Otherness, Plurality and Numerical Individuation in Aquinas’s Super Boetium de Trinitate

In this paper I grapple with part 2, question 4 of Aquinas’s commentary on Boethius’s De Trinitate, in order to shed light on understudied textual passages, and to offer an original account of Aquinas’s view of individuation and its relationship to Boethius’s. I focus in particular on his account of Boethius’s claim that otherness is the cause of plurality. I argue that Aquinas definitively overcomes some Neoplatonic elements of Porphyry’s view, which Boethius’s understanding of alteritas still retained. In section one, I provide some introductory elements on the theological, metaphysical and logical issue at stake in Boethius’s De Trinitate, as well as in Aquinas’s commentary. In section two, I introduce what I call the ‘individual form problem’ and endeavour to show how it relates to the remote dialogue between Boethius and Aquinas and, via Boethius, between Porphyry and Aquinas. In section three, I deal more specifically with Porphyry’s model, and with the twofold metaphysical tenet I call the ‘D-E principle’. In section four, I briefly discuss Boethius’s account of otherness, plurality, and individuality, with a special focus on his relationship to Porphyry. In section five, I discuss Aquinas’s own solution by stressing the philosophical significance of his account, and considering the ways in which he departs from Boethius and Porphyry on these points. I also delve into the connections between his account of essential otherness and its involvement in the composition of individual substances, by comparing the opposite cases of angelic and hylomorphic individuations. In section six, I offer some brief concluding remarks.