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Perception and the Cartesian Theater


V.J. Torley has written a thoughtful reply to my recent post about perception. I appreciate his insights, which are substantial, but I disagree with his basic premise. I wish to assure him here that I am not, as the graphic accompanying his post would suggest, barking at the moon.


[Egnor] makes a fantastic claim which is foreign to Aristotle’s thinking: he asserts that whenever you perceive a distant object, your perception of that object occurs outside your body, rather than inside it.

Torley quotes Aristotle from several passages in De Anima, argues against my view, and concludes:

…my perceptions are located partly in my sensory organs, and partly in my brain. Insofar as they are perceptions of external objects, my perceptions can be located in the organs affected by those objects. But insofar as they are conscious, my perceptions are located in my brain — and in particular, my neocortex, and especially the association regions, which play a central role in consciousness…. I’m about as certain as I can be of anything, that when i look at the moon, my perception of the moon is somewhere within my body, and not on the moon.

The general question at issue is this: What is perception? Specifically, where (if anywhere) does perception take place? And another question: what did Aristotle have to say about it?

Before I proceed, some background will help. The traditional Aristotelian view of perception is that the objects of our perceptions are things in the real world. When we perceive a tree, we perceive the tree itself.

With the rise of early modern mechanical philosophy, the mechanists challenged this venerable view of perception. The challenge had its genesis in Descartes and Hobbes, but the most rigorous articulation of this new view was that of Locke, in his Essay Concerning Human Understanding. Locke asked: When I am conscious, what am I conscious of? He answered that he was conscious of ideas, which he defined as wholly subjective mental entities. Locke offered his Causal Theory of Perception: The world causes our ideas/perceptions, and what we are directly aware of is only our own ideas, not the world itself.

This general view that we observe our own internal ideas, and only our own internal ideas, has its genesis in Cartesian dualism, which posits a res extensa, which consists of material objects extended in space, and a res cognitans, which consists of an immaterial mind — a separate substance — which knows objects in the res extensa only via incident primary qualities (objective quantifiable properties). Secondary qualities (subjective qualitative properties) are the creation of our minds, in this view, not actually inherent in the external world.

This sort of view — that the immediate object of our perception is an idea in our mind, rather than an object in the world — has become the cornerstone of our modern view of the mind and is the (largely unexamined) predicate for modern neuroscience. It afflicts materialist neuroscientists and philosophers pervasively, and it even afflicts scientists and philosophers who work from a (more insightful) Aristotelian perspective. Of course the materialists eliminate the res cognitans entirely, and then struggle with the absurdities that emerge, but the Cartesian dualistic framework remains, minus one of its two pillars.

Daniel Dennett has coined a term that I think describes this misconception quite nicely (although I share few of Dennett’s views otherwise). He calls it the Cartesian theater. The Cartesian theater is what remains of Cartesian dualism after the immaterial mind is removed. Dennett envisions it as a tiny theater in your brain in which your observing self — your little homunculus — sits watching the show that your brain provides of your sensations, perceptions, images, memories, intellection, etc., presented on stage for you to experience. It is nice metaphor for the Lockean Causal Theory of Perception — for the theory that what you actually perceive is the perception in your brain, not the object of your perception in the real world. This is a profound mistake.

Now back to V.J. Torley’s post. Torley, who works from an Aristotelian perspective, agrees with the view that when we perceive, we perceive objects in the real world. But he takes issue with my assertion that the location of the perception is at the object perceived, rather than at the sense organ or in the brain. He suggests that perception takes place at the sense organ and in the brain, but does not take place external to the body at the object perceived. And he believes that Aristotle sides with him, not me.

Aristotle takes up perception in De Anima II 5 and 12. In Chapter 5 he explores perception in detail, and in Chapter 12 he explores perception from a hylomorphic perspective. Aristotle’s perspective is highly physiological — he is the original biologist, after all — although his hylomorphic perspective entails a rather different understanding of the metaphysical framework of biology than we generally have today.

Aristotle posits that perceptions entail proper external objects, organs (eyes, ears, mouth, etc.) and a medium such as air or food. The perception then is known via a thinking organ.

The process by which Aristotle believes perceptions are known is, however, quite unlike the Cartesian/Lockean physiology to which we moderns hew.

Aristotle writes (at the conclusion of DA II 5):

The perceiver is potentially what the perceptible object actually is already, as we have said. When it is being affected, then, it is unlike the object; but when it has been affected it has been made like the object and has acquired its quality.

This is, I believe, at the crux of Aristotle’s understanding of perception. The perceiver has the potency (potentiality) to become what the perceived object is. With the act of perception, the perceiver actually becomes, in a sense, like the object he perceives.

Of course a critic of my view that perception of the moon occurs at the moon will now need sedation: I have claimed that the perceiver of the moon actually becomes the moon. Keyboards will be ruined by spit coffee.

But it’s true, in a very specific way, and it is the essence of what Aristotle said. It is in the nature of forms that the acquisition of a form confers upon the acquiring thing the qualities of the form acquired. When wood becomes a chair, it acquires the qualities of a chair. The soul is a unique kind of form — it possesses other forms and yet remains itself. In this sense, the soul grasps the form of the object it perceives, and acquires the qualities of the object it perceives, without ceasing to be a soul. These grasped qualities are the extractable sensible qualities of the object of perception. The perceiver, in this sense, becomes like the thing perceived.

This is, I believe, what Aristotle meant when he wrote: “the soul is in a way all existing things…” (De Anima iii 8). This does not mean that the perceiver of the moon becomes like the moon essentially (fully) — a huge rocky spherical body. It means that the act of perception genuinely entails possession of the sensible principles of the object perceived — the qualities of the moon such as its shape, its color, its size, its location, etc. — by the soul, while the soul remains itself. We have the object of perception — at least the sensible principles of the object of perception — in our soul when we perceive. In the Aristotelian (Thomist/Scholastic) perspective, perception is a kind of possession — a kind of identity with the object perceived. We don’t merely see it. We possess it, in a specific way, in our soul, as a perception, or as a memory, or as an image.

Notice the radical difference between the Aristotelian view and the Cartesian/Lockean view. If we perceive the moon in the Cartesian theater, we merely perceive an image of it, metaphorically projected on a screen to be viewed by the homunculus in our brain. We never actually perceive the moon itself — we merely watch the matinee produced by our brain and organs of sense.

In the Aristotelian view, when we perceive the moon, we perceive the moon itself — we possess the moon, not just in a manner of speaking, but in a quite real way, as a sensible principle grasped by our soul. We perceive the actual moon, not merely a movie about the moon.

Now I suspect that this general Aristotelian view is acceptable to V.J. Torley, at least in outline. It is a fairly mundane characterization of the Aristotelian perspective, although there is much debate to this day about the subtleties and implications of this perspective.

Where Torley and I diverge markedly is on the question of the location of perceptions. We both agree that perceptions are material things (in the hylomorphic sense), but we disagree as to where they take place. I believe that this question of location of perceptions is important, and is a reflection of one of the most pervasive errors in philosophy of the mind in the modern era.

There are three locations where perceptions might take place: at the object perceived, in the sense organ, or in the brain, or any combination thereof. There is no question that perceptions occur via the object, the sense organs, and the brain. All three are necessary for perception. If all three are necessary for perception, which are the location of perception?

Aristotle didn’t explicitly locate perception at the object, although he certainly implicitly did so. His is theory of perception entails that the perception is located at the object grasped at least in the sense that it begins at the object; it does not begin in the sense organs or in the brain. Perception is not something that takes place wholly within the skin or the skull of the perceiver. The crux of Aristotle’s theory of perception is that the perceiver “is made like the object and has acquired its quality” (DA II 5). One is not made like an object nor can one acquire its quality in a Cartesian theater — where one merely watches a movie. One becomes a soldier by going to war, not by watching Saving Private Ryan. One is made like an object and acquires its quality by encountering the object, not by watching a movie about the object. The perception of an object — being made like the object — occurs at the object, not in a sense organ or in a brain.

If perception does not occur at the object — if it begins only at the sense organ or the brain — then there is no encounter between perceiver and perceived. If perception begins at the sense organ, and not at the object, then only the sensory stimulus, not the object, is perceived.

Perception encompasses the object perceived. The object of perception is that which we perceive and is at which we perceive. Our sense organs and brain are that through which we perceive.

The Cartesian/Lockean doctrine, whether the theater is in the skull or in the skin, depends critically on the reality of primary and secondary qualities. Are there genuinely objective quantifiable properties that are ontologically different from subjective qualitative properties? Aristotle knew nothing of primary and secondary properties — the concept would be foreign to him. He lumped together quantitative and qualitative properties as accidents (Categories), and made no ontological distinction between what we now call primary and secondary qualities.

Without primary and secondary qualities — a very un-Aristotelian concept — the Cartesian theater is closed for business.

In the Aristotelian view, the perception of an object is the possession of its form. This includes its accidental forms as well as its substantial form. Location is an accidental form (Organon 1b25-2a4). Thus, in my interpretation, possession of an object entails possession of its location — perception of an object occurs at the location of the object.

There are deeper problems with the notion that perception occurs only at the sense organs and brain. Let us imagine that the Cartesian theater is real and perception occurs only in sense organs and the brain. In this scenario, we only have direct knowledge of our perceptions themselves; we never have direct knowledge of the objects perceived. And in this Cartesian theater, there can be no reliable knowledge of the external world whatsoever, because any attempt at confirmation of knowledge by correlating internal perception with external reality is rendered moot by my inability to perceive the outside world directly. We are trapped inside the theater, and we can’t get out. The Cartesian theater leaves us practically and even theoretically unable to know reality. This is of course at the root of Kant’s distinction between noumena and phenomena, which is an epistemological mess made inevitable by our attendance at the Cartesian theater.

And locating perception in the senses, or in the brain and the senses, doesn’t solve the problem, it merely makes the Cartesian theater a little more spacious. Either your knowledge of the world is limited by your skull or it’s limited by your skin. Either way, you’re trapped in solipsism. The Cartesian theater prevents you from having real knowledge of the world, and consigns you to infinite regress if you try to do science or try to understand the nature of the mind.

Locating perception in the sense organs and/or in the brain is a central fallacy of modern neuroscience and philosophy of mind. The study of perception — central to cognitive science — is itself unmoored from reality by the implicit or explicit presumption of the Cartesian theater. A scientist trapped in a Cartesian theater can have no sure knowledge of external reality, which is the very object of science, and even the study of the Cartesian theater itself entails merely an infinite regress of Cartesian theaters, a Lowes multiplex of subjectivity and exclusion from reality.

Perception at a distance is no more inconceivable than action at a distance. The notion that a perception of the moon occurs at the moon is “bizarre” (Torley’s word) only if one presumes that perception is constrained by distance and local conditions — perhaps perception would get tired if it had to go to the moon or it wouldn’t be able to go because it’s too cold there. Yet surely the view that the perception of a rose held up to my eye was located at the rose wouldn’t be deemed nearly as bizarre. At what distance does perception of an object at the object become inconceivable?

Which is more bizarre — the view that perception begins at its object, or the view that perception doesn’t occur at its object because it cannot travel long distances or go to inhospitable places?

If one accepts the view that perceptions occur only in the sense organs and the brain, one can make no actual claims to knowledge about any external object of perception, or even, ironically, about one’s own perceptions if tested empirically. Infinite regress and solipsism are the curse of the Cartesian theater. It is no coincidence that epistemology didn’t emerge as a named discipline until the 19th century — it wasn’t until our general acceptance of the modernist Cartesian/Lockean separation of perceptions from reality that we came to believe that real knowledge is elusive. For the Cartesian who locates the origin of perception at the sense organs and not at the object perceived, “I think therefore I am” isn’t merely the beginning of knowledge. It’s the end of knowledge.

As counterintuitive as it seems at first, the view that perception begins at the location of the object and not in the sense organs or the brain is the only view of perception that makes any sense. It does not lock us in solipsism, cut off entirely from any direct knowledge of the world. And the view that perception occurs at the object is a perfectly reasonable interpretation of Aristotle’s dicta that the real object of perception is the object perceived, that the perceiver in a sense possesses the object perceived, that location is an accidental form possessed by the perceiver, and that the ontological distinction between primary and secondary qualities is unfounded.

The modernist Cartesian/Lockean nonsense that perceptions only begin in the sense organs or brain is difficult to get beyond. We are born in a milieu saturated with Cartesian and materialist misconceptions, and it’s hard, even for people sympathetic to the Aristotelian view, to shake free of it. Even thoughtful and very well informed Aristotelians sometimes purchase tickets to the Cartesian theater. Yet one can find the truth only if one leaves the theater and steps into the real world — where perceptions really are.

Image credit: Jennifer Garcia (Reverie) [CC BY-SA 2.5-2.0-1.0], via Wikimedia Commons.

Michael Egnor

Senior Fellow, Center for Natural & Artificial Intelligence
Michael R. Egnor, MD, is a Professor of Neurosurgery and Pediatrics at State University of New York, Stony Brook, has served as the Director of Pediatric Neurosurgery, and award-winning brain surgeon. He was named one of New York’s best doctors by the New York Magazine in 2005. He received his medical education at Columbia University College of Physicians and Surgeons and completed his residency at Jackson Memorial Hospital. His research on hydrocephalus has been published in journals including Journal of Neurosurgery, Pediatrics, and Cerebrospinal Fluid Research. He is on the Scientific Advisory Board of the Hydrocephalus Association in the United States and has lectured extensively throughout the United States and Europe.