Consider this triad, and whether it is logically consistent:
1. The man Jesus = the 2nd Person of the Trinity.
2. The 2nd Person of the Trinity exists necessarily.
3. The man Jesus does not exist necessarily.
Each of these propositions is one that a Christian who understands his doctrine ought to accept. But how can they all be true? In the presence of the Indiscernibility of Identicals, the above triad appears inconsistent: The conjunction of (1) and (2) entails the negation of (3). Can this apparent inconsistency be shown to be merely apparent?
Reduplicatives to the rescue. Say this:
4. Jesus qua 2nd Person exists necessarily while Jesus qua man does not exist necessarily.
5. Jesus exists necessarily & Jesus does not exist necessarily.
And that is a plain contradiction. But that assumes that reduplicative constructions need not be taken with full ontological seriousness as requiring reduplicative truth-makers. It assumes that what we say with reduplicatives can be said without them, and that, out in the world, there is nothing that corresponds to them, or at least that we have no compelling reason to commit ourselves to reduplicative entities, qua-entities, one might call them. That assumption now needs to be examined. Suppose we parse (4) as
6. Jesus-qua-2nd Person exists necessarily & Jesus-qua-man does not exist necessarily
where the hyphenated expressions function as nouns, qua-nouns (to give them a name) that denote qua-entities. It is easy to see that (6) avoids contradiction for the simple reason that the two qua-entities are non-identical. But what is non-identical may nonetheless be the same if we have a principled way of distinguishing between identity and sameness. Essentially what I have just done is made a distinction in respects while taking respects with full ontological seriousness. This sort of move is nothing new. Consider a cognate case.
Suppose I have a red boat that I paint blue. Then we can say that there are distinct times, t1 and t2, such that b is red at t1 and blue at t2. That can be formulated as a reduplicative: b qua existing at t1 is red and b qua existing at t2 is blue. One could take that as just a funny way of talking, or one could take it as a perspicuous representation of the ontological structure of the world. Suppose the latter. Then, adding hyphens, one could take oneself to be ontologically committed to temporal parts, which are a species of qua-entity. Thus b-at-t1 is a temporal part that is distinct from b-at-t2. These temporal parts are distinct since they differ property-wise: one is red the other blue. Nevertheless, they are the same in that they are parts of the same whole, the temporally extended boat.
The conceptual move we are making here is analogous to the move we make when we say that a ball is green in its northern hemisphere and red in its southern hemisphere in order to defuse the apparent contradiction of saying that it is red and green at the same time. Here different spatial parts have different properties, whereas in the boat example, different temporal parts have different properties.
Can we apply this to the Incarnation and say that Jesus-qua-God is F (immortal, impassible, necessarily existent, etc.) while Jesus-qua-man is not F? That would avoid the contradiciton while upholding such obvious truths as that divinity entails immortality while humanity entails mortality. We could then say, borrowing a term from the late Hector-Neri Castaneda (1924-1991), that Jesus-qua God is consubstantiated with Jesus-qua-man. (Hector the atheist is now rolling around in his grave.) The two are the same, contingently the same. They are ontological parts of the same substance, and are, in that sense, consubstantiated. Jesus is God the Son where ‘is’ expresses a contingent sameness relation, rather than strict identity (which is governed by the Indiscernibility of Identicals and the Necessity of Identity).
The idea is that God the Son and Jesus are, or are analogous to, ontological parts of one and the same whole. This is an admittedly bizarre idea, and probably cannot be made to work. But it is useful to canvass all theoretical possibilities.