Home Economics Aquinas’s theory of perception: an analytic reconstruction
The Ventricle System and Aquinas’s Cognitive Theory of Inner Sense
Kemp falters, it appears, in his analysis of Aquinas on the internal sense faculties. Textual support provides evidence that Avicenna argued for five internal sense faculties where Aquinas only postulated four. Avicenna divided the imaginatio into the retentive imagination and the compositive imagination, or what he referred to as the vis cogitativa.49 The former was the ‘storehouse’—the ‘thesaurus’ in Aquinas’s Summa Theologiae account—while the later was the faculty that produced images like ‘the golden mountain. Aquinas sees no need to divide these two aspects of the imaginatio and hence postulates only one inner sense faculty that is capable of two functions. Moreover, the vis cogitativa for Thomas had a different function.
Kemp’s consideration of the sensus communis, and his claim that Aquinas postulates the vis aestimativa as a human faculty of inner sense, are not four-square with the texts. At this juncture, Kemp, like many historians of both philosophy and psychology, adopts a paradigm of explanation from epistemological theories as developed in modern philosophy. Kemp appears to assume that Aquinas—and several other medieval Aristotelians—defend a representational view of perception. Following this interpretive method, historians of psychology like Kemp and Thomas Leahey go awry in their structural accounts of Aquinas on the internal senses.
Where Kemp goes astray in his account is his suggestion that the resultant combination of discrete external sensibles produces an ‘image’ known by the sensus communis. Kemp writes: ‘The images produced in the common sense are stored in the imagination (Latin: imaginatio or formans) located at the back of the front ventricle.’  He also writes that ‘in normal waking life the images that are presented to the common sense [. . . ] arise from perceiving the world’.  Kemp refers several times to ‘images in the common sense’. This would entail that Aquinas is a representationalist in his theory of perception.
There is another textual blur in Kemp’s analysis of Aquinas. Kemp has the vis cogitativa as the cognitive faculty in animals responsible for the performance of complex functions, like the spider weaving its web or the bird building its nest. Aquinas gives these cognitive functions to the vis aestimativa, which he sometimes characterizes as instinct in animals; however, it is not found as a cognitive inner sense faculty in human persons. In his Cognitive Psychology in the Middle Ages, Kemp suggests that Aquinas and Avicenna differ in that Aquinas denied the existence of the vis cogitativa. Even a cursory glance at almost any set of Aquinas texts on inner sense demonstrates that Kemp’s claim is incorrect. Leahey, moreover, also ascribes what he refers to as ‘estimation’ to the human perceiver. Yet he also refers to ‘human estimation’ as the ‘cogitativa’.53 Furthermore, in the Summa Theologiae, Aquinas argues that it is in the imaginatio where the composite image of the ‘golden mountain’ is formed, not, as Kemp suggests, in the vis cogitativa.
On the other hand, Kemp suggests, rightly, that the vis aestimativa is, according to Avicenna—and also Aquinas—the inner sense faculty ‘which perceives the non-sensible intentions that exist in the individual sensible objects, like the faculty which judges that the wolf is to be avoided. These are, Avicenna writes, ‘intentions which we do not sense’ Aquinas argues in his Commentary on Aristotle’s On the Soul that the vis cogitativa (and the vis aestimativa in animals) provides the cognitive ability to be aware of non-sensible forms—the so-called ‘intentiones non sensatae’. The intentional object of the vis cogitativa is what Aquinas refers to as the Aristotelian ‘incidental object of sense. This faculty of inner sense renders possible his awareness of the individual as a primary substance and not merely as the ‘bundle of sensations’ so common to British empiricism. For Aquinas, part of the function of the vis aestimativa in animals is absorbed in humans, as it were, in the inner sense faculty of the vis cogitativa. Hence, the human perceiver does not have a vis aestimativa but an enriched vis cogitativa. In considering the inner sense faculties, Kemp notes that Roger Bacon called the vis cogitativa ‘the mistress of the sensitive faculties’. This indicates the dignity of this important inner sense faculty, one that has been seriously neglected in much contemporary commentary on Aquinas’s theory of sensation and perception.
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