Christology has always proved a subject of controversy in Christian theology. Early Christians argued vociferously about whether or not Jesus Christ was even divine, let alone what it might mean, and what the implications might be, that he be both God and man in one person. The many debates over the proper understanding of the work and person of Christ occupied the writings of many of the fathers of the church and the deliberations of several councils. While the general outlines of the orthodox teaching on these matters might have been settled by the scholastic period, there was nonetheless much room for debate. Corey Barnes focuses here on the questions surrounding the doctrine of two wills in Christ, one human and one divine, from the twelfth century through to the early fourteenth century. More particularly, Barnes is concerned with the teaching of Thomas Aquinas, which he seeks to contextualize among that of other scholastic theologians.
That there are two wills in Christ follows from his two natures, or at least it was eventually seen to do so among orthodox theologians. If we take it as granted that Christ is fully human and fully divine, then he must have a human will and a divine will, or else his two natures would be incomplete. This much at least was agreed upon in orthodox circles. What are theologians to do, however, with Christ's prayer in Gethsemane (Mt 26:39: "My Father, if it be possible, let this chalice pass from me. Nevertheless, not as I will but as you will.")? If it is taken as given that there are two wills in Christ, what are we to make of this passage? Does Christ's human will act in a manner contrary to his divine will? Questions of contrariety and conformity became key for medieval theologians in the thirteenth century.
The Sentences of Peter Lombard set the framework for such discussions. Lombard arrayed most of the sources and distinctions that would be foundational for future discussions of the questions in Sentences III, d.17, where he asked whether Christ willed something that was not fulfilled. Lombard's first point is that Christ's prayer demonstrates that he possesses two wills, human and divine. That out of the way, he argues for a distinction in Christ's human will between will according to the disposition of reason and according to the disposition of sensuality; according to the first, Christ willed the passion, and according to the second, he shunned it. This distinction would be refined further by other theologians, based on their reading of John Damascene's De fide orthodoxa, into thelesis and boulesis: the will as nature (voluntas ut natura) and the will as reason (voluntas ut ratio) respectively. Allowing for a division in the human will of Christ opened up new avenues of exploration, even as it provided a tool for overcoming the problem of contrariety that might otherwise be drawn from Christ's prayer. William of Auxerre and the Summa fratris Alexandri both developed an argument against contrariety in Christ by recourse to this distinction in Christ's human will. The basic argument is that the objects of these distinct parts of the human will are distinct as well, and since contrariety must be circa idem et secundum idem, i.e., through the same or according to the same object, there could be no contrariety between them.
Thirteenth-century theologians would develop arguments based on this distinction, but major figures like Albert the Great and Bonaventure, rejected the circa idem et secundum idem line of argumentation. Albert actually allowed for contrariety of wills in Christ, but insisted on a conformity of Christ's human will with the divine will. Bonaventure on the other hand, rejected all contrariety of wills, while emphasizing conformity "as the most meaningful category for judging Christ's wills" (89). Albert is the more radical in his allowance of contrariety in the discussion, as he breaks with his predecessors in this regard. Shifting the discussion away from contrariety helps Albert to deal with the biblical witness by allowing that Christ's will as nature willed not to die, willing as the divine will willed it to do, and Christ's will as reason willed to die in conformity with the divine will. Albert insisted that there was no sin in this sort of contrariety, which he argued only occurs when there is a struggle of wills, which there was not in Christ.
Having clearly laid out the arguments of Aquinas' predecessors and the context for Thomas' formulation of his own opinions on the matter, Barnes turns in chapters 4 and 5 to a thorough exploration of Aquinas' teaching on Christ's two wills. At almost 200 pages, over half the book's length, these chapters form the heart of the book, and here Barnes' efforts bear the most fruit. Chapter 4 covers the development of Aquinas' teaching between the Scriptum and the Summa theologiae, noting developments in terms of emphasis, terminology, and in the use of sources. One such shift of emphasis was Aquinas' increased interest in the assumption of a perfect human nature into hypostatic union with the Word, part of a continual effort against Nestorian and other two-subject Christologies. A further development was an increased emphasis on Christ's free will as part of his perfect human nature. Terminological developments include the notion of a rational instrument, which allows Thomas to speak of Christ's human nature as an instrumental efficient cause of salvation, protecting the free choice of Christ's human will, but allowing it to be moved through the divine will toward the end of salvation. As to sources, the earlier Scriptum cites those found in Lombard's Sentences and the commentary tradition on that work, whereas the Summa adds to these the acts of Constantinople III and its sources, which replaced those works cited from the Lombard. This added the weight of conciliar authority to Thomas' discussion, including that council's rejection of contrariety of wills in Christ. The recovery of these sources did not revolutionize Thomas' understanding, but they were nonetheless an important piece of historical theology and proved more useful to Thomas than the sources cited in the Scriptum. Thomas had thus built upon, and in some ways surpassed, the work of previous theologians on the subject, as seen for instance in his rejection of his teacher Albert's allowance of contrariety of wills in Christ.
Chapter 5 develops from the technical discussions of chapter 4, exploring in detail Thomas' idea of Christ's human nature as instrumental efficient cause of salvation in the context of his emphasis on the Incarnation as a fitting means for humanity to be saved by God. Fittingness, convenientia, is a major unifying theme for Aquinas' understanding of the Incarnation, and Aquinas demonstrates at every turn how the Incarnation of the Word was the most fitting means for human salvation. In this case, Thomas demonstrates the importance and fittingness of Christ's perfect human will, which allows Christ's human nature to be a rational instrument, and the instrumental efficient cause of salvation, giving Christ's free will "an awesome role...in the work of salvation" (290), all the while maintaining an emphasis on the hypostatic union which safeguards against dividing the person and works of Christ.
Barnes ends his treatment with a short chapter on the later work of theologians on the matter, most importantly that of John Duns Scotus, who voiced several objections to Aquinas' teaching. Barnes identifies three areas of concern for other theologians about Thomas' conception of instrumental efficient causality and the Incarnation. First, there was a concern that discussing Christ's human nature in this way reduced his human actions to a role of secondary causality, making them the same as any other human actions. A second concern was that the cause of all actions in Christ would be assumed under the Word, and thus not be human actions at all. The third concern was that if Christ's human actions were instrumental efficient causes of salvation, these might be seen as troublesome for the doctrine of the unity of Trinitarian action ad extra, since they seem to be actions performed by the second person of the Trinity alone. Aquinas' continued emphasis on Christ's human nature as "hypostatically-united rational instrument" (322) answers the first two of these issues, but Barnes concludes that the third is the most challenging, and Aquinas' teaching "leaves itself vulnerable to challenges of violating the absolute unity of Trinitarian actions ad extra" (328).
Barnes' presentation and contextualization of Aquinas' mature teaching on Christ's two wills is clear, thorough, and highly readable. This is an excellent and rewarding book, and those interested in medieval theology, Thomism, or Christology, will be well repaid for reading it.