. 2. that in which the members of an ordered series stand in relation to their respective limit case.

The relation between God and the world is like (2). While God bears a real similarity to creation, it is similarity-in-radical-difference, for God is not a creature at all but exists in an entirely different mode altogether – precisely what the limit-case illustrations help render plausible.Footnote ²⁷

Thus, we see that one could, in principle, bypass the long-standing controversies of analogy altogether and instead speak only of modes of existing and of the natural shift in the sense of a term when applied across things that differ in kind. (Would anyone deny this?) Moreover, it makes perfect sense to say that something exists either in a creaturely mode – by participation – or in the divine mode – by identity – and that, ultimately, is all that is required to dissolve the difficulties Craig raises. It just so happens that we find Miller’s notion of God as the limit-case instance of existence particularly instructive on this score.

4. Conclusion so far

We have examined two of Craig’s complaints against Aquinas’s understanding of existence as it ultimately relates to his philosophy of God, and to the doctrine of divine simplicity in particular. We have found that Craig’s objections are hardly forceful – that good sense can be made of the notion of existence itself existing, and that sense can also be made of existence ‘coming in degrees’, so long as one understands this in terms of conceptually orderable modes. Moreover, once one grasps the idea of modes of existence, this provides a sturdy basis for understanding how existence itself exists, since two such modes are as follows: existence can be either in a creaturely mode (as participated or shared in – and bounded, as it were) or as Existence itself (unbounded), as the paradigm theory proposes.

While Craig has raised numerous challenges to the doctrine of divine simplicity, we hope to have shown that these two are an entirely inadequate basis for rejecting it.

5. A challenge for Craig

Having addressed two of Craig’s objections, we now raise a friendly challenge of our own.

Craig rejects the Thomistic account of divine simplicity and the thick theory of existence that supports it. Yet, once granted, this metaphysical picture yields substantial theoretical benefits: it secures God’s existence, His aseity, His radical uniqueness, and thus His ultimacy.

Briefly, here is why.

In a broadly Thomistic setting, the question How can it be that something exists? arises only for what does not exist by its very nature – that is, for what is really distinct from its act of existence. But the fundamental first cause – reached, let us assume, through cosmological reasoning – is not distinct from its existence. It is the paradigm, the limit-case instance, of existence itself. For such a reality, the explanatory demand is misplaced: its explanation is internal, not derivative.

Thus, God’s existence is not a ‘brute fact’. If a being is identical with its existence, we gain an essentialist explanation both for why it exists and for why it must exist. Its nature simply is: Exists!Footnote ²⁸

To clarify, we contend that Exists! is both like and unlike an analytic proposition.Footnote ²⁹ Analytic propositions have truth grounded in internal affirmation (the predicate contained in the subject) and falsity ruled out by internal contradiction. By contrast, Exists! is unlike an analytic proposition because, absent complexity, its truth cannot be determined by any internal structure – since, by its nature, it has no such structure. In other words, this could not form the basis for any sort of ontological argument; it is not something one could know to be true simply by studying the proposition itself.

However, that does not mean we cannot come to know that it is true through external evidence – most relevantly, through cosmological or existential reasoning of the sort Aquinas proposes (which we have no intention of defending here).Footnote ³⁰ Once that is appreciated, what initially looked like a hindrance – namely, the lack of internal structure – turns out to be an impenetrable safeguard in another sense: internal negation is equally impossible. If we know it to be true, we cannot possibly discover it to be false. In this respect, it behaves like an analytic truth: external evidence yields its truth, but its necessity is grounded internally.

And here lies the dialectical payoff. This immediately nullifies the question ‘Why does God exist?’ – in exactly the same way that, once one understands what a mountain is, the question ‘Why do mountains have valleys?’ no longer gets a grip. God’s existence, given His nature (Exists!), is genuinely self-explanatory.Footnote ³¹

Next, we can also see how such a being terminates any collection or ordered series of caused entities that are really distinct from their existence, and why there can be only one such being – by the usual per se causal reasoning of Aquinas. For all things that share in, or participate in, some perfection – in this case, existence – must find their ultimate explanation in that which has that perfection essentially, which is God, or the paradigm existent. Otherwise, one never secures an adequate explanation for how such a perfection (or property) could have entered into a system of beings whose natures are really distinct from their existence – that is, contingent beings.

The conclusion of the radical or ‘uniquely unique’ nature of this fundamental entity can be reached in two ways within the Thomistic system. The first is by asking whether there could be more than one limit-case instance of existence. But there could not be, since what marks some entity as the limit-case instance of existence is precisely the absence of any bound, whereas what makes something an individual is precisely the presence of some bound. This is why we (along with Miller) contend that the limit-case instance of existence is not an individual (a concrete entity, yes, but not an individual in the proper sense). Simply put, to insist upon the possibility of there being two instances of the limit-case instance of existence is self-contradictory, since for there to be two distinct instances would logically require that they be individuated – which is to posit exactly that which cannot possibly be said of the limit-case instance of existence. So, if there is one, there is only one.

The second approach proceeds from the notion of simplicity itself. Here is perhaps the most straightforward way to make the point: recall that whatever is identical to its existence must be altogether simple (its essence just is its existence). Now suppose that there are two distinct instances of that whose essence just is its existence. Since both are subsistent existence itself, they share at least that feature in common. However, since these entities are really distinct from one another, each must have at least one feature or property that the other lacks. But whatever that distinguishing feature is must be compounded (admixed) with what they share in common – and this contradicts the very notion of simplicity.Footnote ³²

In other words, assume there are two beings that are the paradigm existent – pure existence, absolutely simple being. If there are two really distinct entities, then, trivially, there must be some difference between them, even if that difference is indiscernible. Whatever that distinguishing feature is would have to be really (not merely conceptually) distinct from the essence of the being, or from that which makes it to be the absolutely simple being that it is. In that case, we would no longer have something absolutely simple but rather a metaphysical composite of some quality or feature and that which grounds it as distinct from that feature. Thus, a being whose essence just is its existence – absolutely simple being – is necessarily unique.

These are, we take it, welcome results for any theist: namely, that such a metaphysical account provides the resources (1) to avoid treating God as a brute fact, (2) to make intelligible the claim that God exists necessarily and is truly self-sufficient and a se, (3) to secure an in-principle – rather than merely happenstance – monotheism, and (4) to provide a clean conceptual basis for why the contingent order must terminate – explanatorily and necessarily – in this very being.

We are now ready to state our challenge to Craig. Given his rejection of the metaphysical commitments that yield these fruitful results, does he have adequate resources of his own to reach them? More specifically, can he ultimately ground not just God’s existence but God’s necessary existence – explain how God (and God alone) can and must terminate an ordered series or collection of contingent things, how there is in principle just one fundamental first cause – and, for all of this, how the resources he sets out are not easily co-opted by a naturalist? That is, can he achieve principled results on these questions that do not invite easy parity responses from nontheists? We are skeptical that he does – at least not for all of them.

Let us now indicate why.

Take first the case of God’s necessary existence. Craig is, at best, ambivalent about whether existence itself is a property, yet he still wants to insist that necessity of existence is.Footnote ³³ At this point, Craig typically appeals to Anselm’s conception of God as ‘a being than which none greater can be conceived’, taking this to imply necessary existence, since a being that could fail to exist would be less great than one that could not.Footnote ³⁴ All well and good – but this doesn’t actually explain how a being could have necessary existence or whether any other beings could. And those, surely, are the really important questions. (Notice, for classical theists, God’s perfection is downstream from – and explained by – divine simplicity. Perfect traditionally just meant ‘thoroughly made’ or ‘complete’. God is perfect insofar as He is purely actual, with no potentials left to actualize in order to further His perfection as the kind of thing He is, nor any deprivations. Not only that, but divine simplicity also helps to differentiate between relative and absolute perfection – another area where Craig’s resources may be lacking. For whereas all finite things are perfect according to their sortal kind to the extent that they more fully realize it, God is unrestricted by any finite essence and thus is a being possessed only of purely positive properties – or, more precisely, the limit-case instances of those properties.)Footnote ³⁵

Assuming Craig does not intend to rely on the ontological argument as straightforwardly sound, his notion of necessary existence seems merely stipulative.Footnote ³⁶ What’s missing is an account – a metaphysical story – of how such necessity attaches, as it were, to God. For Craig, God is neither identical to His existence nor to His necessity of existence. So what grounds this necessity?Footnote ³⁷ If nothing does, then it appears to be brute. And brute necessary existence is, to borrow Craig’s own language, ‘worse than magic’, for in magic there is at least the presumption of an explanation.Footnote ³⁸

Surely, then, simply declaring that something exists necessarily does nothing to dissolve the relevant mystery; if anything, it compounds it! In fact, the entire suggestion seems nonsensical: if something is brute, there is literally no rhyme or reason behind it. But how could something be a brute necessary existent? If anything calls out for explanation, it is not just why something exists, but why it could not fail to exist. And if that fact is brute – if there is no explanation whatsoever – then how could we reasonably say, or claim to know, that it exists no matter what and won’t simply, brutely, wink out of existence? The very idea of ‘no rhyme or reason’ undermines the possibility of giving such an account at all.

Imagine someone says that there is some manatee – and that this manatee has brute necessary existence. Could anyone really find it within themselves to accept such a position? We take it they could not, presumably because they would intuit that there’s nothing about being brute that could secure something so radical as necessity. Again, the very notion of being brute seems to decidedly cut against the idea altogether. And what is said about the manatee, we think, could and should be said about anything else, since differences in size, shape, or location make no relevant difference here. In all honesty, brute contingency is already costly enough, but the notion of brute necessity seems even more untenable.

Again, it will not do simply to insist that God would not be maximally great if He lacked necessary existence. While some may deny that necessary existence is a great-making feature, the authors of this article do not. We simply insist that this is not an explanation – of course it isn’t. What we need is an account of how something could have necessary existence. Theists already agree that God, if God exists, is maximally great; that is not the dispute. The dispute is whether Craig’s conception of God can make metaphysical sense of such an entity, and here we contend that his model seems unable to do so.

Moreover, even if we grant to Craig that his conception of God somehow includes necessary existence, why couldn’t something else possess it as well? What makes this so-called ‘great-making’ property exclusive to God? The classical theist has a clear and principled answer: only God (Exists!) is identical with His existence – because only God (Exists!) can be.

Craig, by contrast, seems to have no comparable resources in his metaphysical toolkit to explain this exclusivity; no metaphysical barrier he can erect, in other words.Footnote ³⁹ This means that even if one grants that God (brutely) exists necessarily, this neither excludes the possibility of other entities existing necessarily and grounding the contingent order – or certain parts of it – thus undermining divine ultimacy and aseity.

Moreover, if God’s necessary existence is brute, what advantage does Craig really have over the atheist who, acknowledging the same need for a necessary foundation, simply declares that the fundamental physical reality – say, the initial singularity or quantum vacuum – exists necessarily? The parity is perfect: if God ‘just exists necessarily’ without further explanation, then why not the universe? After all, the atheist could just as easily – following Graham Oppy – stipulate that necessary existence is contained within the real definition of whatever fundamental physical entity he posits.Footnote ⁴⁰ Craig, after all, provides no deeper metaphysical story of how necessity attaches to God beyond mere definitional stipulation.

Now, to be clear, we do think the concept of God entails necessary existence; we just don’t think this can be coherently or consistently cashed out within Craig’s wider commitments (especially given the metaphysical distinctions he rejects) without doing so in a way that either (a) licenses the atheist to make the same sorts of moves, or (b) leaves his account entirely empty – brute – or, as we suspect, (c) both.

And to reiterate: this parity poses no threat to classical theism. Internal to classical theism, there is one thing – and just one thing – that can include existence as part of its essence, and in that case must be identical to it (so, not really a ‘part’ at all).Footnote ⁴¹ Thus, nothing else could have or include necessary existence as a feature or property.

To be sure, Craig does attempt to appeal to God’s being broadly logically necessary through possible-worlds semantics:

But there are major problems here.

First, this is surely not an explanation of God’s necessary existence but, at best, a mere description that is semantically equivalent, especially if one adopts a metaphysically neutral understanding of possible worlds.

Second, if one were to insist that it were somehow explanatory, it would carry the utterly bizarre implication that God’s existence depends on the modal landscape – that God’s being is owed to certain facts about possibility, as though God’s necessity is secured by surveying the descriptions one finds in each of the infinite possible worlds.Footnote ⁴³ (Classical theists strongly deny this: the modal landscape is set and delimited by God’s power and goodness; all possibility is ultimately grounded in actuality – namely, God’s.)

Ultimately, we are skeptical that Craig can offer satisfying resolutions to these issues within his own metaphysical paradigm. While he undoubtedly wishes to affirm many of the same things classical theists say – that God is the ultimate (and only) first cause of the contingent order and the sole being that exists by the necessity of His own nature – we contend that he almost certainly renders those responses either impossible or significantly weakens them (to the point of being adoptable by naturalists) by rejecting so many of the core commitments that motivate classical theism and ground traditional divine simplicity, particularly the claim that God just is His existence.

These difficulties are made possible – and compounded – by Craig’s broader metaphysical commitments, particularly by what he rejects. For instance, he is a professed property anti-realist and denies both constituent and relational ontology.Footnote ⁴⁴ This is noteworthy, and perhaps revealing: the very reason his account proves so vulnerable to atheistic parity responses may be that his wider metaphysical outlook so closely mirrors theirs.