Home Economics Aquinas’s theory of perception: an analytic reconstruction
Reid, Gibson, and Aquinas: Epistemological Naturalism Revisited
Chisholm and Haldane have suggested that Aquinas’s philosophy of mind is similar to what one finds in the writings of Thomas Reid. Haldane comments on this similarity: ‘Like Thomas Reid writing five hundred years later, Aquinas himself is simply trying to identify at the level of metaphysical description what is implicit in our everyday dealings with the world.’ Nonetheless, it seems that Aquinas shares some metaphysical convictions with Moore and Reid. In fact, Haldane writes that ‘[t]he similarities between Reid’s “new found” realism and long established scholastic orthodoxy are striking. He further writes that Reid’s ‘theory bears a remarkable resemblance to that of St. Thomas and later scholastics: and from the language, structure and content of
Reid’s arguments it is impossible to resist the conclusion that [...] he was influenced by the philosophy of the schools.’
Reid, Kneale once wrote, rescued the word ‘perception’ from the early modern philosophers where (Kneale suggests) the term ceased to have any clear meaning.  Empiricists like Hume thought themselves entitled to use ‘perception’ as an ‘omnibus word’ for whatever goes on in the mind. On matters of perception, Aquinas differs radically from Hume. Aquinas’s analysis is reminiscent of Strawson’s ‘descriptive metaphysics’, and is a philosophical defence of common sense.11 Moreover, Aquinas would neither deny nor belittle the importance of what contemporary cognitive scientists call ‘folk psychology’.
The explicatio textus of sense organ and sense faculty in the Commentary is remarkably similar to the method articulated by Gibson in discussing the evolutionary development of human sense organs. It is through this evolutionary development, Gibson maintains, that a human knower can make his or her way around the environment. This position is often referred to as ‘ecological perception theory’. One needs to broach the subject of naturalism inherent in Aquinas’s philosophy of mind. The explicatio tex- tus suggested here is remarkably similar, it would seem, to the method articulated by Gibson in discussing the evolutionary development of human sense organs. It is through this evolutionary development that a human knower can make her way around the environment. In the Commentary on the Metaphysics, when discussing the three levels of knowledge found in animals other than human persons, Aquinas writes about the need for memory in higher animals.
For since sensory cognition enables animals to make provision for the necessities of life and to perform their characteristic operations, then those animals that move towards something at a distance by means of local motion, must have memory. For if the anticipated goal by which they are induced to move did not remain in them through memory, they could not continue to move towards the intended goal that they pursue. (Commentary on the Metaphysics, bk 1, no. 10)
In this passage, one notes that because of the need that an animal has to move towards some necessary item in the world, the animal has developed for the purpose of survival some ability for memory. Aquinas includes humans in the animal realm. Accordingly, he provides a naturalist account of this development in the animal, which appears to be moving towards Gibson’s analysis.
In De Veritate, Aquinas is more explicit in explicating his general method in determining how the sensitive powers of the animal arise. The following passage exhibits a strong evolutionary drive:
But, if we study the matter carefully, we find that in both types of powers, acts and objects are not only signs of diversity, but in some way causes of it. For every thing which has existence only because of some end has its manner determined for it from the end to which it is ordained. Thus, a saw has this kind of form and this kind of matter in order to be suitable for its end, which is to cut. But every power of the soul, whether active or passive, is ordained to act as to its end, as is clear in the Metaphysics. Hence, every power has a definite manner and species by reason of which it can be suitable for such an act. Therefore, powers are diversified because the diversity of acts requires different principles from which to elicit acts. Moreover, since object is related to act as its term, and acts are specified by their terms, as is plain in the Physics, acts must also be distinguished according to their objects. Therefore diversity of objects brings about diversity of powers. (De Veritate, q. 15 a. 2; emphasis added)
Aquinas argues explicitly that the sensitive faculties or powers are what they are because of the objects in the external world. Were these objects not in rerum natura, the sensitive powers would not have come about. This is another indication of the naturalist elements influencing the structure and development of Aquinas’s philosophy of mind.
While Gibson does not affirm an ontology of holistic primary substances, he does consider the role the environment plays in determining how sense organs and faculties have developed and function. The same is true, mutatis mutandis, for Aquinas. This gives certain value to Aquinas’s oft-repeated claim that ‘nature does not act in vain’ and that ‘the knowing faculty is made for the act of knowing, which in turn is made for the object of knowing’. ‘The first things known are things outside the mind to which the intellect is first directed in thought’ (De Potentia, q. 7 a. 9).
In discussing direct realism in medieval philosophy, Kemp suggests several significant connections with Gibson’s account: ‘Another issue in modern psychology that parallels one raised in medieval perception concerns the extent to which perception is direct. [. . .] An alternative modern approach, again suggested by Gibson, is that perception is direct and does not require mediating processes [. . .].’ In this account of Gibson, while considering the lack of mediating principles in perception, Kemp suggests that Gibson’s position ‘does not require knowledge of the object. Hence, while direct, it depends on a variety of stimulus cues that are found in the external world. Aquinas, to be sure, requires the existence of a world of primary substances, which are individual hoc aliquids; while Gibson and Aquinas have several interesting structural similarities in discussing perception, their two theories of perception are neither identical nor isomorphic.
Following interpretive insights from Gibson’s analysis, this set of teleological expressions found in Aquinas’s texts might be his way of introducing a version of
‘epistemological naturalism’. Haldane notes that contemporary philosophers can learn a significant meta-philosophical method from Aquinas: ‘[If philosophers . . .] follow Aquinas and Quine and distinguish philosophical explanation from justification, then there is no general problem of inductive scepticism that the philosopher or anyone else is obliged to answer.’ Haldane suggests that in much contemporary philosophy of mind, there is ‘a conflict between two fundamentally opposed positions: Cartesian representationalism and naturalistic, cognitive psychology [. . . and] Aquinas’s theory is located within the naturalistic tradition [. . .].’ Aquinas’s naturalism argues that perception and thought are human activities involving cognitive responses to influences of the external environment. This connection with the external environment a fortiori suggests the rejection of a Cartesian position, which accounts for the mind as an autonomous self-contained and environment-independent self—a res cogitans.
One must understand what this position on Aquinas and naturalism means. There are at least three senses of naturalism in philosophy-of-mind discussions regarding Aquinas:
Aquinas, through the use of his theory of intentionality, accepts the second position of naturalism but rejects the first. This is the equivalent of Aquinas’s claim that ‘nature does not act in vain’. In agreement with Haldane’s suggestions, intentional capacities or dispositions may be ‘a very special case of the teleological’. In addition, the first position would apparently reject Aquinas’s distinction between immanent and transient action. The rejection of the third position is of an interpretation adopted by Pasnau and by Smit. The argument against interpreting Aquinas in a manner reducible to divine illumination will be discussed later in this book.
In the end, Aquinas argues that the structure of the sense organs and faculties are best suited to be aware of the world as it is. In his Quaestiones Disputatae de Anima, Aquinas writes: ‘If anyone wants to examine also the particular organs of the human body, she will discover that they are organized so that a human being might engage in sense knowledge most effectively. [. . .] One can determine the meaning of the human body with respect to the particular features that belong to a human being by nature’
(q. 8). Aquinas appears to suggest that a human being is what it is by nature in order for that individual human person to get along better in his encounters with the external world. While Aquinas was certainly not opting for a theory of natural selection, his conclusions are strikingly similar. Kenny once wrote: ‘Aquinas is surely correct to insist that the way to understand the nature of a sense is to start by looking at the objects which fall under it.’ Kerr writes that Aquinas ‘has a proto-Wittgensteinian conception of how subjective experience depends on our engagement with objects in the public world’.
Pasnau provides an informative account of teleology in Aquinas on sensation, which he develops in terms of a functional analysis: ‘Most of Aquinas’s functional analysis could stand without any such theological assumptions. [. . .] To continue to speak of function and purpose in the absence of design would require some account of how these terms are being used, but there is no reason to suppose such an account unavailable.’ Pasnau’s point is compatible with the suggestions from Gibson’s ecological perspective on psychology. It is towards inhabiting this arena that the analysis in this book is directed. Stump, however, would question this point. She argues that the sense organs and faculties are ordered to specific objects of awareness only because God set us up that way. This is a particularly vexing issue in Aquinas’s ontology, to which the discussion in this book is but a sketchy response. In his Warrant and Proper Function, Plantinga argues that a naturalistic account of the evolutionary development of cognitive faculties is not sufficient to guarantee the reliability of these faculties. He accordingly argues that reliability entails a supernatural or divinely based ontological theory. In ‘Cognitive Faculties and Evolutionary Naturalism’, Cantens argues against the irrationality of naturalism maintained by Plantinga. In addition, in asking the reliability question about naturalistically based cognitive developmental theories, Plantinga appears to adopt a Cartesian methodology, seeking justification and not explanation. While these arguments cannot be discussed in the detail required here, nonetheless Cantens has argued plausibly that the Plantinga thesis need not be accepted without a serious rejoinder.
Cantens, Gibson, and Pasnau would respond that the realist connection of objects to faculty is reducible to the process of human evolutionary developments. Pasnau notes the following:
It is easy to see how one could mount an evolutionary defence of the principle that ‘nature does not fail in necessary things’. Animals that fail at necessary details will not (very often) reproduce. Deficient genes will not be passed on, and deficient animals will tend to be rare. ‘Except for a few cases’, then, animals will have all of the capacities they need to have.
This explicatio textus of sense organ and sense faculty in the Commentary again appears remarkably similar to the method articulated by Gibson in discussing the evolutionary development of human sense organs. It is through this evolutionary development, Gibson suggests, that a human knower can make his way around the environment. This teleology is a signpost suggesting Aquinas’s way of bringing a version of ‘epistemological naturalism’ into the discussion. Aquinas might respond also that the form of the evolutionary process is determined by Augustine’s rationes seminales, which are reducible to the divine plan working itself out in the course of time. Stump also argues that Aquinas holds that the human possibility for error is a result of original sin, and suggests that the evolutionary thesis is not finally reconcilable with Aquinas’s theological concerns. Nonetheless, it is possible to account in naturalistic terms for the function of the sense powers as directed to the respective objects. This is an explanatory and not a justificatory account. The divine appeal seems reducible to a justificatory criterion, which is beyond the issues posed by Aristotle and Aquinas. This direction notes the naturalism that is congruent with the philosophy of mind as articulated by Aquinas. Like Gibson, Aquinas would agree that the ecological development of the faculties of the external senses have been determined by the structure of the obj ects of sensation.
This issue of naturalism is controversial, to be sure. Aquinas at minimum offers an explanatory account of perception in terms of faculties and acts being determined by their objects. However, while he would not, it appears, adopt a ‘survival of the fittest’ method ofjustification, the passages from the Commentary on the Metaphysics and the De Veritate point in this adaptive direction. In other words, in discussing naturalism, two propositions must be articulated with care:
Aquinas adopts in some form both these propositions. Because the objects of knowledge are what they are, the knowing faculties have been developed—or created by God when human nature was first formulated in the divine mind. Secondly, it is with the knowing faculties that one is better able to navigate the world with other primary substances. The passage from the Commentary on the Metaphysics indicates enabling ‘animals to make provision for the necessities of life’, and thus these animals ‘must have memory’. Accordingly, no memory entails no survival. Of course, this is all in accord with Divine Providence, which, like Augustine’s rationales seminales, works out human development over time. Nonetheless, in his explanation of cognitive activities, Aquinas appears to have adopted a modified form of naturalism. This position is in accord with Haldane’s claim that both Aquinas and Quine are philosophical naturalists when considering cognitive activities.
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