Gracia and Aquinas on The Principle of Individuation

The Thomist 68 (2004): 545-75 GRACIA AND AQUINAS ON THE PRINCIPLE OF INDIVIDUATION ANDREW PAYNE St. Joseph's University Philadelphia, Pennsylvania IN RECENTYEARS Jorge Gracia has developed a nuanced and sophisticated account of the nature of individuality and of the principle of individuation. He has developed this view in part by criticizing the standard Thomistic account of the principle of individuation as dimensive quantity. The present essay seeks to rehabilitate dimensive quantity by arguing against Gracia that, rightly understood, it does explain the individuation of material substances. This requires a two-part strategy. First, the meaning of dimensive quantity must be recovered by examining the roots of this concept in Aristotle's Categories and Physics. The standard Thomistic presentation of dimensive quantity in the writings of Joseph Owens and Joseph Bobik is vulnerable to objections raised by Gracia, and this makes necessary a review of selected passages from Aristotle dealing with quantity. In particular, the notion of position contained in these texts must be elaborated in order to grasp the distinctive content of the concept of dimensive quantity. Second, Gracia's objections to the Thomistic principle of individuation must be considered in light of this fuller understanding of dimensive quantity. It will be seen that these objections are not compelling, and that dimensive quantity provides a satisfactory principle of individuation for material substances. In particular, Aquinas's discussion of numerical difference in his commentary on Boethius's De Trinitate will be 545 546 ANDREW PAYNE defended. The upshot of these passages is that matter marked by quantity and position will occupy a determinate place, whereas two distinct material substances cannot occupy the same place simultaneously. As aresult, matter modifiedby dimensive quantity is assigned to some determinate place and time, which suffices to individuate material substances. To limit the scope of this project, I will defend dimensive quantity only as a principle of individuation for bodies or material substances. In Scholastic usage, these are composite substances, those constituted by the union of form and matter. Gracia rejects dimensive quantity as a principle of individuation in part because it cannot serve as a universal principle of individuation-that is, one that could individuate nonmaterial substances such as angels, God, Cartesian souls, abstract entities, etc.1 According to Gracia, it is the existence of each thing that is its principle of individuation. For now I wish to put to one side the question of whether we should look for a global principle of individuation, as Gracia does, or attempt instead to find different principles of individuation suited to different kinds of entities, although my strong preference is for the latter option.2 I will focus instead on whether dimensive quantity provides a satisfactory principle of individuation for material substances. Furthermore, I will make no attempt to present the full teaching of Aquinas on dimensive quantity based on an historical survey of his writings. As commentators have noted, Aquinas seems to change his mind or at least express his mind differently over 1 See Jorge Gracia, Individuality: An :Essay on the Foundations ofMetaphysics (Albany, N.Y.: State University ofNewYork Press, 1988), 155. Other works in which Gracia develops his account of individuation are Suarez on Individuation, ed. Jorge Gracia (Milwaukee: Marquette University Press, 1982); "Individuals as Instances," Review of Metaphysics 37 (1983): 39-59; and "Introduction: The Problem of Individuation" in Individuation in Scholasticism: The Later Middle Ages and the Counter-Reformation (1150-1650) ed. Jorge Gracia (Albany, N.Y.: State University of NewYork Press, 1994), 1-20. 2 This approach is taken by Lawrence Dewan, who speaks of individuality in Aquinas's thought as a mode of being, where being is said in many ways. He sees in Aquinas a global approach to the individual butnota single global principle ofindividuation, in light of the fact that "in diverse levels of being there are diverse 'principles' of individuation" (Lawrence Dewan, 0. P., "The Individual as a Mode of Being According to Thomas Aquinas," The Thomist 63 [1999]: 424). THE PRINCIPLE OF INDMDUATION 547 the course of his career when writing about the principle of individuation.3 I have focused on the E.xpositio superlibrum Boetii De Trinitate, not because it contains the whole...