Trinity is the core Christian dogma, but one might not know it from the limited number of works on the subject in late medieval studies (an exception is Russell Friedman's Medieval Trinitarian thought from Aquinas to Ockham, 2010). Either we assume that the matter of God as three persons in one being is settled or, more likely, that it is of less interest than other, less esoteric topics. If the word Trinity is not enough to raise eyebrows, a focus on the metaphysics of ‘divine production’ could cause eyes to glaze over. So we can be grateful to Oxford University Press for publishing this book, if only to help us exercise ‘the little grey cells’.

Scholastic theologians in the late thirteenth and early fourteenth centuries were fascinated by the precise nature of the ‘production’ of the Son and the Spirit. If the Son is begotten by the Father and the Spirit proceeds from the Father (‘from the Father and the Son’ in Western tradition) is this ‘production’ done out of materials or out of nothing? Or is the very idea of production unnecessary, even misleading? Those who took on this challenge faced some enduring dilemmas, especially creation ex nihilo and the subordination of Son and Spirit as lesser deities than the Father.

Completed while the author was a Fellow at the Center for Medieval Philosophy at Georgetown University, this slim but clearly written and often insightful book builds upon the work of Richard Cross (see especially his ‘Duns Scotus on divine substance and the Trinity,’ Medieval Philosophy and Theology xi [2003], 181–201). Paasch concentrates on Henry of Ghent (d. 1293), John Duns Scotus (d. 1308) and William Ockham (d. 1324) ‘because their discussions make up a single conversation’ (pp. 4–5) over roughly a half century and offer a glimpse into the methods of scholastic thinking in the late Middle Ages, including the perennial issues of generation and causation. The general background to this conversation concerned the attempt to balance Augustine (the analogy to memory, intelligence and will) with the powerful impact of Aristotle (the principle that for any x, x cannot be produced out of nothing). In the more immediate foreground loomed the condemnation of Joachim of Fiore by the Fourth Lateran Council in 1215. Joachim (d. 1202) claimed that the Trinity is an intimate relationship of three persons in the same way that many persons are one people and many faithful one Church. The council concluded that Joachim's Trinity was a mere unity by collection.

Opening the dialogue was Henry of Ghent, the influential Parisian theologian whose presence is now beginning to emerge from the long shadow of Thomas Aquinas (see, for example, the new edition of Henry's works by the Catholic University of Leuven). While Henry, Scotus and Ockham agree that the divine essence is the foundation for all divine activity, Henry wants to emphasise relationships among the three persons, and argues that the Father's reproductive activity is similar to how humans build things out of materials. Scotus objected to this apparent materialism, not to mention its subordinationist tendencies. Rather than the divine essence as shared material, the emphasis, he suggested, should be on a shared form that provides the persons with their divine nature. Ockham agreed with Scotus in rejecting Henry's doctrine. The divine essence cannot literally be, nor be like, a lump of matter, but he also rejected Scotus' view. Implying the principle of simplification, Ockham declared that neither the divine essence nor the personal properties need to be asserted as the ‘matter’ or the ‘forms’ of the products because the divine essence cannot come into being through any production at all. It is simply shared with the Son and Spirit; and that's about all we know.

Does this intricate, cerebral interchange among the three participants resolve the questions of subordination and creation ex nihilo? Henry offers the most original suggestion while Ockham comes closest to a satisfactory solution, but the problem may derive from the term ‘production’ itself. If the persons of Son and Spirit are ‘produced’ in any shape or form, it becomes difficult to avoid the criticism that they are created from nothing or are less than the Father. It is often unfair to ask an author to cover some subject that he did not intend, so let it suffice to say that a comparative study of the Trinitarian thought laid out in this volume with Eastern Orthodox approaches could prove to be a salutary supplement.

Technical arguments aside, the author closes with a revealing observation: Scotus and Ockham both accuse Henry of missing the mark, but they do not accuse him of heresy. The key is that, while they may have pushed the envelope, they felt that none had fallen away from the fundamentals of the faith as defined by the Nicene Creed, accepted church doctrine, and the canons of the Fourth Lateran Council. ‘Everything else was up for grabs so to speak and a Christian scholastic was free to make what he could of it’ (p. 195). Persons less familiar with the rich varieties of medieval theological debate may find this openness a refreshing surprise.

Whatever one might think about the utility of Trinitarian metaphysics and the dawn of modern science that gave us acute observation and experimentation, this book attests to the sheer joy of the schoolmen in pure, abstract thought, a joy reflected in the author's sure handling of his presentation.