From Chalcedon to contradiction

The Council of Chalcedon 451 affirms that Christ is fully divine and fully human, not mostly human and in-part divine, not mostly divine and in-part human, and not some other hybrid combination of divinity and humanity. Given classical conceptions of divinity and humanity, Chalcedon's account leads to apparent contradiction. This is what Richard Cross has dubbed ‘the fundamental problem [of the incarnation]’ (Cross (Reference Cross, Flint and Rea2011), 453). Example:

1. 1. Christ is mutable. [Rationale: entailed by human nature.]

2. 2. Christ is immutable. [Rationale: entailed by divine nature.]

3. 3. Christ is mutable and immutable. [Rationale: 1–2, logic.]

Likewise, mutatis mutandis, for im-/passibility, im-/peccability, im-/materiality, and so on for the many pairs of properties either entailed by the two natures (viz. divine and human) or otherwise affirmed in Christian creeds and orthodox theologies.

Standard routes towards consistency

Because the incarnation is at the very foundation of Christian theology, the fundamental problem demands a response. One might accept that the apparent contradictions are veridical;Footnote ¹ however, the dominant strategy, which we pursue here, seeks a logically consistent account of the incarnation, aiming to explain how the apparent contradictions of Christ are merely apparent. There are four, sometimes overlapping, routes towards consistency charted by Cross (Reference Cross, Flint and Rea2011).Footnote ²

• • Reduplication: here, ‘Christ is mutable’ and/or ‘Christ is immutable’ are shorthand for QUA-adorned truths – namely, ‘Christ-qua-human is mutable’ or the like, where different strategies put the QUA device in different places. The error in the given derivation is that premises (1) and (2) are insufficiently expressed: the truths involve QUA adornments that undermine the steps to (3).Footnote ³

• • Relative identity: here, the identity relation peculiar to Christology is a so-called relative one, famously explored by van Inwagen (Reference van Inwagen and Morris1988; 1994) and Martinich (Reference Martinich1978). The key here is that while, per Chalcedon, Christ is the same person as the human Christ and the divine Christ, the latter two beings are not identical beings, and so can consistently have two contrary properties (i.e. properties the joint having of which entails a contradiction) – as consistently as any two non-identical objects can each have exactly one of two contrary properties. The error in the given derivation rests on mistaken principles of theological identity relations.Footnote ⁴

• • Composition: here, the target predicates are (in effect) primarily applied to proper ‘parts’ (or aspects or what have you) – in the most general sense of ‘parts’ – of Christ, and only derivatively to Christ. Example: Christ's physical body is mutable but no divine ‘part’ of Christ is mutable. Here, the contradiction fails because an object counts as mutable in virtue of one of its mutable parts but also counts as immutable in virtue of an immutable part – no more inconsistent than ‘in-part green’ and ‘in-part red’, applied to one object, are inconsistent.Footnote ⁵

• • Restriction: here, the idea is that either the classical theory of divinity, which entails (2) in the target derivation, or the classical theory of humanity, which entails (1), should be rejected, and in turn the derivation of target contradictions fails due to faulty initial premises.Footnote ⁶

This list does not exhaust the theoretical landscape;Footnote ⁷ there are other options. Our aim is to outline an option that takes seriously the modal features of the target properties (e.g. im-/mutable, im-/passable, etc.).

Being explicit about possibility

Many of the fundamental-problem properties involve implicit appeals to possibilities.Footnote ⁸ This is the key to the target route towards consistency: the consistency of the incarnation is explained by the structure of possibilities induced by such a radical event. There are two core parts of the explanation: different modal operators, and the structure of modal space over which the given operators range.

For simplicity (but without loss of generality) we focus on the properties involved in the sample derivation: mutable and immutable. On their standard meanings, these properties are exemplified by an object x just if it's possible that x changes and, respectively, it's impossible that x changes. On standard treatments of possibility, these amount to the conditions that there's some world at which x changes and, respectively, there's no world at which x changes.Footnote ⁹ The current bi-modal option points to a distinction motivated by the target natures (viz. the divine nature and the human nature). Instead of recognizing only one modal operator at work in the Christological affirmations, the idea is to recognize two, each tied to exactly one of the two different natures. A natural way to express the two operators explicitly invokes the given natures:

• • It is divinely possible that . . .

• • It is humanly possible that . . .

On the standard account of possibility operators, possibility is relative possibility in a twofold sense: namely, that what is possible is in fact possible-at-w for some world w, and that what's possible-at-w is tied to a given ‘access relation’ which is a binary relation on some subset (possibly the entire set) of worlds in modal space.

The treatment of the two target possibility operators ties them to their own accessibility relations, say, R ^d for the divine-access relation and R ^h for the human-access relation. One relation picks out points of modal space that count as ‘divinely possible’ from a given world, and the other the points that are ‘humanly possible’ from a given world. (We say more about these relations in the next section.)

Where A is any sentence, and ◊_d and ◊_h the divine and human possibility operators, respectively, the standard truth conditions are in force:Footnote ¹⁰

• • ◊_dA is true at w iff there's some R ^d-accessible point x at which A is true.

• • ◊_dA is false at w iff for all R ^d-accessible points x, A is false at x.

• • ◊_hA is true at w iff there's some R ^h-accessible point x at which A is true.

• • ◊_hA is false at w iff for all R ^h-accessible points x, is false at x.

Moreover, one can use logical negation ~ to define the corresponding notions of impossibility, namely,

• • ~◊_dA is true at w iff ◊_dA is false at w.

• • ~◊_hA is true at w iff ◊_hA is false at w.

The idea, then, is that Chalcedon demands true possibility claims, but – in light of the very different natures involved – does not demand that such claims be univocal. In particular, while

1. 4. ◊_h (Christ changes)

2. 5. ~◊_h (Christ changes)

are clearly contradictory, and likewise while

1. 6. ◊_d (Christ changes)

2. 7. ~◊_d (Christ changes)

are equally clearly contradictory, what's not clearly contradictory are the two fundamental but different possibility claims:

1. 8. ◊_h (Christ changes)

2. 9. ~◊_d (Christ changes)

And that's the promise of the bi-modal approach towards a consistent account.

The structure of modal space

So far we have said very little to explain the philosophical underpinnings of the two modal operators and their accessibility relations; the approach, as it stands, could use some additional metaphysical motivation. We want to stress that the details could be filled in differently according to varying philosophical and theological sensibilities. The core modal solution requires only minimal modal constraints.Footnote ¹¹ Still, for concreteness and clarity, we put forward one (potential) metaphysical picture that makes sense of the approach.

Modality is concerned with possibilities. And on the usual story, modal operators look at maximal possibilities – namely possible worlds. We begin with a set W of possible worlds. Following Adams (Reference Adams1979, 224f.), we treat (i.e. model) each world w in W as a maximal consistent set of propositions. The set is maximal in the sense that for every pair of mutually contradictory propositions, one member of that pair is in the set. The set is consistent in the sense that no mutually contradictory propositions are in the set. We use ‘@’ as a name for the actual world, which is (modeled as) the set of all true propositions.

But possible worlds, so understood, do not exhaust the relevant possibilities; some (many) possibilities are not maximal in the given sense (above). On a standard usage of the term ‘possibility’, going back at least to Humberstone (Reference Humberstone1981), a possibility can be any part of a possible world – including, but not limited to, the world itself. And this is the key to understanding our two modal operators. Each possible world in W can be ‘split’, or partitioned, into two parts: the divine part and the created part. This is accomplished by dividing the set of propositions according to what they are about. If the proposition is about God as God is intrinsically, then it goes into the divine part of the world. If the proposition is about the created order, or about God in relation to that created order, then the proposition goes into the created part of the world.Footnote ¹² Each of these parts is a possibility – a consistent set of propositions (as any subset of a consistent set is consistent) – but not necessarily maximal.Footnote ¹³ Let D be the set of all divine possibilities, so understood, and H be the set of all created possibilities, so understood.

In some worlds, the ones where God becomes incarnate, a divine person has both a divine and a created nature.Footnote ¹⁴ This means there are divine and creaturely propositions involving one and the same person; the same subject appearing in both parts. Propositions like the one expressed by ‘Christ is begotten’ go into the divine part while the proposition expressed by ‘Christ changes’ goes into the creaturely part. But it is important to see that, in the case of divine incarnation, the same person may be the subject of both divine and creaturely propositions, and so may appear in possibilities in both D and H.Footnote ¹⁵

Our access relations R ^d and R ^h can now be defined. From a given world w, the divine-access relation R ^d ranges only over the (set of all) divine possibilities: R ^d is a relation from W to D.Footnote ¹⁶ Similarly, the human-access relation R ^h ranges only over the (set of all) created possibilities: R ^h is a relation from W to H.Footnote ¹⁷ As with standard semantics for other modalities, the exact behavior (e.g. entailments) of the target operators d and h can depend on the properties (e.g. reflexivity, transitivity, etc.) one's theory imposes on the governing accessibility relations. For now, our basic outline imposes no constraints on the given relations – leaving exact details of such properties for theological debate.

Towards a bi-modal solution

Recall that all possibilities (all points in D, H, or W) are sets of propositions. An atomic proposition's being true-at-a-possibility is just that proposition's being in the set. Dually, an atomic proposition's being false-at-a-possibility is just that proposition's not being in the set. Extending beyond atomic propositions: the standard truth and falsity conditions for the logical operators apply;Footnote ¹⁸ the key modal operators are defined via the truth and falsity clauses given above.Footnote ¹⁹

The full shape of the solution is now available. The claim ‘◊_h (Christ changes)’ is true at @ iff there's some R ^h-accessible point (hence, some point x in H) such that ‘Christ changes’ is true at x. There may be many creaturely possibilities at which ‘Christ changes’ is true, including the creaturely part of @. On the other hand, the claim ‘~◊_d (Christ changes)’ is true at @ iff there's no R ^d-accessible point (hence, no y in D) such that ‘Christ changes’ is true at y. But since y is in D that is, a divine possibility – y is a set of propositions about God's intrinsic nature. Traditionally, change is never attributable to God in se, and so the claim ‘Christ changes’ will never be in the divine part of any world – and so ‘~◊_d (Christ changes)’ is true at @. Hence, both immutability and mutability are made true (at the actual world), albeit relative to different modalities.

On the bi-modal solution, the apparent contradiction of Christ is only apparent. We disambiguate the implicit modalities involved in the salient pairs of (modal) predicates, understanding one as ranging over sets of propositions involving God intrinsically and the other as ranging over sets of propositions involving God in relation to created natures – including Christ's own human nature.Footnote ²⁰ Mutability is truly attributed to Christ via the it is humanly possible that operator, which ranges over created possibilities; immutability is truly attributed to Christ via the it is divinely possible that operator, which ranges over divine possibilities.

Summary

The aim of this discussion has not been to advance a detailed solution to the fundamental problem of Christology but rather to advance a strategy towards consistency, one that takes seriously the modal features inherent in (many versions of) the problem. The key lesson is twofold: first, the Chalcedonian demand for full divinity and full humanity is not a demand for univocal modalities. Two different modal operators, one ranging over divine possibilities and the other over creaturely possibilities, resolve the contradiction.

The bi-modal strategy towards consistency is novel and natural. Philosophers already recognize a number of modal operators: epistemic, deontic, temporal, logical, and nomological modalities. It's time for theologians to consider whether distinctively theological modalities do important theological work.Footnote ²¹