L'essentialisme de Guillaume d'Ockham by Magali Roques (review)

In this short but dense monograph, Roques sets out to fill a significant lacuna in the literature on William of Ockham's logic, epistemology, and metaphysics: his theory of real definitions. Remarkably, the subject has received little attention, given that nominal definitions, specifically in connection to complex connotative concepts in mental language and their role in Ockham's ontological reductionism, have been a central focus since the early 1980s. One reason for this oversight may be the historical association between real definitions and the realist view that essences are universal entities. Ockham, a resemblance nominalist, holds that all essences are individual entities; this does not, as Roques's present work attests, entail any anti-essentialism on his part.

Substances, since Aristotle, have been understood to have essences and are, therefore, definable by real definitions that express the necessary properties predicable of those substances. Roques's guiding question is: is Ockham's theory of real definitions essentialist? Outlining various ways that medievalists and contemporary analytic philosophers have conceived of essentialism (she quickly discounts medievalists' "equivocal" use of the term), she focuses on Quine's description of Aristotelian essentialism as the thesis that certain necessary properties exist independently of the way we name or conceive them. What follows is a detailed, comprehensive analysis of real definitions in Ockham's thought.

Opening the central section of the book, the second chapter considers the semantics of real definitions. Roques gives a close reading of an under-discussed text, distinction 8 of the Ordinatio, that examines various semantic features of genus terms ("animal") and difference terms ("rational"), which, if formed into complex mental concepts or expressions, make up real definitions ("rational animal"). It emerges that a complete real definition explicates all the essential parts of the substance defined, confirming that only substances composed of matter and form(s) are definable. She ends with the suggestive but unelaborated claim that Ockham's criterion of ontological commitment could be fulfilled by the set of propositions in which definitions, real or nominal, are adequately predicated of their definienda.

The third chapter is dedicated to an epistemology of real definitions. A primary interest here is to determine how we come to evidently cognize propositions in which real definitions are predicated of their definienda ("every human being is a rational animal"). Because Ockham thinks that these propositions are only discoverable by experience, whether this is in fact possible for human cognizers in this earthly life, she argues that they are analytic and contingent truths that are nonetheless a posteriori. She also discusses the status of real definitions in the production of scientific knowledge of natural substances.

The fourth and final chapter explores the metaphysics of essences or quiddities, which, for Roques, ultimately amounts to an analysis of Ockham's reductionist thesis on the mereological structure of composite substances. The essence of a composite substance is identical to its essential parts, its matter and form(s), at least when those parts are naturally unified and in the same place despite the logical or metaphysical possibility that God separate them.

In a condensed conclusion, Roques finally returns to Quine, convincingly arguing that Ockham's theory of real definitions is essentialist. Substances, or essences, have necessary properties irrespective of our naming or conceiving. If the existing Socrates is a man, he is necessarily a man, a rational animal. All too rapidly, she admits, she compares Ockham's essentialism to Kripke's (all necessary properties are essential) and Kit Fine's (every essential property is necessary, but not every necessary property is essential) without decisively aligning him with one over the other.

The book is well-written in lucid French. Her target audience, however, is specialists. Non-experts will encounter technical but crucial terminology that she does not explain ("supposition" and "adequate object of the intellect") or explains later than one would expect ("connotation"). While she clearly and readily detects compelling philosophical connections, she often refrains from...