Reviewed by: Communicatio Idiomatum: Reformation Christological Debates by Richard Cross Aaron Moldenhauer Communicatio Idiomatum: Reformation Christological Debates. By Richard Cross. Oxford: Oxford University Press, 2019. 312 pp. Richard Cross takes a unique approach to the Christological debates among sixteenth-century Reformers. He does not survey the course of the debates, nor does he consider the many scriptural or patristic arguments raised. Instead, he limits his inquiry to a rigorous analysis of the metaphysical and semantic arguments made by Lutheran and Reformed theologians as they debated the communication of attributes. Cross’s goal is neither to judge which position is correct nor to provide a complete picture of the debates. Instead, he offers deep analysis of key snapshots in the course of the discussion that illuminate the metaphysical and semantic arguments. The result is a book that applies a typical methodology used to analyze scholastic philosophical theology to key moments of Reformation debates about the person of Christ. This approach situates Cross’s work among other works exploring the relation of the Reformers’ Christology to philosophy. Older analyses of Luther’s Christology, influenced by Reinhard Schwarz, argued that Luther broke cleanly with scholastic approaches to the person of Christ since Luther found late medieval metaphysics and semantics unsuited for Christology. Graham White’s Luther as Nominalist (1984) counters Schwarz’s approach by identifying continuities between the scholastics and Luther. In recent years works such as Joar Haga’s Was There a Lutheran Metaphysics? (2012) and David Luy’s Dominus Mortis (2014) have continued this conversation. Cross assumes two points debated in these and other works. First, Cross assumes that the Reformers made metaphysical and semantic arguments in their Christology. Second, Cross assumes that the Reformers knew and used scholastic Christology. The validity of these assumptions can be judged by assessing Cross’s work. An expert in medieval theology, Cross proceeds by [End Page 484] identifying and labeling arguments. While medieval theologians explicitly identified these arguments, the Reformers did not. Despite this difference in style, Cross argues that the Reformers raised metaphysical and semantic arguments and intended them to be taken seriously. Cross reduces key arguments to symbolic representation, using logical shorthand and identifying various positions by initials for ease of future reference. For instance, Cross isolates one of Luther’s arguments raised in his Christological debate with Ulrich Zwingli. Luther held that the two natures of Christ cannot be spatially separated without dividing the person of Christ. Accordingly, wherever Christ’s divine nature is, there Christ’s human nature must also be present. Otherwise the person of Christ is divided. Cross labels this argument as “impossibility of bodily separability” and abbreviates it as “the IBS principle.” He defines IBS as the argument: “If the natures lack two-way spatial inseparability, the person is not indivisible” (59–65). Cross’s list of such frequently cited principles runs close to two pages, showing the extent of his research into primary sources and the precision of his analysis. This type of analysis applied to the conceptually dense material of Reformation Christology demands careful attention from the reader. Cross succeeds in identifying metaphysical and semantic arguments raised by Reformers and in showing that the Reformers knew scholastic Christology, raising questions about how cleanly the Reformers broke with late medieval scholasticism. However, those interested in the debate will need to look beyond this book for a complete picture of Reformation Christology. Cross does not ask how important the arguments he analyzes were in relation to the scriptural, patristic, or other arguments raised. Nor does he ask how significant it is that the Reformers broke with medieval theologians as they pushed philosophical arguments to the background of their work. That is, the reader must recognize the limits of the study that Cross assigns himself. When the limited scope of the book is kept in mind, Cross’s work provides a window into an important facet of Reformation Christology and raises broader questions about the role of philosophy in Reformation theology. [End Page 485] Aaron Moldenhauer Concordia University Wisconsin Mequon, Wisconsin Copyright © 2021 Johns Hopkins University Press and Lutheran Quarterly, Inc