Home Economics Aquinas’s theory of perception: an analytic reconstruction
The Incidental Object of Sense and the Vis Cogitativa
Having argued that both the common and the proper sensibles are Sensation-Ia objects, Aquinas next embarks on a discussion concerning how these objects—Sensation-Ia objects—differ from the incidental object of sensation, which is a Sensation-Ib object.
Having seen how we should speak of the absolute or essential sense objects, both common and special [proper], it remains to be seen how anything is a sense object ‘incidentally’. Now for an object to be a sense object incidentally: (a) it must first be connected accidentally with an essential sense object; as a human person, for instance, may happen to be white, or a white thing may happen to be sweet. Secondly, (b) the one who is sensing must perceive it; if it were connected with the sense object but not itself being perceived, then it could not be said to be sensed incidentally. But this implies that with respect to some cognitive faculty of the one sensing it, it is known, not incidentally, but absolutely. Now this latter faculty must be either another sense faculty, or the intellect, or the cogitative faculty, or natural instinct. I submit that it must be another sense faculty, meaning that sweetness is incidentally visible inasmuch as a white thing seen is in fact sweet, the sweetness being directly perceptible by another sense, i.e. taste. (Commentary on the Soul, no. 395)
The vis cogitativa will be discussed here only briefly; a later chapter provides a thorough analysis of this important inner sense faculty. Nonetheless, whenever an object is sensed, it follows that there must be a faculty by which the perceiver is directly related to that object. Human perceivers have the faculty of sight in order to be aware of colour, and so on for the rest of the proper sensibles. Aquinas realizes that one pre-analytic datum of ordinary experience is that at times a human perceiver is aware of an individual person or thing precisely as that individual person or thing, and not as a colour patch or shaped object or any mere Berkeleyan bundle of sensations. Philosophers like Chisholm, among others, referred to this pre-analytic datum as ‘thing consciousness’. In Aquinas’s philosophy of mind, if the above data of experience is to be analysed—and he is convinced that human perceivers are directly aware of individuals as individual things—then he is committed structurally to postulating a separate sense faculty in order to account for this different type or species of awareness. This is another example of Aquinas’s instantiation of Principle C from Chapter 2—A potency of any ‘X’ must be specified or properly disposed in order to receive any given act’—suggesting that a disposition is related directly to an act. In the present case, the act is the awareness of an individual as an individual thing. This act needs a requisite disposition or sense power, which Aquinas calls the vis cogitativa.
In effect, as will become evident in the following texts, Aquinas proposes that the vis cogitativa is that faculty or cognitive disposition or power by which a perceiver is directly aware of an individual as an individual thing—e.g. the son of Diares as such. Diares would be an instance of a primary substance in Aquinas’s ontology. ‘If this apprehension is of something individual, as when seeing this particular coloured thing, I perceive this particular human person or particular beast, then the cogitative faculty (in the case of human knowers, at least) is at work, the power that is also called the “particular reason” because it correlates individualized awarenesses just as the “universal reason” correlates universal ideas’ (Commentary on the Soul, no. 396). In brief, the vis cogitativa is that faculty of the internal sensorium by means of which a perceiver is directly aware of an individual precisely as an individual. Nonetheless, even in a preliminary way the vis cogitativa appears to have two functions: the recognition of an individual as an individual thing; and the recognition of an individual as a member of a certain natural kind. A fuller analysis comes later in this book. Aquinas argues that the mental act of the vis cogitativa enables a distinction to be made between the sensation of Sensation-la objects and perception of Sensation-lb primary substances. The vis cogitativa through an internal cognitive structure permits an individual primary substance to be perceived as such an individual and not merely as a collection or bundle of sensations. Like Thomas Reid, Aquinas gets beyond Hume’s psychological atomism.
Now that the objects of sensation have been discussed, the next chapter begins the explication of the acts of awareness appropriate to sensation. This is a further instance of Aquinas’s teleology—the object determines the act, and the act determines the faculty. This analysis is similar to that proposed by ecological naturalists like Gibson, who suggest that human perceptual abilities developed in order to assist human perceivers make their way successfully around the environment. There is a similarity in conclusions between Aquinas and Gibson. This is not a claim of isomorphism of arguments, however, but rather a roadmap pointing to a form of cognitive naturalism found in both scholars developing a position on sensation and perception.
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