Direct Realism in Aquinas’s Theory of Sensation
A further corollary to the present set of claims concerns the status of that difficult concept in Aquinas’s theory of sensation and perception, the phantasm. ‘Phantasm’ is a much-used and much-abused epistemological concept found in Aquinas. The phantasm is identified neither with the sensible species nor with what the scholastic commentators called the ‘species impressa’. It is a category mistake, therefore, to link ‘sensible species’ with ‘phantasm’ when the only evidence provided is that the term similitudo occurs in definitions of each. Once a sense faculty has been disposed properly with a sensible species, then it is capable of sensing. Sensation, however, is not explained sufficiently by only the passive reception of a form. Some contribution on the part of the perceiver is also required. This means that it is plausible to say that some person is in a certain state in which all the necessary conditions are present but that she herself is not perceiving the proper sensibles. This would be the case, for example, when she is staring blindly at a wall, and not conscious of sensing the colour of the wall. The requisite conditions would be present here: a red wall, sufficient light, and a properly disposed faculty. These alone, however, would not be sufficient for sensation. What is necessary is that the perceiver engage actively with the immuted sensible species and thus begin to have a sense awareness. Thus, in addition to the three necessary conditions for sensation—NC[O-M-F]—the perceiver also must contribute her part. It is only with this mental activity in conjunction with the necessary conditions that an act of sensation will take place at all. An adequate account of this activity depends on an analysis of the sensus communis, which is a faculty of the internal senses. The next chapter discusses how the sensus communis is an intricate and necessary faculty central to Aquinas’s account of sensation. In this end, it is the person who senses and perceives, but it is by means of the sense organs and faculties, both external and internal senses, that the acts of awareness are possible. This is how Aquinas offers his naturalistic explanation of sense knowledge. As this chapter concludes, it is more evident that Aquinas is an objective relativist in his theory of sensation. This claim of objective relativism depends upon the three-term necessary triadic relation as a necessary condition for sensation. This analysis is also in agreement with the claims of Stump and Jenkins of reliabilism in Aquinas. When any term of the triadic relation is not accounted for, so too will success in the awareness of proper sensibles be found wanting.
This brings to a close the analysis of Aquinas’s theory of sensation and sense knowledge in the scheme of a three-term necessary relation. It is a realist theory rooted in his intentionality theory, which demands the strict identity or isomorphism of structure or form between the knower and the thing known. This comes about from the naturalist position Aquinas adopts regarding the philosophy of mind, which in turn is at loggerheads with the foundationalist philosophy of mind and its accompanying internalism so common to modern philosophy, and with the resurgence of mentalism in recent cognitive theory.
This chapter is followed by a lengthy appendix divided in two parts: one from the Commentary and the second from the Supplementum for the Summa Theologiae. This set of texts offers a tidy summary of Aquinas’s analysis of sensation; furthermore, these texts, in particular those from the Commentary, are the best and most lucid expositions of a thesis of intentionality found in Aquinas’s many writings. A second Appendix discusses externalism and foundationalism.
-  Some commentators on Aquinas, both scholastic and analytic, have alluded to this position. Deelynotes that Suarez’s position on sensation was structurally similar to Locke’s—i.e. an image is required forsensation. Cf. John N. Deely: New Beginnings: Early Modern Philosophy and Postmodern Thought (Toronto:University of Toronto Press, 1994), 135. James B. South questions this role for an image in Suarez’s philosophy of mind: ‘Suarez and the Problem of External Sensation, Medieval Philosophy and Theology 10(2)(2001), 217-40.
-  More analysis of this set of issues will appear in the final sections of this book, where in addition theintelligible species used in concept formation and exercise will be discussed as another use of similitudo inAquinas.
-  In his After Aquinas: Versions of Thomism (Oxford: Blackwell, 2002), Kerr develops these themes atsome length. Cf. ch. 2, ‘Overcoming Epistemology’.