chapter five

THOMAS AQUINAS

1. Aquinas and the Philosophical Tradition

In passing from to , we come to a break in the historical continuity of the philosophical tradition: not only is Aquinas a Christian, and writing in Latin, but also, whereas was familiar with Par- menides, with Plato and Parmenides, and Plotinus with all three, Aquinas has virtually no direct access to the work of Parmenides, Plato, and Plotinus. His chief philosophical sources, apart from Aristotle, are Augus- tine, , Pseudo-Dionysius, the Liber de Causis, Avicenna, and Aver- roes, and his familiarity with the Platonic tradition is mediated by these and other texts and figures. A history of philosophy would have to discuss all of these sources before coming to Aquinas. Our concern, however, is not primarily textual or historical in nature, e.g., to discuss the influence of the Dionysian corpus and the Liber de Causis on Aquinas’ philosophy, or to trace his doctrine of God as esse, via Boethius and Avicenna, to the Anonymous Commentary on the Parmenides.1 It is, rather, to articulate the strictly philosophical continuity and community between Aquinas’ meta- physics and that of Plotinus. For this reason, we may pass immediately from Plotinus to Aquinas and institute a direct comparison between them. Such a comparison reveals that not merely isolated or peripheral ideas, but the fundamental features of Aquinas’ understanding of being in relation to God as its transcendent principle and source, although often expressed in very different ways, are continuous with the classical tradition as we have seen it developed through Plotinus.2 Consequently, our discussion of

1 On the latter point see Wayne J. Hankey, God in Himself: Aquinas’ Doctrine of God as Expounded in the Summa Theologiae (Oxford: Oxford University Press, 1987), 5–6. 2 For readings of Aquinas that emphasize the Neoplatonic dimensions of his metaphysics see, inter alia, Hankey, God in Himself; Jean-Luc Marion, “Saint Thomas d’Aquin et l’onto- théo-logie,” Revue thomiste 95 (1995), 31–66; Philipp W. Rosemann, Omne ens est aliquid: Introduction à la lecture du ‘système’ philosophique de saint Thomas d’Aquin (Louvain-Paris: Peeters, 1996). Even an anti-Platonic Thomist like Stephen L. Brock, “On Whether Aquinas’s Ipsum Esse is ‘,’” The Review of Metaphysics 60 (2006), 269–270, referring to the 152 chapter five

Aquinas is organized in terms of well-recognized central themes in his meta- physics: the essence-existence distinction; God as ipsum esse; created beings as similitudes of God; analogy of being; the . The aim is to show how, precisely with regard to these most characteristically ‘Thomist’ aspects of his thought, Aquinas’ metaphysics reflects a Neoplatonic vision of reality, which itself unfolded, primarily through Plato and Aristotle, from the Parmenidean principle of the togetherness of thought and being. Such a vision thus constitutes the mainstream of the western philosophical tra- dition, not only in late antiquity and the early Middle Ages, but through the high medieval period in which Aquinas is the principal figure.

2. Essence and Existence

The distinction and composition, within beings, between essence and exis- tence, and the absence of any such distinction or composition in God, is widely recognized as one of the fundamental themes of Aquinas’ meta- physics. Both of these terms, ‘essence’ and ‘existence,’ call for explanation. Aquinas’ use of the term ‘essence’ (essentia) differs slightly from the use of this term as a translation of Aristotle’s phrase τὸ τί ἦν εἶναι. In Aristotle, as we saw, this phrase signifies in effect ‘whatness’ and thus refers to the form of a thing considered without its matter.3 In Aquinas’ usage, the essence of a thing is the answer to the question ‘What is it?’ and therefore includes the matter as well as the form. A sensible thing is neither form alone nor mat- ter alone, but both together, and therefore its essence, or what it is, includes both. “In composite substances4 form and matter is known … But it cannot be said that either of these alone is said to be the essence … For essence is that which is signified by the definition of a thing. But the definition of nat- ural substances contains not only the form but also the matter … It is clear, therefore, that essence includes matter and form” (De ente 1). Matter, consid-

charge of “an infection of ‘platonism’” in Aquinas, remarks, “The complaint, of course, is not simply that (neo)platonic thought is an important source of Thomas’s doctrine of being. For some time now, followers of Thomas have been stressing this very fact. They often use it to help explain why Thomas was able, as they say, to ‘go beyond’ the ontology of Aristotle.” But despite the increasing prevalence of this view in recent decades, Aquinas’ metaphysics is rarely presented as fundamentally Neoplatonic in its most important features. 3 See above, 87. 4 The term ‘substance’ here, translating Latin substantia, is used to refer to a being that ‘subsists,’ that is, exists as a complete being rather than merely as inhering in or as part of some substantial being.