The title of Irena Backus’s Leibniz: Protestant Theologian is apt to strike readers as incongruous given that, by her own admission, “Leibniz never pretended to the status of a theologian” (63; see also 74). Nevertheless, he did write extensively on religious matters and developed a number of original religious views, some of which are the focus of this book, which seeks to throw light on Leibniz as a religious thinker, especially as regards his doctrines of the Eucharist and predestination. The book contains seven chapters split into three parts. Part 1, “Eucharist and Substance,” consists of two chapters that examine Leibniz’s understanding of the Eucharist and the doctrine of substance in key texts from 1668, 1686, 1697–98, and 1712, thus charting the development of his thinking of the metaphysics of transubstantiation. Part 2, “Predestination and Necessity,” contains three chapters, one on Leibniz’s doctrine of predestination, one on his doctrine of necessity, and one on his use of Augustine. Part 3, “Leibniz, the Historian of the Sacred,” contains two chapters that examine Leibniz’s thinking on sacred history and prophecy, respectively.

At the start of the book, Backus states that she is a religious historian rather than a philosopher and that her book is aimed at historians of ideas, theologians, and historians of religion. Accordingly, her aim is to situate Leibniz’s religious thought in his intellectual context by detailing “the historical links between the questions he asks and those asked by his contemporaries” (2). While it is clear that Backus does not see the book as a work of philosophy, her choice of topics makes it difficult for her to avoid entering into Leibniz’s philosophical views, which in fact are front and center for a good part of the book. Unfortunately, in her handling of Leibniz’s philosophy there is much to make Leibniz scholars wince. In chapter 3, for example, she glosses Leibniz’s notion of free will as involving “the will to will” (84), even though there are many texts in which Leibniz explicitly states that such a notion is incoherent because it involves infinite regress (e.g., “We will to act, strictly speaking, and we do not will to will; else we could still say that we will to have the will to will, and that would go on to infinity”: Leibniz, Theodicy [1985], 151). Later, Backus states that Leibniz appears to establish a clear distinction between necessity and certainty “very late in his career” (107), citing a text from 1711 as evidence of this. Yet there are much earlier texts in which Leibniz makes a clear distinction between necessity and certainty, such as one from 1680–84 (in Shorter Leibniz Texts [2006], 107).

Overshadowing Backus’s apparent unawareness of relevant primary sources is her neglect of relevant secondary sources. For example, when outlining Leibniz’s doctrine of substance early on (14), Backus places texts from 1668 and 1714 side by side and takes them to be expressing the same view of the soul as the form of the body, thereby disregarding decades of Leibniz scholarship that has carefully sought to show an evolution in Leibniz’s thinking about substance. To compound matters, Backus engages with only a selection of the relevant secondary literature on the topics covered by her book, with virtually no engagement with leading scholars such as Maria Rosa Antognazza, Daniel J. Cook, and Michael Murray. This leaves the reader unclear if or when Backus is (or takes herself to be) offering new lines of interpretation of Leibniz’s thinking.

Not surprisingly, given that Backus is a religious historian, she is on much firmer ground when handling theological matters and in particular when detailing the interplay of ideas of various key religious figures, especially those of the Reformed. And indeed, where Backus excels is in laying out the theological context for some of Leibniz’s forays into theology, showing the depth, subtlety, and nuances of the various positions that had been developed in the sixteenth and seventeenth centuries, as well as Leibniz’s knowledge thereof. The chief value of this work thus consists in the way it successfully situates some of Leibniz’s religious views in their appropriate historical and theological context.