Home Economics Aquinas’s theory of perception: an analytic reconstruction
Sensation as a Generic Term
In Aquinas’s texts, sensation is a generic term, which can be referred to as ‘Sensation-I’. The intentional characteristics of the acts of awareness of Sensation-I are all an awareness of the objects of the external world, i.e. incidental qualities of the particular concreta or primary substances in which the incidental properties inhere. Sensation-I is not connected with the awareness of essences or universals—i.e. either first-intention concept formation and exercise or second-intention universal formation; sensation-I is never reducible to intellectual knowledge. However, there are two types of Sensation-I mental act, and each type of Sensation-I is a direct awareness aligned in some way with the external senses and with specific objects. The sense objects will be the directly perceivable objects, which also might be termed ‘Objects of Sensation-Ia. These objects are the proper and the common sensibles. The second type of Sensation-I is the mental act of the internal sensorium faculty of the vis cogitativa. This is the mental awareness that has for its object the indirectly perceivable; these might be termed ‘Objects of Sensation-Ib. This class of Sensation-Ib obj ects is determined by phantasms through the mental act of the vis cogitativa.
Structurally, the objects of Sensation-Ia—the directly perceivable objects—are known only by the external senses. Accordingly, it is the objects of Sensation-Ia which are the objects of direct sensation. The objects of Sensation-Ib—the indirectly perceivable objects—are known only through the workings of an internal sense. Yet both types of awareness are in some way awareness of particular qualities or things which exist in the external world. It is for this reason that the term ‘Sensation-I’ has been introduced as a generic notion which has subsumed under it Sensation-Ia—direct sensation with the external senses—and Sensation-Ib—perception by means of the internal sense of the vis cogitativa. It is important to realize that there is no role for inference with Sensation-Ib awareness. Aquinas does not use an inferential process to account for Sensation-Ib mental acts and objects. The indirectly perceivable object in Aquinas is neither identical nor coextensive with what many twentieth-century philosophers called the indirectly perceivable object. Furthermore, contrary to Michon, Aquinas does not appeal to any ‘inference’ in discussing how the incidental object of sense is perceived.
Comments from several twentieth-century philosophers are useful in considering how Aquinas’s philosophy of mind might play out in contemporary discussions. Aquinas’s Sensation-Ib object reminds one, as Kerr writes, of both Putnam’s and McDowell’s claims that there is no need to ‘bridge the supposed gap between mind and world [ . . . because] there is no such gap—though much effort needs to go into liberating philosophers from assuming that there is’. For Aquinas, the object of a mental act is an ‘aliquid extraneum, which instantiates the externalist thesis. McDowell comments: ‘We need to stand firm on the idea that the structure of elements that constitute a thought, and the structure of elements that constitute something that is the case can be the very same thing.’ Haldane notes that McDowell’s claim ‘is as close as makes no substantive difference to the old orthodoxy of Thomist metaphysical realism’. Kerr comments on Putnam’s recent work:
Over the years, especially recently, Putnam has been working towards what he now calls ‘natural realism’, the truth that we do, after all, perceive the world directly. Thomas can be enlisted as an ally in the struggle, which is still central in modern philosophy, to liberate philosophers from the notion that the knower can have nothing better than indirect knowledge of anything, which means (in Kantian terms) that the world is as it appears may not be the world as it really is—at least for all we know. Putnam is now quite happy to agree that ‘Aristotelian realism’ is very much what he wants.
Sensation-Ia objects, accordingly, are the objects of what one normally calls sensation. Sensation-Ib objects using the vis cogitativa are the objects of what one calls perception. The objects of sensation are the proper and the common sensibles. These properties are analogous with but not reducible to the primary and secondary qualities of the British empiricists. The obj ect of perception is the incidental obj ect of sense, which is the individual primary substance—the individual thing or concretum—in Aquinas’s metaphysics. There is no analogue for the incidental object of sense in mainstream British empiricism nor, until recently, in much twentieth-century analytic philosophy of mind.
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