A recent argument of mine questioning the coherent conceivability of the one person-two natures doctrine of Chalcedonian Christology begins with the premise
1. If N is a nature of substance s, then s cannot exist without having N. Natures are essential to the things that have them. In possible worlds jargon: If N is a nature of s, then in every possible world in which s exists, s has N. (The modality in play here is broadly logical or metaphysical.)
I think the Aristotelian who wants to maintain Chalcedonian Christology could deny 1 and affirm a nearby proposition:
1’. For any one-natured substance s, if N is a nature of s, then s cannot exist without having N.
Adding the antecedent I’ve added to your 1 here allows for us to say that 1’ remains true in the case of Christ, since the antecedent is false. 1’ does all the work that the Aristotelian would want 1 to do, since every case we think of in mundane (non-christological) situations is a case where the thing in question is single-natured. I wouldn’t think the Aristotelian has any evidence for 1 that would not count as evidence for the revised 1’ as well.
The purpose of this entry is to evaluate Tim's response. But first some preliminaries.
Assumptions. Preliminaries, and Ontological Background
I am not questioning, let alone denying, the fact of the Incarnation. (To insert an autobiographical remark: I am inclined to believe it.) Thus I am not maintaining that there is no sense in which, in a sentence from the Angelus, 'the Word became flesh and dwelt among us." My question is whether the Incarnation is coherently conceivable within a broadly Aristotelian ontological framework. A negative answer, should one be forthcoming, does not foreclose on the question whether the Incarnation is coherently conceivable within some other ontological framework.
By 'coherently conceivable' I mean 'thinkable without broadly-logical contradiction.' Coherent conceivability is a notion weaker than that of (real as opposed to epistemic) possibility. I am not asking whether the Incarnation is possible, but whether it is coherently conceivable (within a broadly Aristotelian framework). Conceivability is tied to our powers of conception; possibility is not.
Whatever is actual is possible. So if the Incarnation is actual, then it is possible whether or not we can coherently conceive how it is possible, whether or not we can render it intelligible to ourselves, whether or not it satisfies the exigencies of the discursive intellect. So if it should turn out that the Incarnation is not coherently conceivable, the defender of the Incarnation has a mysterian move available to him. He can say, look, "It's the case; so its possibly the case; it's just that our cognitive limitations make it impossible for us (in this life) to understand how it could be the case." The present topic, however, is not mysterianism.
My precise question is this: is it coherently conceivable that one person, the Second Person of the Trinity, the Word of God, the Logos, have both an individual divine nature and an individual human nature? I will assume that a person, as per Boethius, is an individual substance of a rational nature. I will also assume the doctrine of the Trinity.
'Substance' is elliptical for 'primary substance' or 'individual substance' or 'first substance' (prote ousia). If abstract entities are entities that are non-spatiotemporal and causally inert, then individual or individualized natures are not abstract entities. Some of them are spatiotemporal, and all of them are causally efficacious. Thus the individual nature of Socrates is in space and time. (The individual nature of the Logos is not in space and time but it is causally efficacious.) What ties an individual substance to its individual nature is not the external asymmetrical nexus of exemplification: substances don't exemplify their natures; a substance is (identical to) its individual(ized) nature. (See Aristotle, Metaphysics, Z.6) Socrates is not a bare particular, and his nature is not a (conjunctive) property that he exemplifies. Of course, there is a sense in which Socrates and Plato are of the same nature in that both are human. This common humanity, however, has no extramental reality: it is not a platonic object exemplified by the two philosophers.
The nature or essence of an individual substance is the what-it-is of the thing or as Aristotle puts it, to ti ên einai, literally “the what it was to be” of a thing, essentia, quod quid erat esse. (Compare Hegel: Wesen ist was gewesen ist.) It follows that the nature or essence of Socrates is not accidental to him. The idea that the nature of an individual thing could be accidental to it is wholly un-Aristotelian, although it would make sense in an ontological scheme according to which Socrates is a bare particular and his nature is a conjunctive property the conjuncts of which are his non-relational properties. (We find such a scheme in D. Armstrong and R. Grossmann, et al.)
It also seems obvious to me that there is an important difference between the event or fact of the Incarnation and any theological doctrine about it. Theology, I take it, is a type of applied philosophy: it is philosophy applied to the data of revelation. The Incarnation is one such datum since it is God's self-revelation in Jesus Christ. So it seems obvious to me that we ought to distinguish the datum from its doctrinal formulation. To repeat myself, I am concerned with the latter.
Evaluation of Tim Pawl's Response
Tim makes a time-honored move in alleviation of the contradiction that issues from my reductio ad absurdum argument: he makes a distinction. One can always avoid or remove a contradiction by making a distinction. He distinguishes between one-natured substances and substances that have more than one nature. He then restricts my (1) to one-natured substances. The result of the restriction is (1'). Accordingly, it is only one-natured substances that are under the requirement that their natures be had by them essentially. Now if we plug (1') into my argument in lieu of (1), no contradiction results. Although a one-natured substance has its one nature essentially (in every world in which the substance exists), a multi-natured substance may have a nature that it has accidentally (in only some of the worlds in which the substance exists).
Unfortunately, this trades one problem for another. For now the problem is to understand how an Aristotelian substance that has two natures can have one of them accidentally. The Logos exists necessarily. In the patois of possible worlds, it exists in every possible world. And it is divine (has the divine nature) essentially, i.e., in every world in which it exists. Since it exists in every world, it has the divine nature in every world. But it has the human nature only in some worlds. So the Logos has the human nature accidentally.
The problem is: How can any substance have a nature accidentally? Don't forget: we are operating within an Aristotelan framework and our precise question is whether the one person-two natures doctrine is coherently conceivable within that framework. As I said above, the nature or essence of an individual substance cannot be accidental to it. (The connection between a substance and its nature cannot be assayed as the external asymmetrical nexus of exemplification.) The idea that the nature of an individual thing could be accidental to it is wholly un-Aristotelian.
To sum up. Professor Pawl makes a distinction between single-natured substances which stand under the requirement that their natures be had essentially by them and multi-natured substances that are not subject to this requirement. This distinction blocks the contradiction my reductio issued in. But Pawl's distinction does not succeed in rendering the Chalcedonian formulation coherently conceivable within the Aristotelian framework because it requires a notion that makes no sense within that ontological framework, namely, the notion that a substance can have a nature accidentally.
To modify the Aristotelian framework in that way is not to extend it or enrich it in the light of new data, but to destroy it. What the Christologist ought to do is reject the framework. He needn't abandon the Incarnation. There are other approaches to it. I hope to sketch one in a separate post.