Many thanks to John Schwenkler for running the Brains blog and for inviting me to guest blog this week about my new book The Unity of Perception: Content, Consciousness, Evidence (Oxford: Oxford University Press, 2018).
Perception is our key to the world. It plays at least three different roles in our lives. It justifies beliefs and provides us with knowledge of our environment. It brings about conscious mental states. It converts informational input, such as light and sound waves, into representations of invariant features in our environment. Corresponding to these three roles, there are at least three fundamental questions that have motivated the study of perception:
Epistemology question: How does perception justify beliefs and yield knowledge of our environment?
Mind question: How does perception bring about conscious mental states?
Information question: How does a perceptual system accomplish the feat of converting varying informational input into mental representations of invariant features in our environment?
To be sure, many other questions have motivated the study of perception. To list just a few: What is the nature of the perceptual relation? What is the object of perception? How does perception guide action? What is the relation between perception and thought? But the way these questions are answered hinges on what stance is taken on the three fundamental questions.
The last decade has seen an explosion of work on the mind and information questions in both philosophy of mind and cognitive science. While there has been fruitful interaction between work in philosophy of mind and cognitive science, little has been done to integrate this work with issues in epistemology. Theories motivated by addressing the mind and information questions have been developed largely independently of concerns about how perception furnishes knowledge of our environment and how it justifies our beliefs. Similarly, theories motivated by addressing the epistemology question have been developed largely independently of concerns about how perception brings about conscious mental states. To be sure, most accounts of perceptual justification rely heavily on the idea that perception justifies beliefs in virtue of its phenomenal character. However, such accounts typically take it as given that perception provides evidence and immediately proceed to addressing the question of what the relationship is between such evidence and relevant beliefs. This split between philosophy of mind and cognitive science on the one side and epistemology on the other has hindered our understanding of perception. Questions in philosophy of mind are intimately connected with questions in epistemology in particular with regard to perception: the role of perception in yielding conscious mental states is not independent of its role in justifying our beliefs and yielding knowledge. If this is right, then perceptual experience should be studied in an integrated manner.
My book develops a unified account of the phenomenological and epistemological role of perception that is informed by empirical research. So it develops an account of perception that provides an answer to the first two questions, while being sensitive to scientific accounts that address the third question. In developing such a unified account, this book aims to advance a rigorous way of doing philosophy of mind on which mental states are analyzed in light of scientific evidence while being sensitive to their epistemic, cognitive, and phenomenological role. It aims to be conceptually disciplined and empirically constrained. It is written so that it should be useful to both philosophers and scientists familiar with philosophical and scientific debates about perception; as well as those unfamiliar with these debates.
The key idea is that perception is constituted by employing perceptual capacities—for example the capacity to discriminate and single out instances of red from instances of blue. Perceptual content, consciousness, and evidence are each analyzed in terms of this basic property of perception. Employing perceptual capacities constitutes phenomenal character as well as perceptual content. The primacy of employing perceptual capacities in perception over their derivative employment in hallucination and illusion grounds the epistemic force of perceptual experience. In this way, the book provides a unified account of perceptual content, perceptual consciousness, and perceptual evidence. What unifies the account are perceptual capacities. Due to the grounding role of perceptual capacities, we can call the view developed in this book capacitism.
Such a unified account of perception opens up a new understanding of the nature of perceptual content, perceptual particularity, the phenomenological basis of evidence, the epistemic force of evidence, the origins of perceptual knowledge, the relationship between content and consciousness, as well as the relationship between consciousness and reference. Moreover, it clears the way for solving a host of open-standing problems, such as the relation between attention and perceptual knowledge, the linguistic analysis of perceptual reports, the relation between acquaintance and awareness, the rational role of perceptual experience, and the perceptual basis for demonstrative reference.
One larger aim of this book is to bring back mental capacities as a way of analyzing the mind. Despite their prominence in the history of philosophy, capacities have been neglected in recent philosophical work. By contrast, appeal to mental capacities is standard in cognitive psychology and the brain sciences. This book develops the notion of capacities in light of empirical work in cognitive psychology, neuroscience, and developmental psychology. While it is based in contemporary empirical sciences, it also harks back to a long tradition of analyzing the mind in terms of capacities. It turns out that we can use contemporary insights and tools to modernize that tradition.
Analyzing the mind in terms of capacities has many advantages, so it is surprising that recent philosophy has forsaken this approach. One central advantage is that it allows for a counterfactual analysis of mental states on three interrelated levels. On a first level, we focus on the function of mental capacities. On a second level, we focus on the mental capacities employed irrespective of the context in which they are employed. On this level, the focus is on what perception and corresponding cases of hallucination and illusion have in common. On a third level, we focus on the mental capacities employed, taking into account the context in which they are employed. On this level, the focus is on the difference between cases in which a capacity fulfills its function (perception) and cases in which it fails to fulfill its function (hallucination and illusion). I explain these terms in more detail in Chapter 2.
Let me locate capacitism within the wider philosophical landscape.
First, capacitism grounds mental states, consciousness, evidence, and content in the physical, non-mental world. As such, these features of the mind are no less amenable to scientific investigation than any other features of the world. In developing such a naturalist and physicalist view of perception, this book shows how perception is our key to the world while situating perception within that world.
Second, capacitism is an externalist account of perceptual content, consciousness, and evidence. It is an externalist account since the perceptual capacities that constitute these features of the mind function to discriminate and single out particulars in our environment. Due to their singling out function, perceptual capacities connect us to our environment. While capacitism is an externalist view, it is one that that does justice to the internalist elements of perceptual experience. In contrast to, say, orthodox versions of reliabilism, it makes room for conscious mental states that play a cognitive and epistemic role in our lives. Moreover, the capacities employed in perception can be employed derivatively in hallucination and illusion. While they do not fulfill their function when employed in hallucination and illusion, the capacities nonetheless function to discriminate and single out particulars, thereby providing a relation to how things would be were they to fulfill their function. By doing justice to the internalist elements of perceptual experience, capacitism is a modestly externalist view.
Third, capacitism is a common factor view of perception. The same perceptual capacities can be employed in perception, hallucination, and illusion. As such, they can constitute a metaphysically substantial common element. This common element grounds not only the common representational content of perceptions, hallucinations, and illusions with the same phenomenal character (Chapter 4 and Chapter 5), but also perceptual consciousness (Chapter 6) and phenomenal evidence (Chapter 7 and Chapter 8). Thus, capacitism is at its core non-disjunctivist.
Fourth, capacitism is an asymmetric account of perception, hallucination, and illusion. While, it is a non-disjunctivist account, it nonetheless holds that perception is metaphysically and explanatorily more basic than hallucination and illusion. Perception is more basic since perceptual capacities function to do what they do in perception, namely discriminate and single out particulars, and they have this function, even when employed in hallucination or illusion. So while they can be employed in hallucination and illusion, they are employed derivatively.
So capacitism walks a path between two traditional views: the common factor view and austere relationalism. The common factor view posits that a perception, hallucination, and illusion with the same phenomenal character share a common element that grounds their shared phenomenal character. Typically, the additional condition that makes for successful perception is considered to be a causal relation between the experiencing subject and the perceived object. (This approach is analogous to the epistemological view that knowledge can be factorized into belief and some additional element, say, justification.) By contrast, austere relationalism characterizes hallucination in terms of a deficiency of perception and argues that perception and hallucination do not share a common element. (This approach is analogous to the view that mere belief is to be analyzed as deficient of knowledge, but subjectively indiscriminable from it.)
With common factor views, I argue that perceptions, hallucinations, and illusions with the same phenomenal character share a metaphysically substantial common factor that grounds their phenomenal character. The common element is constituted by the perceptual capacities employed. But with austere relationalists, I argue that hallucinations and illusions can be understood only in terms of a deficiency of perceptions: there is an asymmetric dependence of the employment of perceptual capacities in hallucination and illusion on their employment in perception. I show how this way of understanding the metaphysical structure of perceptual experience can be exploited for a view of perceptual evidence.
The book has four parts. Each part develops a component of my positive account. In the rest of this week, I will devote each day to one of the four parts.
 No doubt, dependencies run in the other direction as well: what stance one takes on, say, the question of what the object of perception is, will affect one’s answer to the three fundamental questions. But arguably there is an asymmetry in the order of explanation between the three fundamental questions and the other questions.
Header image: Gerhard Richter, Abstraktes Bild, See