Home Economics Aquinas’s theory of perception: an analytic reconstruction
The Principles of Intentionality in Aquinas’s Philosophy of Mind
With these preliminary remarks on intentionality theory completed, an elucidation of the principles of intentionality is the next order of business. These principles are developed in a generic manner and are the most general presuppositions necessary for understanding Aquinas’s philosophy of mind. Each principle serves as a presupposition for both Aquinas’s theory of sensation and perception and for his theory of concept formation and exercise. At this rudimentary level of analysis, Aquinas’s account of sense knowledge and intellectual knowledge depends on the same set of principles.
Principle A. An act can only he an act of some ‘X’ or other that has a potency
The potency/act distinction is the central metaphysical principle upon which Aquinas constructs his ontology, his philosophy of mind, and his epistemology. A dominant explanatory principle is not odd in philosophical systems. Commenting on the significance of such principles, Bergmann offered the following insight: ‘In what a great philosopher says there is a pattern. It all flows from one source, a few fundamental ontological ideas. In the light of this source and only in this light, it can all be understood.’ In Aquinas’s ontology and epistemology, the potency/act distinction is what Bergmann would refer to as a ‘fundamental ontological idea’. Aquinas uses this distinction in his ontological account both of the things of the truncated world—except God—and of those cognitive beings capable of intentionality. Hence, this principle applies to Aquinas as both an ontological realist and an epistemological realist. It follows, therefore, that what Veatch called ‘the transcendental turn’ derived from Kantian theory and adopted by many twentieth-century philosophers is structurally distinct from Aquinas’s metaphilosophy.
Neither a potency nor an act has an ontological status by itself; a potency is always a potency of an individual thing, and an act is always an act of an individual thing. The existents in Aquinas’s space-time realist ontology—what one would quantify over— are individual primary substances. Throughout this discussion, therefore, one must remember that things have potencies and acts. Potencies and acts never exist by themselves. The exception is God, who as an Actus Purus (the ‘pure act’) is the only subsist- ent act in Aquinas’s ontology. In his Commentary on Aristotle’s Physics, Aquinas writes: ‘potency and act are the prime division of being’ (III, lec. 2). Using Aristotelian terminology, the analogy here is between matter and form. Form is the perfection, which in some way determines the matter to be what it is. The form is the organizing principle providing the substantial unity of the individual of a natural kind. Thus, an animal body with its multiple types and layers of tissue, fluid, solids, etc. is held together ontologically by the structure of the substantial form. In the Summa Contra Gentiles, Aquinas mentions this analogy: ‘for matter and form are related as potency and act’ (lib. 2 d. 71 n. 2).
In the writings of Thomas, therefore, ‘act’ is neither identical nor coextensive with a ‘mental act’. Rather, it is construed more broadly as any perfection or completion, which anything at all possesses. Act, therefore, is a generic term or concept. It refers to both ontological and epistemological completions or perfections. Some acts are only ontological, while others are also epistemological in nature. Put differently, every epistemological act is an ontological act, but not every ontological act is an epistemological act. An epistemological act has an ontological structure in the mind through which an object is present to the mind in the most general sense. This structure pertains to the ontological nature of a knower, no matter how this might be spelled out. Furthermore, there may be an entity that is unknown by any knower, and thus there would be an instantiation of an ontological act that did not have a corresponding intentional act. It is sufficient for an ontological act that it is epistemological in nature, but it is not necessary that an ontological act be an epistemological act. In effect, this distinction renders idealism impossible in the ontology of Aquinas. This is another instance indicating that Aquinas is an ontological realist and an externalist.
Moreover, act is to be understood in two additional senses. First of all, there is the actual state or capacity of an existent. Act as state or capacity is best defined as a dispositional property. This distinction applies to both ontological and epistemological acts. In Aquinas’s ontology, a substantial form, for instance, is best understood as the ontological ground for a set of dispositional properties. This distinction between disposition and exercise is especially important in discussing Aquinas’s philosophy of mind. A discussion of concepts-as-dispositions and concepts-as-being-exercised in acts of knowing is central to his philosophy of mind. Briefly put, a concept, as an acquired epistemological or intentional disposition, would be Marianne’s ability to read French. Yet this concept as an acquired epistemological disposition is only ‘exercised’ when in fact Marianne is here and now reading French. At the moment, Marianne may be reading Dilbert’s Principles of Management, but when she is reading about Dilbert’s escapades with Dogbert, she has not lost her ability to read French. In Aquinas’s Commentary on Aristotle’s On the Soul this distinction is discussed:
And as a receiver is to what it receives, a potency is to its act. And as act is the perfection of what is potential, so being acted upon in this sense implies rather that a certain preservation and perfection of a thing in potency is received from an object in act. For only the actual can perfect the potential, and actuality is not, as such, contrary to potency. . . . (Commentary on the Soul, #366)
In effect, Principle A asserts that in Aquinas’s ontology, there are no ‘free-floating’ acts. Rather, each and every perfection is a perfection of something or other. Put differently, Principle A is a fundamental principle of Aristotelian hylomorphism. Each individual thing in the world is a compound of two principles: matter, which is by definition a potency; and form, which is by definition an act. The Commentary on the Soul
illustrates this claim: ‘Matter, then, differs from form, in this, that it is a potential being. Form is the “entelechy” or the act that renders matter actual. The compound is a resulting being (a particular primary substance)’ (Commentary on the Soul, no. 215). Because God is the only exception to this Principle, it follows that God as an Actus Purus in effect becomes the only ‘free-floating’ act in Aquinas’s ontology.
In his study of Aquinas on human nature, Pasnau argues correctly that there is a ‘deep metaphysics’ that lies implicit in Aquinas’s ontology, especially his account of human nature. The ontological theory of ‘actuality’—or ‘act’ as used in this book—is central to Aquinas’s account of real beings. Pasnau writes that ‘actuality is explanatorily basic because it is metaphysically basic, because there is simply nothing else that might figure into an explanation’.
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