Students of the Protestant Reformation may remember Cardinal Cajetan (Thomas de Vio Cajetan) as Martin Luther's key opponent during a crucial early phase of the reformer's public career. At a famous face-to-face confrontation at Augsburg in October 1518, Cajetan called Luther to account concerning the definition of merit, the nature of indulgences, and the authority of the pope in relationship to Scripture. When Luther was unyielding, Cajetan contributed the substance to a papal bull that, while correcting several abuses connected to indulgences, also stood fast in condemning much of Luther's teaching.

Catholic scholars, by contrast, know Cajetan as an influential commenter on the works of Thomas Aquinas whose interpretations decisively influenced centuries of theologians in their approach to the 13th-century Dominican. In this book, however, Joshua Hochschild deals with a work of Cajetan's that he feels has been misinterpreted as simply part of Cajetan's work on Aquinas. That work was published in 1498 as De Nominum Analogia. Hochschild's argument is that, rather than only an extended footnote to what Aquinas had written about analogy, Cajetan was making his own arguments in responding to a challenge offered by Duns Scotus after Thomas passed from the scene. Scotus attacked Aquinas' reliance on analogy as a key way of reasoning about the relationship between divinity and humanity (and about much else). Thomas had defined analogy as mediating between univocation (clear naming of a real thing) and equivocation (irremediably ambiguous speaking about a thing). Cajetan's response, and according to Hochschild his advance beyond Aquinas, was to define proportion as a way of preserving the foundational usefulness of analogical reasoning. In making this case, Hochschild wades through high philosophical waters involving "simple apprehension, complex judgment, and discursive reasoning … the distinction between perfect and imperfect concepts; abstraction and 'confusion'; predication and nonunivocal universality; definition, and the significations of relations … analogy in discursive reasoning and the avoidance of fallacy." If readers can keep their heads about the floodtide, Hochschild's argument will sound convincing.

But could any of this be important beyond the philosophers' den? Maybe so. One of the most important contributions to modern ecumenical discussion was theologian David Tracy's division of the western Christian world into a camp comfortable with analogy (the Catholics) and a camp prone to what he called dialectical thinking (where the push is to define things always as either black or white with nothing more to say). To the extent Tracy was right, then Joshua Hochschild's careful analysis of Cajetan's recondite defense of analogy late in the 15th century may yet once again challenge Protestants to become more self-conscious about how they speak about God, themselves, and the world in the early 21st century.

Mark Noll is Francis A. McAnaney Professor of History at the University of Notre Dame. He is the author most recently of The New Shape of World Christianity: How American Experience Reflects Global Faith (InterVarsity Press).

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