Home Economics Aquinas’s theory of perception: an analytic reconstruction
The Sensus Communis and the Phantasm
One additional point needs clarification before completing this expository analysis of the sensus communis. Several commentators on Aquinas’s theory of perception have argued that a phantasm is needed in order for the sensus communis to function. In his Sensation and Perception, Hamlyn offers this interpretation:
Aquinas believes, therefore, that corresponding to the physical change in the sense organ, there is a spiritual change resulting in a phantasma, which is a particular mental entity. [. . .] On the Thomist view the phantasmata set up are mental entities and for this reason are like sensations which are produced by stimulation of our bodily organs; yet, being somehow representative of 
the objects which produce them, they are more than mere sensations. They are indeed more like the ideas or impressions of the British Empiricists, Locke, Berkeley and Hume, except that Aquinas holds that we are not ordinarily aware of them.
Weinberg wrote much the same thing:
An object external to the human organism causes the medium between the object and the sense organ to have duplicates of the forms of the object. In turn, the medium communicates forms to the sense organs and thence to the faculties of sense. These various forms thus received are brought together (by the internal senses) into a common image or phantasm.
What these two passages imply is that the awareness of a ‘complete whole’ by the sensus communis is accomplished by means of a phantasm. In one of his books on Aquinas, Pasnau (along with Kemp) also suggest this role for the phantasm. In other words, the ‘conjunction’ of discrete sensibles accomplished by the sensus communis produces a phantasm, which is the object of the act of awareness of the sensus communis itself. In effect, the claim put forward is that the sensus communis has for the object of its mental act a phantasm. In this chapter, the present purpose is not to elucidate the concept of phantasm. However, several commentators have construed the phantasm as involved in direct perception involving the external senses. The conclusion of the analysis illustrated by Hamlyn and Weinberg is that either a phantasm is produced in all of the external senses or else is the ‘synthesis’ produced by the sensus communis from the discrete data from the external senses. In other words, the phantasm is the direct object of the mental act of sensation. This would entail that the phantasm as an image is the direct object of perception.
This position still holds sway in discussions of Aquinas on perception. Several recent commentators on Aquinas’s theory of perception argue that a phantasm, what they take to be an image, is an intermediary intentional entity that serves as a necessary condition for perceiving things in the external world. This entails that Aquinas is a representationalist in his theory of perception. Pasnau too is unclear on the role of phantasm in Aquinas’s philosophy of mind. In Thomas Aquinas on Human Nature, Pasnau adopts a position similar to what will be discussed later in this book, although his account is not as detailed. In his translation of A Commentary on Aristotle’s De Anima, nonetheless, Pasnau offers a more restrictive picture. In this latter book, he writes that ‘phantasms, for Aquinas, are the images or representations produced by phantasia (imagination)’. In his extensive commentary on Aquinas’s theory of human nature, moreover, Pasnau appears to adopt the opposite position. In an illustration of the internal senses, Pasnau holds that phantasms belong to the sensus communis.30 In a review of Kemp’s Cognitive Psychology in the Middle Ages, Pasnau wrote: ‘According to Kemp, it was the standard medieval view that the common sense is responsible for imagining images (as opposed to storing them). This is an important issue, and I think Kemp gets it right.’31
On the contrary, however, Aquinas never uses the term ‘phantasm’ when discussing either direct sensation involving only the external senses or any mental act involving the sensus communis. Of course, if the sensus communis has an image for its direct object, this renders Aristotelian philosophers representationalists, thus subverting the epistemological realist thrust of much Aristotelian perception theory, especially that elucidated by Aquinas. Kemp and Pasnau are not the only ones who hold this position. In opposition to what might be called the Kemp-Sometime Pasnau interpretation, Aquinas mentions explicitly the powers or sense faculties in which the phantasm is found, and this listing conspicuously omits any discussion of the sensus communis. The Summa Contra Gentiles indicates this position: ‘The powers in which the phantasms are found, namely, the imagination, the memory and the vis cogitativa’ (Summa Contra Gentiles, bk II, ch. 73, 11).32
Other passages in Aquinas’s texts indicate this same point. In these texts, Aquinas discusses the internal sense powers in which the phantasms reside. It would be inconsistent were he to omit any mention of the sensus communis if a phantasm did ‘reside’ with this internal sense faculty. In addition, there appears to be no passage in which he discusses explicitly phantasms as belonging to the sensus communis.33 On the other hand, there are many places where Aquinas asserts that the phantasms are found only in the other three internal sense faculties, conspicuously omitting any reference to the sensus communis.34 It is a serious misreading of the Aquinas texts to have any image in the sensus communis, especially a phantasm. It is possible that historians of philosophy like Hamlyn and Weinberg confused the ‘sensible species’ with the phantasm. These two concepts, however, are neither identical nor     
coextensive. Kenny notes that in discussing phantasms, ‘this theory seems to be confused in several ways’.
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