In defence of qua-Christology

Abstract

Recent analytic theology has seen a wave of excellent work on the fundamental problem of Christology, the question of how one and the same person can be human full stop and divine full stop. Along the way, new objections have been raised for a venerable family of Christological views, whose distinctive is the employment of qua-devices to dissolve the difficulties stemming from the dual nature doctrine of Chalcedon and its successors. My objective in this article is twofold. First, I propose to lay out a hierarchy of principles that should guide the search for a Christological theory. I then use these principles to illuminate the best qua-theoretic approach to Christology. Finally, I argue that the best qua-theory is at worst on a par with major recent views.

Introduction

Recent analytic theology has seen a wave of excellent work on the fundamental problem of Christology, the question of how one and the same person can be human full stop and divine full stop. Richard Swinburne has defended a ‘split mind’ theory.¹ Tim Pawl has put forward his ‘conciliar’ theory,² and Jc Beall has made a case for true contradiction.³ En route, each has raised issues for a more venerable approach to Christology, the family of views whose distinctive is the use of qua-devices to dissipate the fundamental problem.

My objective in this essay is twofold. First, I propose to lay out a hierarchy of principles that should guide the search for a Christological theory. I then use these principles to illuminate the best qua-theoretic approach to Christology. Finally, I argue that the best qua-theory is at worst on a par with the other proposals and so one of the better candidates for truth.

The fundamental problem of Christology

The doctrine of the incarnation, in a slogan, says that the second person of the Trinity (hereafter: God the Son) united with a human nature (hereafter: Jesus of Nazareth) constitutes one person, Christ, the redeemer. Orthodoxy⁴ insists that Christ is fully divine. Orthodoxy insists that Christ is fully human. Orthodoxy insists that Christ is thoroughgoing unity; the communicatio idiomatum demands that Christ have all of the attributes of God the Son as well as all of the attributes of Jesus of Nazareth. Orthodoxy's insistences get it into trouble.

Richard Cross (2011) sets out the Fundamental Problem of Christology as follows:

1. 1. Christ is divine, full stop.

2. 2. Christ is human, full stop.

3. 3. Some properties necessary for divinity full stop seem to be incompatible with some properties necessary for humanity full stop.

We can, in fact, turn the observations in (1)–(3) into a contradiction by choosing a pair of properties, one necessary to divinity, one necessary to humanity, that seem incompatible. Because there are many such pairs, there are many looming contradictions for orthodoxy. For specificity we will focus on one pair, but we should not forget that any good strategy for dealing with the fundamental problem ought to be fully general (e.g. the discovery that one pair of seemingly opposed attributes are compatible because of some quirk of the concepts involved in their formation is not a solution to the fundamental problem, unless it is paired with a particularist strategy that finds a saving quirk in every pair).⁵

1. 1. God the Son is immutable.

2. 2. Jesus of Nazareth is mutable.

3. 3. Any attribute of God the Son is an attribute of Christ.

4. 4. Any attribute of Jesus of Nazareth is an attribute of Christ.

5. 5. Christ is immutable.

6. 6. Christ is mutable. ⊥

Because (1)–(4) are insistences of orthodoxy, the space of options in addressing the fundamental problem is fairly limited. One option, recently defended by Beall (2021), embraces the contradiction and works to show that it's not so bad as you might have thought, using subclassical logic and a sophisticated philosophy about the relationship between formal logic and theory-building within a field of inquiry.⁶ The only other option is to deny that (5) and (6) lead to a contradiction. Any way of denying the inferences from (1) and (3) to (5) or from (2) and (4) to (6) will undermine the theological role of the communicatio idiomatum – to secure the unity of Christ as well as full stop divinity and humanity.

Any way of denying that (5) and (6) can't both be true will be weird. But if words mean what, before we encountered this problem, we took them to mean, and if logic behaves the way we took it to behave, and if language works in theological contexts more or less the way it works in non-theological contexts, and if all of the pieces of our Christological theology are going to do the jobs they were insisted upon to do, then we're stuck with a contradiction. The better a solution to the fundamental problem, the better it contains and conceals its weirdness.

The literature on the fundamental problem consists in positive and negative phases. In positive phases, it develops views about how to undermine the contradiction between sentences like (5) and (6). In negative phases, it looks to expose the weirdness of rival ways of undermining that contradiction. We can distil these types of weirdness into a series of principles, which collectively allow us to test Christological views and see what strange things they ask us to do. Without further ado, we will state the principles, with a brief note on their motivation.

principle of theological conservation: We should not solve the fundamental problem by abandoning orthodoxy, or by undermining the ability of orthodoxy's insistences to secure the unity, full stop humanity, and full stop divinity of Christ.⁷

principle of semantic conservation: We should not solve the fundamental problem by giving key terms meanings inconsistent with those we pretheoretically would have given them without adequate linguistic evidence.⁸

principle of semantic continuity: Meaning should be governed by the same rules in Christological contexts as it is in non-Christological contexts.⁹

principle of logical conservation: The logic governing Christological theories should be the same as that governing other theories.¹⁰

principle of transparency: We should not posit hidden structure in language or in the world to solve the fundamental problem.

Of course, we know that every view will violate one or more of these principles, to some extent or other. The determining questions are: how much, and how badly? Not all of these principles are created equal. The hierarchy I will suggest is roughly meant to reflect the strength of the arguments in favour of each.

the principle of theological conservation is of paramount importance; violating it is enough to refute a view, since this entire inquiry is an exercise in theological conservation. This is not because I take myself to be in possession of decisive reasons to prefer orthodox to heretical Christologies. I'm not. But the inquiry into the fundamental problem is at heart an exercise in theological conservation. If heresy is on the table, inquiry ends too easily. We can dispense with either of Christ's natures, or with the communicatio idiomatum, and be done with it. The difficult question is whether the fundamental problem has an orthodox solution. Heretics should welcome this inquiry, because an orthodox solution provides them with a foil against which to compare their views. The problem with heretics in this context is not that they must be wrong, but that they are cheating.

Next in importance are the principles of semantic conservation and continuity. We only have a fundamental problem because we take ourselves to have some reasonable pretheoretical grasp of what terms like ‘mutable’ and ‘immutable’ mean, and use them to characterize divinity and humanity partly for that reason. There's a content that we think is the case and is expressed by those particular words. Violations of semantic conservation chip away at the motivation for saying what properties a divine or human being must have in the first place by replacing that original content with something different. This does dissolve the problem, but for the price of saying very little about what a divine or human being is. Like going heretical, they undermine a premise of the inquiry.

Violations of semantic continuity have a similar effect, separating the rules for how terms gain their meaning into Christological and non-Christological parts. But we only use these terms in Christological contexts because we take ourselves to know what they would mean based on our (perhaps implicit) knowledge of the rules of the language. We once again have a weirdness that is corrosive to the premise of our inquiry. In addition, semantic continuity violations will tend to be ad hoc.

To illustrate these two principles in action and further motivate their importance, consider an extreme violation of semantic conservation. Suppose a Christological theorist proposed that we take ‘mutable’ to be synonymous with ‘is an ocean’ and ‘immutable’ to be synonymous with ‘is not a sand dune’. Applied systematically, this would solve the fundamental problem. But it would be a terrible solution. Why? Because that is not what those words mean. The theorist has not solved the problem but changed the subject. They have violated semantic conservation. This undermines the inquiry.

So suppose our theorist comes back: these special meanings only apply in Christological contexts. The words ‘mutable’ and ‘immutable’ mean what you always thought they meant outside Christological contexts. But there's something special about Christology that triggers different rules for what meanings words take on. Now we have at least tipped our cap to semantic conservation. But the theorist's move is ad hoc. It is a case of special pleading. Why? They have violated semantic continuity. This undermines the inquiry.

Of course, this is not to say that sometimes we don't learn that words mean something other than we expected, or that some contexts don't sometimes create special meanings. But these must be defended by normal linguistic evidence, as the principles require. Most realistic theories will not be as absurd as the examples used here. But they face the same problem. The difference is one of degree.

An aside. Purveyors of Apophatic theology, the via negativa, may cry foul at the importance placed on principles of semantic conservation and continuity. Theological language, they claim, does not work like ordinary language. It should not be continuous with, or consistent with, the meanings of words in ordinary contexts. It's worth noting in response that these principles are only meant to be prima facie desirable; everyone will run afoul of one or more of them. Their presence allows us to give structure to the discourse, and to see exactly which trade-offs one view makes against another. Someone with an apophatic solution to the problem will have to argue that their solution makes better trade-offs than its rivals. The specific ordering I give here reflects my own judgments, but is not meant to be dispositive.

But things may not even be so bad. While Apophaticists are certainly welcome to postulate polysemy or revisionary semantics, the core insights of the view do not require either, and so place on those crying foul a burden of argumentation that must be discharged. The Apophatic slogan says that there are no true positive predications about God. The best we can do is say what God is not. The slogan does not seem to require semantic discontinuity or revision. ‘God is good’ is a positive predication. It comes out false. ‘God is not an ocean’ is a negative predication. It can be true. We don't need any semantic funny business to accommodate the slogan.¹¹

Of course, the slogan can't be right. ‘Positive predication’ and ‘negative predication’ are syntactic descriptions. Meanings do not come neatly sorted into positive and negative. With enough ingenuity (and a working knowledge of the lambda calculus), any complex sentence (including one involving negations) can be rendered into the form Fa. The core of an apophaticist view is more perspicuously put as something like: God is sufficiently transcendent/different from ordinary things that our concepts are simply inapplicable to God. Trying to say ‘God is good’ fails not because God is the opposite of good, but because God is so different from anything in our experience that the predicate ‘good’ isn't adequate to describe whatever axiological features God may have.

Once again, we don't need any semantic funny business. For the sentence ‘God is good’, in order for the argument against using it is to get off the ground, ‘good’ has to mean what it means in ordinary contexts (exactly what semantic continuity demands), and it should mean more or less what we thought it did (what semantic conservation demands). If ‘good’ receives a special meaning in theological contexts, then maybe it will turn out to be true that ‘God is good’. There could be a view like that, but it wouldn't be an apophatic one.¹²

This brings us to the lowest tier of principles: logical conservation and transparency. It may be surprising to some readers to see logical conservation on the lowest tier. After all, isn't reduction to inconsistency with logic the sina qua non of philosophical refutation? Perhaps once. But we already know that logic behaves badly when certain concepts are allowed to sneak into the object language, concepts like truth and meaning (reflect, both on these three words – I am lying – and the reams of complex, technical work they have inspired). Perhaps theological concepts, like semantic concepts, have an unanticipated effect on logic. None of this is to say that logical conservation would not be a nice thing to have. But losing it would not threaten the very premise of Christological inquiry the way losing theological conservation, semantic conservation, or semantic continuity would.

transparency, like logical conservation, is a nice thing that we already know we cannot always have. It would be beautiful if our natural language were a perfect mirror of itself, so that syntactic simplicity never hid semantic complexity, and a perfect mirror of the world, so that semantics were a flawless guide to metaphysics. But we know that's not so. Losing transparency is losing a nice thing, but it does not undermine the inquiry either.

Now that we have familiarized ourselves with the fundamental problem and rules for its acceptable resolution, we move on to qua-Christology. As we shall see, most members of the qua-family run afoul of the more important principles. But one will emerge relatively unscathed.

Qua-devices

One venerable approach to the fundamental problems interpolates the phrase ‘qua N’, where N is a nature, into the simple subject-attribute sentences that feature in the derivations of the contradiction.¹³ These qua-devices must then serve to prevent the contradiction between sentences like (5) and (6). There is not one strategy that is the qua-strategy. Instead, it is a family of strategies, with siblings differentiated by where they add the qua to simple sentences like (A).

(A) Christ is mutable

We will briefly review the siblings, before addressing each in turn.

(A*) Qua humanity, Christ is mutable.

(A**) Christ-qua-humanity is mutable.

(A***) Christ has mass-qua-humanity.

(A****) Christ has-qua-humanity mass.

Before we examine each, a distinction must be made. Qua-strategists do not assert that (A) really means one of (A*)–(A****). Instead, they assert that sentences like (A) have omitted an important part of the world's structure, namely the contribution that natures make to how subjects are tied to their attributes. Sentences like (A*)–(A****) are more metaphysically perspicuous than (A) and mirror the kinds of facts that can be used to give truth-conditions for sentences like (A). But the qua-strategy operates not at the level of semantics but at the interface between semantics and metaphysics.

Sentential qua-strategy

Beall and Henderson (2019) explore sentential qua. According to them, a sentential quaer aims to use her distinctive ‘qua n’ device as a sentential modifier, taking scope over the plain predications featured in the fundamental problem. What kind of operator? Here there is a split in the literature. Some discussion of qua-devices has entertained the thought that qua-devices express in-virtue-of claims.¹⁴ These authors suggest that (A*) means something like: in virtue of his humanity (or human nature), Socrates has mass. They then rightly observe that the following ‘release’ inference is good:

1. 1. in virtue of ϕ, P

   therefore,

2. 2. P

And if the release inference is good, then the sentential qua-strategy is a non-starter. The whole point of a qua-device is to override the qua-less sentence with the more perspicuous qua-sentence. The release inference turns the qua-device into a pointless runaround.

Instead, Beall and Henderson propose we see the ‘Qua-n’ operators as behaving like ‘according to’ operators. They see the role of natures in property instantiation as giving a kind of accounting of which properties a thing has, in the form of a story. They write:

It is natural to think of Christ's divine nature as delivering (i.e., entailing) a true story of anything that exemplifies that nature, where ‘story,’ in this context, need not be fiction – and isn't fiction in the case of the story of Christ. Similarly, it is natural to think of Christ's human nature as entailing a true story of anything that exemplifies that nature. Indeed, any nature delivers some true story of whatever possesses it – at the very least, the essential truths tied to that nature. We advance the 0-QUA view along just such lines: namely, the QUA device is an according to Nature operator. In particular, Christ's exemplification of two natures is accompanied by two distinct QUA devices: According to the Divine Nature and According to the Human Nature. The more standard (and perhaps more natural-to-the-ear) terminology of ‘story’ may equivalently be used provided that the core stories in question are entailed by Christ's two natures. Accordingly, one may think of the 0-QUA account as involving two sentential operators: namely, According to the Divine Story and According to the Human Story.¹⁵

This, they contend, solves the ‘release’ problem, since ‘according-to’ operators do not generally validate it (try the following: according to the liar, according to the internet, according to the fool).

It's not clear to me that Beall and Henderson have actually solved the ‘release’ problem. After all, the nature-stories are supposed to be true. And while ‘according-to’ operators do not generally release, factive according-to operators (e.g. ‘according-to-the-true-story-about’) do release. In fact, therein lies their factivity. Of course, if Henderson and Beall say that their operators don't release, they don't. That's the privilege of innovation. But it raises the spectre of violating the principle of logical conservation.

Moreover (and this will be a problem common to the qua-family), Beall and Henderson's view does away with transparency. Nothing in the surface grammar of (A) suggests that the facts in the world that verify it really have a structure like that of (A*). If we did not need According-to-the-divine-story and According-to-the-human-story operators for Christology, we would not otherwise think to look for them, nor would linguistic tests for concealed operators turn them up. So we also have a violation of the principle of transparency. They admit as much:

As with all Qua-solutions the explicit statement of the relevant truth requires the Qua-device – in the 0-QUA view, the according to device. Any truth in ‘Christ is mutable’ – similarly, ‘Christ is immutable’ – is elliptical for an essentially QUA-involving claim. (Beall and Henderson 2019, 160)

And so we move on to the other qua views.

Subjective qua-strategy

The next type of qua-strategy, associated with modifying sentences like (A) to sentences like (A**), puts the nature's intervention in the subject-position. The subjective qua draws a distinction between ‘Christ-qua-human’ and ‘Christ-qua-divine’. There are two distinct logical subjects. This dissolves the fundamental problem. Christ-qua-human is the mutable one; Christ-qua-divine the immutable one. Because these are distinct subjects, no communicatio idiomatum forces them to bear incompatible attributes.

The weirdness here lies in the two subjects. How do Christ-qua-human and Christ-qua-divine relate to Jesus of Nazareth and God the Son? That relation cannot be identity. The communicatio idiomatum holds that God the Son and Jesus of Nazareth share their attributes. Christ-qua-human and Christ-qua-divine do not share their attributes, on pain of rendering the qua-device pointless.

This problem of the subjects threatens to undermine theological conservation. There is only supposed to be one full-blown person in this story. Christ. Yet on this qua-strategy, both Christ-qua-human and Christ-qua-divine are people.¹⁶ Humanity and Divinity both carry personhood. And yet Christ is neither Christ-qua-human nor Christ-qua-divine. Christian theology has always had issues counting persons, but this is out of hand.¹⁷

Attributive qua-strategy

The attributive qua-strategy focuses not on the subject, but on the attributes. Christ is mutable-qua-human and Christ is immutable-qua-divine. Where once we thought we had two attributes, mutable and immutable, we end up having four attributes: immutable-qua-human, immutable-qua-divine, mutable-qua-human, and mutable-qua-divine (actually, we end up with indefinitely many more, since there will be F-qua-N for every possible nature).

The attributive qua-strategist avoids the theological problems suffered by the subjective qua-strategy. Instead of multiplying subjects and causing a counting problem, she multiplies attributes. Fortunately, predicates are sufficiently cheap that this multiplication of attributes (which, even if we have infinitely many attributes and infinitely many possible natures, will not get us more than the larger of those two infinities) shouldn't concern us. The violation of semantic conservation it heralds, however, should. The attributive qua-strategy can uphold semantic continuity, by insisting that just as Jesus of Nazareth and consequently Christ is mutable-qua-human, so we regular humans are also mutable-qua-human. One and the same predicate gets used when two things have the same nature. But the mutability of a cat is not the same attribute as the mutability of a person. Where before we could say: ‘Humans, cats, buildings, and planets are all mutable things’, we now must say something different. These four different natures have different mutability properties. In fact, the mutability of humans and the immutability of God are no longer complements. We have changed the meaning of ‘mutable’ and ‘immutable’ by adding a qua-modifier, escaping the fundamental problem by talking about something else.

Copula qua-strategy

By contrast, the copula qua-strategy leaves both the subject and attribute intact. Instead, it locates the qua-device in the copula, the tie that binds subject to predicate. According to copula quaers, Christ is-qua-human mutable and Christ is-qua-divine immutable. The copula qua-strategy does not multiply subjects or attributes. Instead, it requires that putting a subject together with its attributes must be done with reference to the subject's nature.

This will doubtless seem unfamiliar to many readers, so it bears taking a moment to go into some details. As a general feature, certain bits of language require other bits to represent a complete fact. This is most clearly seen in predicates, where a term like ‘loves chocolate’ is missing something. Logicians call these empty places in predicates open argument slots, and the number of things it takes to turn a bare predicate into a complete thought is called its arity. The qua-theorist proposes that copulas, like predicates, have argument slots that must be filled in order to form complete facts. Failing to fill the argument slot leaves the copula unsaturated, and the fact represented incomplete. What is missing? A nature. The copula qua-strategist is thereby committed to a metaphysics of natures where what nature a thing has is intimately connected to what attributes it has. Historically, users of qua-devices were happy to take on these commitments. In the ordinary case, since most things only have one nature, the copula's argument slot wasn't worth mentioning. But then along came the incarnation, a successful theory of which requires acknowledging these hidden variables.

Since, to my knowledge, orthodoxy has nothing to say about copulas, there is no threat to theological conservation from this strategy. Unlike the subjective qua-strategy, it does not make a hash out of the person count. Nor does it violate semantic conservation. ‘Christ’, ‘Immutable’, and other key terms will mean exactly what we thought they meant before beginning Christological inquiry. ‘But wait’, one might ask, ‘what about “is”?’ Haven't we suddenly come up with a bunch of different ways to have an attribute, so that I have my attributes in a different way from a cat, when before we thought that the cat and I had our attributes in exactly the same way?

On this point, two remarks. First: there is still a substantial sense in which the cat and I have our attributes the same way. Each of us has them qua our own nature. It wouldn't do for either of us to have them qua some other nature. But second, and even more to the point, this objection misses the proposal. The proposal is not that there are a bunch of different copulas, each of which is used when appropriate. It is that one and the same copula is unsaturated, like a bare predicate is. And just as a bare predicate requires subjects to fill its argument slots to round out a simple sentence, the copula qua-strategist says that the copula requires a nature to fill an open argument slot to round out the sentence. A metaphysics where subjects have attributes qua their natures requires us to alter the way we thought copulas worked in order to represent the world perspicuously.

It is also worth noting that Christology is not the only area of metaphysical inquiry where thinkers have argued that a more complex copula may be required. One of the main solutions to David Lewis's problem of temporary intrinsics¹⁸ involves adding a time or tense to the copula.¹⁹ The parallels between that argument and the fundamental problem are evident as soon as one looks at rigorous presentations of the temporary intrinsics argument (e.g. as in Merricks 1994 and Rubio 2019) side by side with the fundamental problem. Pawl (2016b) goes into a fair amount of detail working out parallels between Christology and temporary intrinsics.

As with semantic conservation, so with semantic continuity. The qua copula is not just for Christology. Everyone has-qua-N their attributes, for appropriate values of N. The rules governing meaning do not change when we enter the Christology room.

What about logical conservation? Pawl (2016a) has tried to accuse the copula quaer of revising logic. This is mistaken; for further discussion see below. Allowing quantification into the copula is formally harmless.

This leaves transparency, which the copula quaer loses along with all of the other qua views. But one principle out of five, and that the least important, is an excellent performance for the view.

Non-qua views

Now that we have found the best qua view, it is worth using our assessment criteria to see how the best qua view stacks up against other major contenders in the literature. We will briefly explain the Christological theories of Tim Pawl, Richard Swinburne, and Jc Beall and compare them to the copula qua view. As we shall see, the copula qua view emerges triumphant over the views of Pawl and Swinburne, but the comparison with Beall ends in a stalemate.

Pawl's view

Tim Pawl offers a resolution of (5) and (6) by systematically reinterpreting the predicates involved. He proposes schema p as a way of avoiding the contradiction.²⁰

schema p: a is F iff a possesses a nature that is F.

Returning to (5) and (6), the Pawline solution will say that (5) does not mean what we had thought, that Christ cannot change. It instead means that Christ possesses a nature that cannot change. Likewise, it will say that (6) does not mean what we had thought, that Christ can be changed. It instead means that Christ has a nature that can be changed. In fact, Pawl must say even that very ordinary predications, like ‘The barn is red’, do not mean what we had thought they meant. They instead mean things like ‘the barn has a nature that is red’.

As Pawl notes, in the ordinary/one-natured case, his reinterpretation is a distinction without a difference. Assuming that everything has one nature, there is no meaningful difference between ‘x is F’ and ‘x has a nature that is F’, beyond the fact that the second sentence sounds somewhat stilted and commits itself to a metaphysics of natures.

It is important to note the difference between Pawl's view and the predicative qua-strategy. The predicative strategy replaced every predicate F with a family of predicates, ‘F-qua-n’, with a member for every nature n. This leads to problems such as being unable to say things like: here are some mutable things: cats, buildings, cars, me. Pawl's view handles this sentence well, reinterpreting it as ‘here are some things that have a nature that is mutable: cats, buildings, cars, me’. These will be true in more or less the same circumstances, at least given a background metaphysic of natures. Pawl's view is an improvement.

But how does Pawl's view stack up against the best qua-strategy, the copular view? And how does it stack up on our five criteria?

On theological conservation, Pawl's view is spotless. Pawl works hard to ensure that his view is consonant not just with the pronouncements of orthodoxy, but with the background views of the church fathers. This is probably more than theological conservation requires, and it certainly is sufficient.

On semantic conservation, on the other hand, Pawl scores poorly. The pretheoretical approach to predicates like ‘mutable’ and ‘immutable’ is to see them as meaning contradictory attributes, and more generally there's a strong presumption in favour of an equivalence between ‘the x is not F’ and ‘it is not the case that x is F’. Pawl's view sets this presumption aside. Pawl attempts to assuage this setting-aside, but is not shy that it is a commitment of his. On semantic continuity, on the other hand, Pawl scores well. schema p is fully general and does not posit any major discrepancy between the rules for setting the meaning of terms between theological and non-theological contexts.

Likewise, Pawl's view scores well on logical conservation. Nothing in schema p requires a change in our normal logics, although it does advance a revisionary semantic theory that complicates the mapping between sentences in ordinary and logical languages. Finally, Pawl's view stumbles on transparency. Nothing in the syntax of ordinary expressions suggests something like schema p, adding darkness between linguistic representation and linguistic meaning.

This leaves the copular qua view in a favourable position over Pawl's view. While both require failures of transparency, the copular qua view preserves semantic conservation.

Swinburne's split-mind view

A second significant contender is Richard Swinburne's divided mind Christology. For Swinburne, to be divine is to be essentially divine, but to be human is not to be essentially human. It is instead to come in some to way possess a suite of humanish attributes. Thus, for Swinburne, God the Son comes to be human when God the Son decides to become the soul of the incipient human body of Jesus of Nazareth. However, the Son does this by creating a mental subsystem within the Son's larger soul that has a distinctively human psychology. For a committed dualist like Swinburne, this is sufficient for a divine person also to become a human person. Christ can then act out of this subsystem in order to act as human, while still retaining his divine identity because his entire soul contains both the Son's normal divine operations and the specially made human subsystem.

According to Swinburne, Christ's consciousness is divided (on a Freudian model), with God the Son associated with a ‘divine’ part of the mind, and Jesus of Nazareth associated with a ‘human’ part of the mind. Difficult predicates like (5) and (6) are then to be interpreted as a kind of in-virtue-of claim (although the specific example of mutability does not work well here, because Swinburne simply denies that immutability is a divine attribute). Thus, for Swinburne, Christ suffered in virtue of having a human body and mental subsystem that experience suffering, even though Christ's divine mental system is impassable. Likewise, Christ's knowledge is limited when restricted only to the human subsystem but Christ is omniscient when his full mental life (including the divine subsystem) is considered.

Thus Swinburne solves the fundamental problem by discarding one or the other of conflicting predicates, while offering that the discarded predication is true when our attention is restricted to the purely human or purely divine subsystems of Christ's person. As a whole, Swinburne's Christ ends up with a hotchpotch of attributes, with some traditionally human characteristics such as passibility and mutability, and other traditionally divine attributes, such as omnipotence and omniscience. The communicatio idiomatum does not survive; we cannot fully attribute limitations of knowledge or of power to Christ, as we can on the qua and Pawline theories. This is a failure of theological conservation, and so a decisive advantage for the qua-theory.²¹

Swinburne could perhaps avoid the failure by taking on Pawl's revisionary semantic theory. He has lined up the metaphysics to do so easily, and it would not compromise the spirit of his view. Were he to do so, the comparison would then proceed in the same manner, with theological conservation preserved at the price of semantic conservation and transparency. Yet the comparison with the best qua view would still favour the qua-theory.

Beall's contradictory Christology

A final comparison. Jc Beall has argued that nothing is wrong with any of (1)–(6).²² They require no semantic revision or metaphysical finessing. Instead, the problem is our move to place ⊥ after (6). If the logical consequence relation governing Christological theories is classical, then the ⊥ is warranted. But if the consequence relation is instead that of First-Degree Entailment (FDE), this is not so. Sentence pairs P, ¬P do not necessarily contradict in FDE.

Explaining the technical details of Beall's preferred consequence relation would take us too far afield; interested readers will find Beall's own explication more than adequate. Instead, we should take a minute to observe all of the benefits Beall's embrace of a classical contradiction buys him. We get theological conservation immediately. There are no conciliar statements on the correct consequence relation for theological theorizing. We get semantic conservation free and clear. We have no pressure to modify the meaning of any of the terms in (1)–(6) from Christology. We get semantic continuity if we want it. There is no pressure to make an exception to the rules of meaning for theology from Christology. Assuming we haven't lost it elsewhere, we also get transparency.

Thus the battle between Beall's view and the qua view (and mutatis mutandis the other views) comes down to how we trade off logical conservation and transparency. Beall does a fair amount of work to motivate abandoning logical conservation, but a similarly principled case may be made against transparency. Here we seem to have a stalemate.

Final objections

In this section, I address two standing objections to qua-theories. One accuses the copula quaer of revising logic, but is based on a misunderstanding of what it would take to transparently incorporate quantification into the copula into a first order language. The other asks the quaer for an account of predication simpliciter, the qua-less sentences we started out with. I give a supervaluationist response.

Logic and the copula strategy

Pawl (2016a) claims that the copula qua-strategy requires a logical revision. He presses the point by observing that the textbook formulation of first order logic does not include argument slots for quantifying into the copula, and therefore does not represent the structure that copula quaers insist is there in the facts that make sentences true.

This is true, but not yet enough to qualify as demanding a revision. There are generally three ways of revising a logic. We can expand a logic, so that it has the resources to say things that could not be said without those resources. Plural logic is one such example; adding plural quantifiers allows us to say things that could not be said with only first order resources. A classic example for the sceptical to try and say with only singular first order quantification: some critics admire only each other. We can also contract a logic. Doing this allows us to say only a subset of the things we could say in stronger logics. If we were to remove all truth functions from standard predicate logic, we would achieve such a contraction, since we would no longer be able to negate, conjoin, or disjoin any expressions. Finally, we can alter the consequence relation of a logic. This may not involve any difference in what the logic can represent, but it will change its theorems. Intuitionistic Logic and First-Degree Entailment are both revisions of classical logic, using the same formal language but with different consequences/validities.

Pawl does not say which of these revisions he accuses the copula quaer of being committed to. But his complaint points to the first. It's worth noting that many expansions of standard first order logic, such as plural logic, are benign. Yet in this case, even this charge is not apt. To show why, I will sketch a ‘revision’ to standard predicate logic that would allow us to represent the copula argument slot, and in so doing will deliver us a notational variant on classical predicate logic.

In order to include quantification into an argument slot in the copula, we need a few new pieces to the standard logical puzzle (I will assume familiarity with basic logic here; see Sider 2010 for the necessary background). We will want a special quantifier for quantifying into the copula. We will want some new variables associated with this quantifier. We will want to differentiate the values of these variables in the domain of discourse, perhaps by changing it from a set to a set of sets, one of these the usual set of objects and the other a set of values for these new variables, which I will call ‘natures’.

Now we need some place for the variables to go. By convention, we'll put them right before the object-variables in a predicate. So now n-place predicates are n + n place predicates (odd-place predicates are ill-formed). But even though the arity of the predicate changes, we are not adding extra relata. We are instead representing the nature qua which the subject(s) satisfy the predicate. The first n/2 argument slots in our newly expanded predicates must always be filled with (a) nature variable(s), which may only be bound by the nature quantifier.

Likewise, we need to tighten up the rules for an interpretation function. Instead of simply associating each predicate with sorts of ordered tuples drawn from the domain of discourse according to its arity, the function now associates each predicate with a set of ordered tuples where the first n/2 member comes from the set of natures and the other members all come from the set of objects. Intuitively, the ordered set begins with the natures involved, in order of appearance, and concludes with the objects involved, in order of appearance.

That's about all we need to do. And now that it's done, it's apparent that all I have done is describe a many-sorted first order language with some conventions about which variables go where in the predicates. It is well-known that many-sorted first order languages are expressively equivalent to single-sorted first order languages.²³

So I have not expanded the logic. Nothing you can express with the extra sort couldn't be expressed with one sort; we just made the expression cleaner. More transparent, you might say. I have also not contracted the logic. And I have not changed the consequence relation. In the reduction scheme, wherever something implied something else in the many-sorted language, their single-sort images do the same. The objection fails.

The fate of the qua-less

There is another question to clear up before our defence of the qua-strategy is complete. We have argued that a Christological theory where property-possession is indexed to natures fares better than its finest rivals when evaluated for theological conservation, semantic conservation, semantic continuity, logical conservation, and transparency. But given that the posit of a nature index in the copula of sentences that mirror reality's underlying structure more closely than ordinary language does is unfamiliar, we owe an account of how these sentences relate to everyday qua-less sentences.

In our view, a qua-less copula is like a predicate with an open argument place. This leaves a qua-less sentence akin to an open formula (that is: one containing a free variable). Often enough, open formulae are not even taken to be evaluable for truth, but rather for something like satisfaction. But when they are given truth conditions, it is as equivalent to their universal closure. To illustrate the proposal, we will use the example sentence (B): John is running.

The universal closure of B says that for every nature n, John is-qua-n running. This will of course be false. John only has the one nature, humanity, and therefore only is-qua-humanity running. It is not the case that he is-qua-divinity running, or is-qua-bovinity running. This won't do.

Fortunately, a solution readily presents itself. The problem with the original proposal is clear: it neglects the fact that most things only have one nature. We could attempt to fix the issue by restricting the universal quantification to natures possessed by the subject. Under this proposal, (B) is true just in case John is-qua-humanity running, which if he runs at all he must be, since all of his properties are had qua humanity. For the familiar universe of one-natured things, this proposal will deliver true qua-less sentences whenever anything is-qua-its-nature anything, and under no other circumstances. That is exactly the right result.

What about for multi-natured beings, like Christ the Redeemer? In that case, it is appropriate to say that the multi-natured a is F simpliciter only if it is F qua each of its natures. Thus, for some predicates, such as ‘is self-identical’, it will be appropriate to say Christ bears them simpliciter. But for those attributes which Christ has only qua one nature, it will not be appropriate to say either that he has it simpliciter or that he lacks it simpliciter. The truths in these cases are exhausted by the qua truths.

This approach will have the virtues and vices of supervaluation. Truth for qua-less sentences will be supertruth; the logic of qua-less sentences will be the logic induced by supervaluation. I have nothing to add to the criticisms and defences of supervaluation,²⁴ but hasten to note that the fate of the qua-less sentences is only somewhat important to our project. They are our starting point, but they turn out to be defective – incomplete in their representation of the facts that verify them. Just like it's not crucial to make open sentences truth-evaluable in first order languages, despite the important logical role they play, it's not crucial to make qua-less sentences truth-evaluable, despite the important role they play in starting the inquiry.

Trinity and unity

One of the primary advantages Beall claims for his paraconsistent view is the ability to provide a universal solution to logical problems in the Christian Doctrine of God, offering a solution not only to the fundamental problem of Christology, but also to the logical issues involved in the doctrine of Trinity.²⁵ It is commonly a virtue for, and a point in favour of, philosophical views to solve multiple problems in a unified way. So we might ask: what are the prospects of a qua-theoretic approach to the logical problems in the Trinity? In a word: dim. The central mechanic of all qua-solutions is the indexing of Christological statements to natures, in some way or other. This is a non-starter in the Trinitarian context. Orthodoxy insists that the persons of the Trinity share one nature (divinity), but are distinct on account of ‘person-distinguishers’.

Does this give an edge to contradictory Christology over qua-Christology? It's not obvious that it should. The core insight of the qua-solution is that the fundamental problem of Christology isn't at its core a logic problem. It is a metaphysics problem. Likewise, the qua-theorist should insist that the problems of the Trinity are not at their core logic problems. They are metaphysical problems. But they are problems not in the metaphysics of natures, but in the metaphysics of persons. It is consequently to the metaphysics of persons (and personal identity more specifically) that we should turn for a solution. What of the principle that we should seek unified solutions when we can? The qua-theorist should reject it in full generality. Instead, she should insist: we should seek unified solutions only for unified problems. Unified solutions for disunified problems might even seem a bit suspicious. This introduces an additional layer of methodological disagreement with the contradictory theorist, but maintains the stalemate.

Conclusion

I set out with two objectives: to lay out principles to guide Christological inquiry and to use those principles to show that qua-Christology is on at worst an even footing with its rivals. Drawing on a combination of literature and argumentation, I have proposed and ordered five principles that it would be nice for a Christological theory to satisfy (though to my knowledge none does). I then used those principles to pick from among the various qua-strategies the best, and compare it to other leading Christologies. Against Swinburne and Pawl, it holds a slight advantage. Against Beall, it ends in a draw depending on trade-offs between logical conservation and transparency. All in all, a fair showing.

Nevertheless, there remains work to be done. The qua-strategy is not primarily a logical or semantic strategy, but a metaphysical one. It will ultimately live or die with the ability of its proponents to deliver a metaphysics of natures that is (a) independently plausible and (b) fit for task within the theory. That task I bequeath to future work.