- Using Models for the Hypostatic Union: Lessons from Aquinas and Scotus1
AT THE HEART of Christianity is belief in the hypostatic union: The second person of the Trinity, the Son or the Word, took a human nature to himself in such a way that divinity and humanity are united in one person or hypostasis, that hypostasis being none other than the second person himself. To say this is one thing, to understand it is another, and the theology of the hypostatic union is the attempt to understand it. There is an important sense, of course, in which this cannot be done: the hypostatic union, like other theological mysteries, is beyond human comprehension. On the other hand, even if it cannot fully be grasped, it can be understood to a certain degree.
When trying to understand the hypostatic union, or to explain it to others, theologians often compare it to something else. That they do this is obvious enough, but what is perhaps less obvious is what is really going on when they do it, and what should be going on. One might think at first that a comparison is a mere decoration, a way to liven up our otherwise boring scientific accounts, but there may be more at stake than that. Consider, for example, how Richard Cross assesses Aquinas’s use, as a model for the hypostatic union, of the union of a concrete part and the whole to which it belongs. On Cross’s understanding, Aquinas thinks that whole and part make a good model because concrete parts do not contribute any esse, any existence, to the wholes to [End Page 103] which they belong, even as the assumed human nature does not contribute any esse to Christ.2 But the reason concrete parts contribute no esse, says Cross, is that they belong to the essence of their wholes. Therefore, use of this model leads to the view that Christ’s assumed humanity belongs to his divine essence, which is another way of saying that use of this model leads to Monophysitism, a view condemned by the Council of Chalcedon in 451. Now of course Cross knows that Aquinas is against Monophysitism, so his view in the end seems to be that Aquinas lands not in heresy but in inconsistency.3 I think Cross’s criticism of Aquinas grows out of a misunderstanding of how Aquinas uses models, and out of a misunderstanding of how models ought to be used.
As the reader may have noticed, I slid, over the course of the preceding paragraph, from the language of “comparison” to the language of “model.” Although I do not have any sharp distinction in mind, I think it is probably more natural to say “comparison” or “similitude” when something loose and undeveloped is at issue. For example, if someone casually says that the Word took on human nature the way you or I might put on a coat, and then quickly moves on to another topic, it would seem pretentious to call this a “model.” But if someone makes a comparison and then discusses it at some length, highlighting various aspects and using it to bring out important points, then the comparison is, we might say, no mere comparison, but a model.
In this article, I look at some writings of Thomas Aquinas and also at some writings of John Duns Scotus, focusing on two comparisons that seem sophisticated enough to merit the title “model” and that are, at any rate, labelled as such in the literature: the whole-part model, and the subject-accident model. Speaking in a somewhat historical mode, I try to make clear how Aquinas and Scotus deal with the two models just mentioned. I [End Page 104] then switch into a more systematic register and discuss how models ought to be used in discussions of theological topics.
I. Narrowing the Focus
Aquinas compares the hypostatic union to quite a number of things. Sometimes he is explicit, and other times less so. The following is an incomplete list, drawn mostly from the Summa theologiae. Aquinas compares the hypostatic union to
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• the union of soul and body;4
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• the union...