Aquinas, the Incarnation and the Relative Identity Thesis: A Modest Defense of the Assumptus-Homo Theory

75 The Thomist 79 (2015): 75-111 AQUINAS, THE INCARNATION AND THE RELATIVE IDENTITY THESIS: A MODEST DEFENSE OF THE ASSUMPTUS-HOMO THEORY CHRISTOPHER H. CONN The University of the South Sewanee, Tennessee HE MYSTERY OF the Incarnation tells us that, in the course of human history, the Word of God assumed our nature without ceasing to be who and what he has been from all eternity, the only begotten Son of God, the second person of the Holy Trinity. Thomas Aquinas was far from alone in insisting that our understanding of how this took place be properly grounded in our understanding of why it took place. The Son of God assumed our nature so that he might suffer and die on our behalf, that we might be saved from the curse of sin and death and restored to God’s friendship and the path towards our highest good: the beatific vision of God. Since only one who is human is in a position to suffer and die on our behalf, and since no mere human is in a position to offer such a condign sacrifice—one that satisfies the demands of God’s justice with regard to the whole of our race—it has long been an article of faith that the Incarnation involves one person who is both fully human and fully divine.1 For Aquinas, this means 1 For examples of this line of reasoning in Aquinas, see STh III, q. 1, a. 2; ScG IV, c. 54; and Comp. Theol. I, cc. 198-200. Quotations from the Summa theologiae are from the translation by the Fathers of the English Dominican Province (New York: Benziger Brothers, 1947). Quotations from the Summa contra gentiles are from the translation by Charles J. O’Neil (Notre Dame: University of Notre Dame Press, 1975). Quotations from the Compendium of Theology are from the translation by Richard Regan (Oxford: Oxford University Press, 2009). In the course of this paper I shall also be drawing upon Ralph McInerny’s translation of Aquinas’s Scriptum super libros T 76 CHRISTOPHER H. CONN understanding the Incarnation in a way that avoids the heresies of Monophysitism and Nestorianism.2 The former heresy fails to uphold the perduring reality of both natures, since it depicts them as blended into a single, theandric nature, according to which Christ is neither “perfect man” nor “perfect God.” The latter upholds the reality of these natures at the expense of Christ’s personal unity, since on this view the incarnate Christ involves two, numerically distinct persons, one of whom is human (Jesus of Nazareth) and one of whom is divine (the Eternal Word). Following Peter Lombard, Aquinas’s positive treatment of the Incarnation arises out of a debate between three accounts of this mystery which endeavor to avoid these theological hazards, accounts which have come to be known as the assumptus-homo theory, the subsistence theory, and the habitus theory.3 While all three accounts profess allegiance to the one-person/two-natures formula of the Incarnation, they differ markedly as to how these natures are related to one another and to the one person of Christ. As its name suggests, the assumptus-homo theory maintains that the Son of God assumed our nature by assuming a complete human being. Having thus united himself to this human being, the one person of Christ exists in relation to two beings or substances, namely, his original, divine substance (whom he has been from eternity), and an assumed, human substance (whom he has become). The subsistence theory categorically rejects this dualism of substances. On this account, the Son of God did not become an instance of our nature by assuming an instance of our nature. Rather, he became an instance of our nature by assuming those features which are essential to our nature, namely, a human Sententiarum, J. L. A. West’s translation of De unione, and West’s translation of Quodlibet IX, q. 2, aa. 1-2. While not readily available in translation, all three texts are available online at dhspriory.org/Thomas. 2 STh III, q. 2, a. 6. 3 In what follows I am primarily concerned with Aquinas’s understanding of...