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Home arrow Economics arrow Aquinas’s theory of perception: an analytic reconstruction



Phantasm-2 is involved in the process by which the perceiver, utilizing the vis cogita- tiva, is aware of an external object as an individual object of a certain natural kind. In the Commentary on the Soul, Aquinas wrote: ‘If an apprehension is of some individual object, as when a perceiver sees this particular coloured thing, he perceives this particular man or beast, then the vis cogitativa is at work’ (no. 396).

With the vis cogitativa, an object is not perceived merely as a bundle of sensations. The vis cogitativa is a mental faculty of inner sense. This inner sense faculty so conditions an act of direct awareness that an individual object in the external world is not perceived only as a bundle of sensible qualities, which is the result of sensation by means of the external sensorium alone. Through the vis cogitativa, the individual is perceived as a unitary, substantial individual object or thing.[1] It is by means of the structured awareness of the vis cogitativa that Aquinas differs radically in matters of sense perception from the classical British empiricists. That the object of direct perception for the early British empiricists is a bundle of sensations, i.e. a collection of primary and secondary qualities, is obvious from even a cursory reading of Berkeley and Hume. The vis cogitativa, by means of Phantasm-2, so structures an act of direct awareness that the object in the external world, the concretum, is interpreted perceptually as a specific, unified whole of a particular kind, and not merely as a collection of proper and common sensibles. The vis cogitativa contributes an additional aspect to direct perception above and beyond that accounted for by means of the external senso- rium alone. In order to explicate further this suggestion, it is important to recall the following important passage from the Summa Theologiae:

Sense powers know things by being impressed with their likeness [similitudo]. However, this likeness can be understood in three different stages.

First, immediately and directly; this is when the likeness of colour is in the faculty of sight. This is true of all the other proper sensibles in their appropriate sense faculties.

Secondly, directly, but not immediately, as when the likeness of shape or size is in the sight. This is true of all the other common sensibles shared through several different senses.

Thirdly, neither immediately nor directly, as when the likeness of a man is in the faculty of sight. He is there [i.e. in the faculty of sight] not because he is a ‘man’ but rather because he is a coloured object. (Summa Theologiae, I q. 17 a. 2; emphasis and bold added)

This passage is interesting, informative and challenging philosophically. It speaks to the differences in the use of similitudo considered at the end of the preceding chapter. The similitudo, which Aquinas considers when treating of both the proper and the common sensibles, is Likeness-1. Both of these are caused directly by the sensible qualities existing as causal factors in the external world. However, Aquinas considers the incidental object of sense, which in the above passage is also spoken of as a likeness; this object is not being caused by the object as directly perceived or perceivable. In other words, the similitudo of ‘this man, what both Aristotle and Aquinas call the ‘incidental object of sense, is not directly and exhaustively a result of the causal factors of the sensible qualities existing in the external world. Some translations render this sensible object as a per accidens object of sense. Note how Aquinas refers to the objects of direct perception in the above passage: ‘as when the likeness of a man is in the faculty of sight. He is there [. . .] not because he is a “man” but rather because he is a coloured object.’ In other words, the external senses in conjunction with the sensus communis do not perceive ‘man’ as such. Rather they perceive a collection of sensible qualities. This is the product of a conjunction of a series of necessary triadic relations.

In Aquinas’s theory of sensation, the external sensorium has for its object—the conjunction of the series of necessary triadic relations—the same type of collection as Berkeley speaks of in the Principles and Hume in the Enquiry. However, it is important to note that none of the terms of this series of necessary relations is identified with the

similitudo of ‘man, which is the incidental object of sense. In some way, therefore, in order to account for the possibility that a human perceiver has an awareness of individuals of a kind and not merely as a bundle of sensations, a contribution or interpretive dimension by means of the internal sensorium is a necessary condition. This act of awareness is explicable only if the vis cogitativa itself contributes an interpretive element to the act of direct awareness. The result is that a bundle of sensations can be perceived as an individual and not merely as a collection of sense qualities. The vis cogitativa, therefore, is an active contributor to direct awareness. This active contribution is explained structurally by Phantasm-2. Therefore, Phantasm-2 is the vehicle of inner sense, which provides a ‘conditioned awareness’ of bundles of sensations in order that these bundles might be perceived as individuals of a kind. It is with this inner sense—the vis cogitativa—that Aquinas goes beyond the analysis of perception proposed by Berkeley, Hume, and most empiricists in modern and contemporary philosophy.

In offering this analysis of perception, Aquinas is aligned structurally with Thomas Reid. Like Reid, Aquinas, to be sure, is not a Humean by any stretch of the imagination. Aquinas’s account has a philosophical affinity with Reid; neither is an empiricist or a closet Kantian. The suggestion put forward here is that Aquinas accepts the distinction between sensation and perception. In addition, he would argue that a category difference exists between these two types of sense knowledge. To help explicate how this occurs in the texts of Aquinas is the goal of much of what remains in this chapter. The importance of the present discussion is the link made between the act of awareness proper to the vis cogitativa and the role of Phantasm-2 in this mental act of the vis cogitativa.

It must be emphasized that, given the structure of Aquinas’s epistemology, the conditioned awareness of the vis cogitativa is not a direct datum of experience provided by the external sensorium. An individual as an individual, which is the ‘incidental object of sense, is incapable of being a causally efficacious object. In the following passage from the Commentary on the Soul, Aquinas indicates explicitly this non-causal relation, which is characteristic of the incidental object of sense:

We might [. . .] call Diarus or Socrates incidentally a sense object because each happens to be white: What is sensed incidentally happens to belong to what is sensed absolutely [per se]. It is incidental to the white thing, which is sensed absolutely, that it should be Diarus; thus, Diarus is a sense object incidentally. He does not as such act upon the sense faculties at all. (Commentary on the Soul, no. 387; emphasis added)

In the external world, the individual as an individual is not reducible to one of the terms of the triadic relation necessary for the exercise of the external senses. Another text indicates the non-causal efficacy of the incidental object of sense: ‘But whatever makes no difference to the immediate modification of the sense faculty we call an incidental object of sense. Therefore, Aristotle says explicitly that the senses are not affected at all by the incidental object of sense as such (no. 393; emphasis added).

This sense of similitude associated with the vis cogitativa must be a different intentional category from the use of similitude found with the proper and common sensibles, which is Likeness-1. This likeness associated with the incidental object of sense is an example of Likeness-2. Yet it cannot be coextensive with Phantasm-1. Phantasm-1 has no more content than that given by the external sensorium. The incidental object of sense is by its very nature, however, something more than the data sensed through the external sensorium. Accordingly, the incidental object of sense must have a phantasm, which is distinct from Phantasm-1. This different phantasm is what this analysis proposes calling Phantasm-2. In other words, it is by means of Phantasm-2 that a perceiver is able to recognize Megan as Megan the person and not just as a specific bundle of proper and common sensibles. Nonetheless, Phantasm-2 is not an object of direct awareness. Phantasm-2 does not function as an idolum or species expressa. If this were to occur, then Phantasm-2 would be a tertium quid, and Aquinas’s position would devolve into representationalism. The act of awareness of the vis cogitativa, therefore, is not of a phantasm as an object. On the contrary, Phantasm-2 structures the very act of awareness of the vis cogitativa so that a bundle of proper and common sensibles can be perceived as an individual. In other words, Phantasm-2 is a ‘conditioning’ or ‘structuring’ of the mental act of the vis cogitativa. This ‘conditioning’ enables the perceiver to interpret an individually sensed bundle of sensible qualities as this particular object of this natural kind. Accordingly, the incidental object of sense is an object of the conditioned awareness of the vis cogitativa. If this conditioning accomplished by means of Phantasm-2 is omitted, then so too is the incidental object of sense as an object of knowledge. Phantasm-2 and the incidental object of sense are not equivalent. Rather, Phantasm-2 is a necessary condition for the awareness of the incidental object of sense through the vis cogitativa. Phantasm-2 is a process structure through which human perceivers are aware of individual primary substances.

The incidental object of sense corresponds to the particular thing in the external world which both Aristotle and Aquinas call a ‘primary substance’. In the Commentary on the Metaphysics, Aquinas writes explicitly that ‘videtur esse substantia et hoc aliq- uid’ (bk XII, lect. 3). This primary substance, however, cannot be perceived by means of the external sensorium alone. As the classical British empiricists taught generations of Western philosophers, the external sensorium obtains only a grasp of the collection of sensible qualities. The textual evidence provided above should substantiate this claim. It is by means of Phantasm-2, however, conditioning or structuring the act of the vis cogitativa, that the incidental object of sense can become an object of knowledge. The epistemological import of Phantasm-2 is in enabling an act of awareness to interpret a particular bundle of sensations in a certain way. Thus, Phantasm-2 is not an object at all. Rather, it is what constitutes the structured awareness of a set of proper and common sensibles. This ‘conditioning’ of an act of awareness via Phantasm-2 is an instance of a ‘structured mental act’. Parenthetically, both Wisdom and Chisholm share this concern about perceiving ‘things’ rather than merely ‘collections of sensible qualities’.7

There is a connection between Phantasm-1 and Phantasm-2. Phantasm-1 is a necessary condition for Phantasm-2. Phantasm-2 cannot occur unless previous sense experiences through the external sensorium have taken place, which produced Phantasms-1. One might look at the vis cogitativa as utilizing the residue stored in the thesaurus of the vis imaginativa in producing its own structured awareness via Phantasm-2. In other words, Phantasm-2 cannot occur in a vacuum. This is analogous to Kant’s claim that reason without sense is blind.8 The structured awareness of the vis cogitativa via Phantasms-2 builds upon the content of Phantasm-1. However, Phantasm-1 does not exhaust the content of Phantasm-2. The vis cogitativa utilizes Phantasms-1 in producing its structured awareness of the data presented to it by the external sensorium. Accordingly, Phantasms-1 are necessary but not sufficient conditions for the production of the structured awareness contributed by Phantasm-2. It must be emphasized that Phantasm-1 is not a sufficient condition for Phantasm-2. This merely reiterates the claim that the internal sensorium is itself an active contributor and is not just a passive receptor of sensations or impressions.9 The internal sensorium, because of the vis cogitativa, is an active process structurally interpreting the collections of sensations, which have been unified in the external sensorium. In the case of the conditioned awareness of the vis cogitativa, this internal sense actively interprets a certain set of data—which is the collection of proper and common sensibles—as a particular thing of a specific kind.

The foil for this elucidation of Aquinas on inner sense is the set of texts rooted in classical British empiricism, with special reference to Berkeley and Hume; this became known as the ‘bundle view’ of perception, and was articulated with philosophical vehemence. While Reid offered a critique of this position, he nevertheless failed to offer an analysis other than by wishful thinking concerning how his position transcends what Berkeley and Hume proposed. Aquinas’s account of the vis cogitativa, on the other hand, provides a structural account of how the perception of the individual as opposed to merely an awareness of a bundle of sensations is possible. This analysis, therefore, is an elucidation—an explicatio textus—of the claim that a necessary condition for perception in Aquinas’s philosophy of mind is the working of the vis cogitativa.10 [2] [3] [4] [5]

  • [1] This individual object is what Leibniz called a .
  • [2] This is not to suggest that Wisdom, Chisholm, and Aquinas provide identical or even similar explanatoryaccounts of perception. It does suggest, however, that these philosophers were concerned over the possibility ofperceiving things as unitary, substantival objects and not merely as bundles of sensations. See RoderickChisholm, ‘On the Observability of the Self, Philosophy and Phenomenological Research (1969), 7-21.
  • [3] Immanuel Kant, Critique of Pure Reason, trans. Norman Kemp Smith (London: Macmillan, 1929,A103ff.; B147ff.
  • [4] Hume claimed that the distinction between impressions from the external sense and ideas of theinner sense was that the latter were nothing more than faint copies of the former. The essential passivityof sensation is paramount in the psychological atomism of Hume. Such passivity is foreign to Aquinas’snotion of inner sense.
  • [5] In his Four Ages of Understanding (Toronto: University of Toronto Press, 2001), John N. Deelyconsiders this neglected set of issues in classical Thomism and introduces the work of John Poinsot(John of St Thomas) as offering a response to this aporia in Aquinas’s texts.
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