Home Economics Aquinas’s theory of perception: an analytic reconstruction
The Act/Object Distinction
In considering Aquinas on intentionality, one needs to recall Aristotle’s conception of the act/object distinction. In the Metaphysics, this distinction is central to Aristotelian intentionality theory, which also indicates his realism and externalism: ‘But it is clear that knowledge, perception, opinion and understanding always have some object other than themselves. They are only incidentally their own objects. [. . .] “Thinking” and “being thought of” are different. [. . .] For the essences of “thinking” and “being thought of” are not the same’ (Metaphysics, bk XII, ch. 9).
The text just considered illustrates the importance of the act/object distinction. Insofar as the object is distinct from the mental act, this suggests the need for a connection between the mental act and the object known. This connection is analysed in terms of a property of ‘tending towards, which in turn is grounded in the unique characteristic of the immaterial dispositions providing for the ontological possibility of intentionality. This is the root analysis explaining the possibility of knowing provided in Aquinas’s philosophy of mind. This distinction reiterates the claim, not surprisingly, that in the Aristotelian-Aquinian philosophy of mind, idealism is false. Aquinas is an ontological realist to the core.
The philosophical weight of combined passages and, a fortiori, of Principle D-1 itself is that a knower, when it takes on or exemplifies the form of an object in the external world, does not itself literally and physically become the object as it is in the material world. This principle and its elucidation in terms of an immaterial manner of becoming are necessary conditions for an analysis of Aquinas’s thesis of intentionality. Were it not for a knower’s possessing the unique set of dispositional, cognitive properties capable of being actualized and activated by the form of an object without literally becoming that object entitatively, then, it could be argued, Aquinas could not explain the possibility of knowledge. Given the Aquinian ontology in terms of hylomor- phism, the possibility of esse intentionale, and a fortiori of discussions in the philosophy of mind, would be removed a priori. This indicates once again the ontological dimension to Aquinas’s theory of intentionality. A natural entity existing in the external world is there only because it has esse naturale. An act of awareness in a knower is there only because this act of awareness is of an object that possesses esse intentionale in a knower. Hence, in Aquinas’s system, there are two kinds of existence that a thing might possess: things that exist naturally outside of the mind’s awareness and things that have the ontological capacity to have acts of awareness; and when an act of awareness of an object is in a knower, this is an exemplification of an esse intentionale. Hence there are two categories of the act of existence—natural existence and intentional existence. A knower has the capacity to have an intentional existence of an object. This is the root foundation of Aquinas’s philosophy of mind. While it is similar structurally to the insights of Brentano, nonetheless it is rooted in the ontological possibility of a being undertaking acts of mental awareness. Hence, what Aquinas proposes is close to Chisholm’s account of intentionality, and removed from the classical phenomenolo- gist attempt at ‘pure description’ of mental acts of awareness.
The purpose of indicating other sources like Descartes, Brentano, Husserl, and Chisholm in this analysis of Aquinas’s philosophy of mind is not to suggest that all five philosophers entertained identical intentionality theories. Certainly they did not. Rather it suggests that Aquinas’s method in discussing an ‘immaterial reception of forms’ is not as odd epistemologically as one might at first glance suspect. In effect, Aquinas’s account is akin structurally to any philosophy-of-mind discussion in terms of the general characteristics of an ontologically based intentionality theory. It is connected less with contemporary intentionality theories suggesting that propositional attitudes are sufficient conditions for an analysis of intentionality. Needless to say, among philosophers there are specific differences regarding various accounts on intentionality. As an epistemologist considering intentionality, Aquinas attempts to provide an ontological analysis and explanation of what it means to be a knower. His explanation of this primitive datum of human experience is through the notion of ‘having a form in an immaterial manner’. By this account, Aquinas believes that he offers an analysis of why, when a knower is aware of ‘red’ or ‘horse’, this knower, although receiving a form, nevertheless does not become another red object or another horse in the world. If this immaterial reception of forms were not the case, assuming the hylomorphism of Aquinas’s ontology, it would follow that every contact of an act on a potency would produce another object or quality in the external world. Accordingly, there would be no possibility of explaining the pre-analytic datum of knowledge. Obviously Aquinas’s account is couched within a framework of Aristotelian hylomorphism. Furthermore, this explanation is in concert with an earlier claim that Aquinas’s philosophy of mind follows from his ontological account of primary substances. If a primary substance is an ontological conjoining of matter and both substantial and incidental forms, then Aquinas’s intentionality thesis explains how these two forms as ontological structures of reality are known. This explains how Thomas accounts for the possibility of knowing a primary substance and its incidental properties. In his On the Unity of the Intellect Against the Averroists, Aquinas elaborates on this point: ‘If there were some colour within the pupil, that inside colour would make it impossible for an outside colour to be seen, and in some way would prevent the eye from seeing other things’ (ch. 1, sect. 20).
This principle describing the immaterial reception of forms as the basis of an inten- tionality thesis is, therefore, the central principle in Aquinas’s philosophy of mind. The denial of Principle D-1 entails the abolition of the distinction between esse naturale and esse intentionale. Furthermore, the principle of immaterial reception of forms is objectiva): ‘This truth is not only clear and evident in regard to the effects which philosophers call actual or formal reality, but also in regard to the ideas where one considers only what they call objective reality’: See Meditation III. While textual criticism revolves around Descartes’s use of realitas objectiva, nonetheless in the Third Meditation his use of the term seems conceptually similar to what Aquinas meant in discussing intentionality. When Brentano wrote about the distinction between the ‘class of physical and the class of mental phenomena’ he provided his own analysis of this distinction. Moreover, Husserl suggested that Brentano ‘presented to the modern era the idea of intentionality’.
the basis for the isomorphism between the form in the mind and the form in the world. Ultimately, this isomorphism is the structural ground for the possibility of veridical, objective knowledge. Concerning the necessity of isomorphism in order to ground the very possibility of knowledge, Sellars once set out the following principle, one with which Aquinas would agree: ‘I believe it must be granted that unless the sensation of a white, triangular thing were in some way isomorphic with its external cause, knowledge of the physical world would be impossible.’ Within Aquinas’s metaphysics, therefore, a denial of Principle D-1 entails the a priori impossibility of knowledge. The realism is evident, and there are no lingering shadows of postmodernism. By his theory of forms, Aquinas articulates the possibility for an epistemological realism and an ontological realism, both of which are rooted in his externalism.
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