Abstract
Susanna Schellenberg’s The Unity of Perception brings together different strands within the philosophy of perception, integrating concerns from philosophy of mind, epistemology, and cognitive science under a single explanatory framework. This is both a central motivation of the book and a significant point in its favor, guaranteeing its interest to most anyone working on perception. The fundamental unifying factor that is meant to account for the disparate concerns is her account of perceptual capacities.
The book has four sections: Foundations (Introduction and Chapters 1 and 2), Content (Chapters 3–5), Consciousness (Chapter 6), and Evidence (Chapters 7–10). The first section is most significant, as there Schellenberg lays out her integrative approach to perception and develops with great clarity and detail a novel account, which she aptly terms capacitism. This section is also helpful in directing the selective reader to those chapters that would best fit their specific interests.
According to capacitism, an analysis of perception, which will serve simultaneously to explain the various roles it is taken to play—among other things, justifying empirical beliefs, grounding singular reference, accounting for the phenomenology of perception and perception’s distinct representational content—is to be carried out in terms of the employment of perceptual capacities to discriminate and single out particulars in our environment, for example, the capacity to discriminate and single out instances of red from instances of blue.
As the fundamental notion in Schellenberg’s project, such perceptual capacities require much more detailed discussion than is afforded here. Yet, their two most crucial characteristics are (a) that they are capacities whose function is to discriminate and single out particulars, and (b) that they are repeatable and general. Appeal to these features allows Schellenberg to accommodate two central, and seemingly competing, claims regarding perception that frame the entirety of the book. The first is the particularity of perception—the claim that perception is constituted by the particulars to which the perceiver is related. Particularity is motivated by a recognition that perceptual experiences (whether veridical or not) seem to provide us with empirical knowledge of particulars, and that when all goes well perception does provide us with such knowledge. The second claim concerns the general character of perception, which is largely motivated by the thought that veridical perceptions of qualitatively indistinguishable particulars (say, two white cups) as well as illusions and hallucinations (say, as of a white cup) may be phenomenally indistinguishable, thus suggesting that they share a common, general, constitutive element.
The seeming conflict should be plain. Particularity suggests, as against generality, that experiences of different particulars, even if phenomenally indistinguishable, are themselves distinct, as they are constituted by different particulars. In contrast, generality suggests that perception cannot be constituted by worldly particulars, as the numerical identity of the particular perceived or, indeed, even there being any such particular (as in the case of hallucination) need make no difference to the experience.
Nonetheless, capacitism overcomes this tension. According to Schellenberg, the first claim is secured because a perceptual state is partially constituted by perceptual capacities whose function is to single out the particulars to which one is perceptually related. And, when this function is satisfied, the resultant perceptual state is thereby partially constituted by the particulars singled out. The second claim is secured because the employment of a perceptual capacity constitutes the general contents and the phenomenal character of experience.
Taking these two characteristics together, we find that two perceptual states of different, yet qualitatively indistinguishable, particulars will be different states, as each is partially constituted by a different particular. Nonetheless, given that the particulars are qualitatively indistinguishable, successfully discriminating and singling them out employs the very same perceptual capacities, and will thereby be phenomenally indistinguishable. Furthermore, in cases of illusion or hallucination it is the, admittedly unsuccessful, employment of the perceptual capacity that nonetheless constitutes the phenomenal character of the experience. Thus, capacitism is a common-factor view of perceptual experience.
Reflecting on these two characteristics of perception—its particularity and generality—and capacitism’s ability to satisfy both, figures prominently in shaping Schellenberg’s views in the other sections. It is the core of her argument for a Fregean Particularist account of content (in Section 2), for her account of consciousness as a mental activity (in Section 3)—namely, the activity of employing a perceptual capacity (an account she terms mental activism)—and to her important distinction between factive and phenomenal evidence (in Section 4).
For brevity, consider Schellenberg’s treatment of representational content. In the second section, Schellenberg argues for two desiderata that any account of perceptual content must meet—the particularity desideratum and the phenomenal sameness desideratum—in order to characterize and later dissolve the tension between two dominant extant views in the philosophy of perception—austere relationalism and austere representationalism. The former is largely motivated by the particularity of perception. It takes perception to consist in an acquaintance relation to worldly particulars and rejects the notion that perception has any representational contents. It thereby rejects common-factor views of experience in favor of some form of disjunctivism. In contrast, the latter view is motivated in large part by the generality (i.e., phenomenal sameness) of perception, and holds that perception consists in general contents that are to serve as a common factor between veridical perceptions and illusions or hallucinations.
The appeal to perceptual capacities is supposed to strike a balance between particularism and generalism. With respect to the latter, perceptual capacities are the common factor that accounts for an experience’s general contents—their employment constitutes the content-type of an experience. In this way, capacitism rejects disjunctivism. Yet, to accommodate particularism, Schellenberg argues that perceptual experiences have not only a content-type but a token-content. In the case of genuine veridical perception, the token content is singular content, which consists of the very particular successfully discriminated and singled out by the perceptual capacity employed. In the case of illusion or hallucination, the employment of a perceptual capacity does not satisfy its function and the token-content is therefore gappy. Thus, her account accommodates the thought that perception is constituted both by general elements—the employment of a perceptual capacity—and by the particulars one is related to in cases of successful perception.
There is certainly much more that needs to be said about this very rich text, but let me end with one remark concerning the general project of capacitism. Although I am enthusiastic about the appeal to perceptual capacities, one worry throughout the book is the extent to which capacitism is a genuine advance over some form of representationalism. One of Schellenberg’s stated motivations for the book is her contention that perceptual capacities are prior in order of analysis to representational contents. Yet, it seems that any plausible representationalism already presupposes a form of capacitism, in that perceptually representing X involves the actualization (or employment) of some capacity to represent Xs. So, the question is, why is the capacity to discriminate and single out particulars of a given kind prior to the capacity to represent particulars of a given kind? Schellenberg argues that a necessary condition on one’s perceiving X is that one discriminates and singles out X. Yet representationalists, myself included, may find this questionable. Indeed, it seems at least equally plausible that it is on the basis of perceiving X, by representing it, that one is then able to discriminate and single it out from its surrounds. Further, it seems that one can perceive X even without thereby discriminating and singling it out, for example, when perceiving a uniformly red wall filling one’s field of vision. Schellenberg addresses this kind of objection (p. 27), yet I find her response wanting. According to Schellenberg, when looking at a uniformly colored wall, one is employing perceptual capacities, specifically, capacities to discriminate and single out the different parts of the wall, for example, the part on one’s left from the part on one’s right. However, an appeal to such perceptual capacities is unhelpful. After all, the perceptual capacities in play are supposed to constitute the contents and phenomenal character of the experience, and such spatial perceptual capacities are inadequate to account for our experiencing the wall’s color. To explain our experiencing the wall as red we would have to appeal to the perceptual capacity to discriminate and single out instances of red, yet this is ruled out by the fact that the wall is uniformly red. There is simply no surrounding color from which the color of the wall can be discriminated. A more natural explanation of our experience of the wall appeals to our representing its color independently of employing a capacity to discriminate and single it out. Given that one of Schellenberg’s main motivations is to reject representationalism in favor of a specific version to capacitism, one that grounds representational contents and phenomenal character in capacities to discriminate and single out particulars, I believe that more needs to be said about the primacy of such perceptual capacities.
The Unity of Perception is an interesting and thought-provoking book. The central view—capacitism—and its broad implications for philosophy of perception, epistemology, philosophy of mind, and cognitive science make this book a valuable contribution to anyone working on perception, and I have no doubt that it will draw a great deal of well-deserved attention.
