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A battle royal over split-brain patients has been raging on a post at Uncommon Descent for the past four weeks. I was unaware of this vigorous debate until a couple of days ago, as I’ve been working on several posts of my own, which will (hopefully) be up soon. However, after having viewed the comments on the split brain thread, I’ve decided to make my own contribution to the debate, as someone who has a long-standing interest in the mind-body problem.
How it all started
Over at The Skeptical Zone, KeithS threw down the gauntlet in a post titled, Split-brain patients and the dire implications for the soul (June 22, 2013). I’ll quote a brief excerpt here:
There is a procedure, the corpus callosotomy, that disconnects the two hemispheres so that epileptic seizures cannot spread from one to the other. The hemispheres are only disconnected; neither is removed. This operation contains the seizures, dramatically improving the patient’s quality of life, but it also severs the path through which the hemispheres normally communicate. The results are fascinating, and they’re not very friendly to the dualist position:
a. In experiments with split-brain patients, it’s possible to pass information to one hemisphere but not the other. The left hemisphere literally doesn’t know what the right hemisphere knows, and vice-versa.
If there were a single, immaterial mind, it would know what both hemispheres know. Clearly, this doesn’t happen…
b. The left hemisphere controls the right half of the body, and vice-versa. When the connection between the two is cut, this results in bizarre behaviors indicating the presence of two “wills” in the same skull.
One patient was seen to pick up a cigarette with her right hand and place it in her mouth. Her left hand plucked it out and threw it away before the right hand could light it.
In another case, a man attacked his wife with one arm while defending her with the other.
If a single immaterial mind were running the show, this would not happen. How do you explain this within the dualist framework?
KeithS then drew the attention of Uncommon Descent readers to his post in a comment on Denyse O’Leary’s post, Why materialist neuroscience must necessarily remain a pseudo-discipline (June 24, 2013). In a subsequent comment, KeithS then set forth his assumptions as follows (I’ve amended the numbering that was in the original post):
Assume that:
1. There is an immaterial soul.
2. The immaterial soul is the seat of knowledge.
3. The immaterial soul is the seat of the will.
4. The immaterial soul initiates voluntary actions.
5. The immaterial soul receives information from both hemispheres.
6. The immaterial soul sends commands to both hemispheres.
If one makes all of these assumptions, then it id indeed true that dualism is in trouble. However, no dualist that I know makes all of these assumptions.
There are many kinds of dualism
Before I go on, however, I’d like to correct a common error. Many people seem to be under the impression that there are two and only two kinds of dualism: first, the substance dualism widely attributed by Descartes, who (according to many scholars) viewed mind and body as two distinct things that interact with one another; and second, the property dualism espoused by certain modern philosophers (e.g. Thomas Nagel and Jaegwon Kim), who say that the human brain has both physical properties (e.g. its weight and color) and non-physical properties (e.g. the sensations experienced by the owner of the brain in question, as well as his/her beliefs and desires), and that although the brain’s non-physical properties are emergent phenomena that are incapable of being explained in purely physical terms, they nonetheless supervene upon these physical properties, which means that they have no genuine independence of their own. Professor William Dembski has done an excellent job of exposing the inadequacies of property dualism from a theistic standpoint in his two essays, Converting matter into mind and Conflating matter and mind, so I shall say nothing more about this kind of dualism here.
There are, however, two intermediate versions of dualism between substance and property dualism, which KeithS appears to be unaware of. I’ll call them Version A and Version B for now. According to both versions, mind and body (or rather, soul and body) are not two things; rather, the human person is an essential unity. On both versions, the soul of an organism – be it a microbe, plant, fungus or animal – is simply its underlying principle of unity or form, by virtue of which it is (a) one organism, and (b) an organism of a particular kind. The human soul can thus be defined as the form of the human body – i.e. that by virtue of which my body is a human body, and not the body of another animal (say, a chimpanzee). The attribute which distinguishes the human soul from other animal souls is its ability to reason. However, the human soul’s ability to reason does not distinguish us from the animals; rather, it distinguishes us as animals. To be a human being is simply to be a rational kind of animal.
According to bother Version A and Version B, human beings are essentially animals, who are nonetheless capable of performing two distinct kinds of acts, or operations: rational acts such as reasoning, understanding, making free choices, and being charitable towards other people, which are in some way immaterial; and material acts such as feeding, growing, sensing, imagining, remembering, feeling, and moving. Because of the essential unity of the human person, even these material acts are often performed in a distinctively rational manner, which is why there is a distinctively human way of eating, for instance, that marks us out from all the other animals: we insist on observing certain customs (table manners) when we eat, we divide our meals into sequential stages (courses) and we also plan our meals in advance.
It should be noted that memory is viewed as a bodily capacity on both versions of dualism being discussed here. Neither account envisages us as having an “invisible information bank” in an immaterial soul, where we keep our memories. Memories, on both accounts, are stored in the brain.
On both of these versions of dualism, bodily acts are also acts of the soul, as the soul is essentially the form of the body, and not some detached entity piloting the body, as a demon might do if it were possessing someone. Thus when I eat an apple, it is I who decides to eat the apple, and it is I who reaches out, puts it in my mouth, chews it and swallows it. These actions are all attributable to one person.
Where the two versions of dualism differ is on the question of whether the soul can be legitimately said to interact with the body. On Version A it can, and on version B it can’t.
According to Version A dualism, whenever we perform voluntary actions, our immaterial mental acts of thinking and choosing actually make our bodies move – presumably by acting on some part of the brain, which in turn triggers the nerve signals that move our limbs. Thus our bodily acts are controlled by our immaterial thoughts and choices. Since this version of dualism claims that persons control their bodies by performing certain immaterial operations, I’ll call it thought control dualism. It is the version of dualism which I espouse.
Version B dualism, like Version A, affirms that intellectual acts of understanding cannot be equated with any kind of bodily acts or processes. However, Version B differs from Version A, in that it denies that my acts of will make my body move, in voluntary actions. My acts of will explain why my body moves, when I want to do something: that is, they account for its finality. And of course, they give my act of moving its distinctively human character, or form. But these acts are not an efficient cause of the body’s voluntary movements: they don’t make the body move. As Professor Edward Feser, who is a leading exponent of Version B, puts it:
The soul doesn’t “interact” with the body considered as an independently existing object, but rather constitutes the matter of the human body as a human body in the first place, as its formal (as opposed to efficient) cause… As I move my fingers across the keyboard, then, … the neuromuscular processes are by themselves only the material-cum-efficient causal aspect of a single event of which my thoughts and intentions are the formal-cum-final causal aspect. (Italics mine – VJT.)
More recently, Professor Feser has stated that when I perform a voluntary action, my decision and the neural activity that makes my limbs move are not “two competing candidates for efficient cause,” but are instead “two aspects of a single efficient cause, just as the meaning of a sentence and its physical realization are two aspects of one thing.” However, Feser also insists that “intellectual operations do not involve a bodily organ,” which “entails that that which carries out these operations, the human soul, must ‘subsist’ apart from the body; it isn’t a mere accident or attribute of the body.”
Since Feser acknowledges the immateriality of the intellect, but characterizes its role in human action in formal-cum-final causal terns rather than efficient causal terms, I propose to refer to his version of dualism as formal-final dualism.
It should be noted that while the two versions of dualism being compared here can both be described as hylemorphic, they are based on slightly different conceptions of an organism’s form. According to Professor Feser’s formal-final dualism, form follows function: an organism’s form is determined by its built-in goals or ends, and given the ends, just as a knife’s form is determined by its function of cutting (Aquinas: A Beginner’s Guide, Oneworld Publications, Oxford, 2009, pp. 18-19). But according to the thought control dualism which I espouse, a thing’s form is not a simple consequence of its having certain specific ends. There is more to form than finality. The body of an organism also exhibits a nested hierarchy of control (organism: organ systems: organs: tissues: cells: organelles), and an organism’s form cannot be adequately characterized without specifying this hierarchy.
I personally believe that my thought control dualism is closer in spirit to the thinking of Aquinas and the later Scholastic philosophers than the formal-final dualism advocated by Professor Feser; however, Feser strongly disagrees with me on this point, so I’ll say no more about that in this post.
Finally, I should say a little about substance dualism. Perhaps the most sophisticated modern defense of this view can be found in The Self and Its Brain, by Karl Popper and John C. Eccles (Springer, 1977, hardback; Routledge, 1984, paperback). Actually, Popper and Eccles are trialists: in addition to a World 1 of physical objects and a World 2 of states of consciousness, they also posit a World 3 of culture, knowledge and language, created by human beings. All three worlds interact. However, Eccles’ account of the mind is a dualistic one. According to Eccles, the self-conscious mind interacts with both hemispheres of the brain, but principally with the dominant hemisphere of the brain (the left hemisphere, in most people), which it controls. The minor hemisphere (usually the right hemisphere), is highly skilled in certain ways, and capable of some degree of insight and intelligence, but not (generally speaking) proper language: it can recognize no more than a few words at a time.
How dualists would respond to KeithS’s assumptions
We can now address the assumptions made by KeithS in his discussion of split-brain patients, and compare what substance dualism, thought control dualism and formal-final dualism have to say about them.
1. There is an immaterial soul.
This is true on all three versions of dualism being considered here, although they would explain the soul’s immateriality differently. Only according to substance dualism is the immaterial soul viewed as something separate from the body. On the other two versions, the soul is capable of performing immaterial acts of thinking in addition to the essentially embodied acts that it performs.
2. The immaterial soul is the seat of knowledge.
A substance dualist would say yes. A thought control dualist and a formal-final dualist would say that the immaterial soul is the seat of understanding, and that the soul knows, but they would also add that knowledge is not stored “offline” in some immaterial data bank. Because the human person is an essential unity, it is hardly surprising that under normal conditions I am able to access the memories stored in my brain. A thought control dualist would add, however, that the reason why I am able to access these memories “at will” is that God has made me in such a way that my brain is responsive to my acts of will, when it is functioning normally. A formal-final dualist would say that there literally is no “how” involved when I access these memories; I “just do,” because they are my memories, and that’s all we need to say.
3. The immaterial soul is the seat of the will.
A substance dualist such as Eccles would have no trouble with this statement: he would say that intentions belong to the inner sense in his “World 2.”
A thought control dualist would say that my acts of will are immaterial acts which can be ascribed to my soul but not my body, and that typically, whenever I decide to do something, my acts of will move a certain area in my brain, which initiates certain nerve signals that cause my limbs to move. (I’ve previously explained how this happens without violating the laws of physics in my posts, Is free will dead? and How is libertarian free will possible?)
A formal-final dualist, on the other hand, would say that acts of will are one and the same as the neuronal movements which cause my limbs to move, but viewed under an immaterial, formal-cum-finalistic aspect. That is, acts of will are not disembodied acts which make the brain or any other part of the body move.
4. The immaterial soul initiates voluntary actions.
See above. A substance dualist and a thought control dualist would say that the soul executes non-bodily acts of will, which make certain neurons in the brain move in a particular way, which in turn causes voluntary body movements. A formal-final dualist would say that voluntary bodily movements are simply those which we perform willingly.
5. The immaterial soul receives information from both hemispheres.
6. The immaterial soul sends commands to both hemispheres.
According to Eccles, who is a substance dualist, the soul communicates with the body directly, mainly (and after a brain bisection, exclusively) via the dominant left hemisphere.
A thought control dualist would also maintain that the soul receives (or more properly, abstracts) information from the brain, and that it sends commands to the brain. Once again, because there is a multi-level hierarchy of control when it comes to motor movements, a thought control dualist would have no reason to regard both hemispheres of the brain as equally privileged, in their relation of the soul’s disembodied executive commands.
A formal-final dualist, on the other hand, would say that the whole enterprise of viewing the soul as communicating with the hemispheres of the brain is a fundamentally wrong-headed one. Rather, we should say that acts of the will are simply those acts which cause limb movements, viewed under their formal-cum-finalistic aspect.
So what happens after a brain bisection? Stay tuned for the next exciting episode! In the meantime, here’s some reading to whet readers’ appetites: Eccles (The Human Psyche 1977-1979. The Gifford Lectures, Lecture 1: Consciousness, Self-consciousness and the Brain—Mind Problem and The Self and its Brain (excerpts). Here’s an interesting article on The Unity of Consciousness in The Stanford Encyclopedia of Consciousness, and here’s Thomas Nagel’s article, Brain Bisection and the Unity of Consciousness in Synthese, 22: 396–413 (1971). I’ll be back tomorrow.