In response to my recent article, “Science and the Soul” in Plough Magazine, a commenter raised an interesting issue about free will and the brain:

I found a puzzling fact (that seems to have been omitted from the article) which does imply the division of will. Once the patient’s brains had been split, amazingly it was discovered that each half had their own preferences, and in some case would struggle with one another for control. One of the examples shared told the story of a woman whose sides differed on their specific tastes for clothing, and each time she’d try to get dressed, her left hand would interfere and unbuttoned her shirt, as the right tried to fix the problem. Another example cited related to food, where the right hemisphere was not pleased with what the left hemisphere had been cooking and threw a vial of salt on the food, to render it useless. These examples do seem to imply that will and awareness are indeed split, and there is a struggle for power between the two hemispheres, and thus the two sides of the body. Do you have another explanation for it that would keep it compatible with your thesis of a single will?

It’s a great question. The commenter is describing alien hand syndrome. This neurological condition occasionally afflicts patients who have had split-brain surgery or other procedures or injuries that disconnect regions of the brain. They experience involuntary movements of limbs. Most commonly it is the left arm, which seems to have a mind of its own. The classic example, which the commenter mentioned, is a patient who intentionally buttons her shirt with her right hand while her left hand follows, unbuttoning her shirt, which she doesn’t intend! The predicament points to the fact that while free will is immaterial, appetite (desire) is a material power of the mind that arises wholly from brain processes.

Most of our actions are unconscious. When we walk, we move scores of muscles in very precise, coordinated ways of which we are unaware. Virtually all of our movements entail actions that are not part of our immediate consciousness—I was not thinking of flexing the flexor muscle of the distal phalanx of my left ring finger each time I typed “s” while writing this essay. Our muscles do things we don’t think about, and they often do things we don’t even intend. For example, I’m a terrible typist—my distal phalanx flexors are notoriously disobedient! Parts of our body always do things that are outside of our awareness. We couldn’t function if we had to think about them. We can, of course, bring some acts into conscious awareness by thinking about them, but it takes effort. I can’t bring some acts (the beating of my heart) into conscious awareness and control, no matter how hard I try.

It is noteworthy that our most precise and accomplished acts tend to be those of which we are unaware—a beginning pianist must think about each finger stroke as he plays, but a virtuoso plays effortlessly, without awareness of each finger movement. The virtuoso is aware of the grand theme—the beauty and passion of the music. As he gained skill over time, he became less and less aware of the movements of his individual fingers.

Unconscious acts that help us succeed are generally a sign of skill, not dysfunction. But sometimes, particularly with brain injuries, this disconnection between conscious awareness and bodily actions becomes extreme, for example, with alien hand syndrome. Instead of my left ring finger mischievously typing “w” instead of “s”, as it is wont to do, my left hand (if I have a brain injury) might unbutton my shirt when I’m trying with my right hand to button it. That would be an extreme manifestation of an ordinary characteristic of my nervous system that usually results in nothing more than typos.

But the commenter’s question is salient: Doesn’t alien hand syndrome mean that I really don’t have free will, in the sense of a single, undivided (metaphysically simple) will that is not determine by physical processes in the brain?

No, alien hand syndrome doesn’t mean that free will is not real. In fact, it clarifies exactly what free will is and what it isn’t. We have, broadly speaking, two kinds of volition. In common with animals, we have appetite. Appetite is volition that arises from material processes in the brain. Appetite may or may not be entirely conscious, but it entails motor acts and perceptions linked to specifics of the environment—a keyboard, a button, a bowl of food, or a sexually attractive person. We, along with non-human animals, experience powerful appetites arising from brain processes (neurochemicals, action potentials, and the like) all of the time. In fact, appetite is the only type of volition that non-human animals experience.

But human beings have another kind of volition as well. We have will, which, unlike appetite, does not arise from brain processes. Will follows from intellect, which is the human ability to think abstractly, without linking the thought to particular objects. I may desire an extra slice of cake (appetite), but I think about how bad that would be for my nutritional health (intellect) and decide, based on my abstract concern for my health, to forgo the cake (will). My will can override my appetites.

Because will follows on intellect, which is an immaterial power of abstract thought, will is free, in the sense that it is not determined by physical processes such as brain chemicals. Will is, of course, influenced by physical processes. If I’m really hungry and tired, I may decide to have that piece of cake anyway because my appetite has got the better of my compromised intellect. But I still chose to have the cake. My choice was not determined by chemistry, although it was influenced by chemistry.

Remarkably, the material nature of appetite and the immaterial nature of will have been observed by neuroscientists. Mid-20th century neuroscientist Benjamin Libet found that simple decisions like pushing a button were preceded by brain wave spikes, which implied a material predisposition to do a particular act. But the decision could be vetoed, without any corresponding brain wave spike, which Libet interpreted as the action of free will. The will didn’t show up on his instruments, yet it had the final say when subjects made choices.

Libet famously said that we don’t so much have free will as, more precisely, we have “free won’t.” We are beset by physical appetites and we can choose whether or not to comply with our desire. We can freely veto those appetites. Our will is immaterial, and thus free.

All of the examples of alien hand syndrome involve particular acts—a hand unbuttoning a button or reaching for an object, and the like. This splitting of volition to do particular acts is splitting of the appetite, not splitting of the will. There are no examples of splitting of the will— no examples of simultaneous distinct abstract intentions.

Now, I don’t mean that we don’t have times of indecision; of course we do. I mean that there are no examples of simultaneous distinct abstract decisions—say, to deliberately will justice and injustice at the same moment or to deliberately do differential calculus and integral calculus (one with the right hand, one with the left) at the same moment. Will is metaphysically simple, in the sense that it has no parts that can separate completely from one another. In fact, unity of will is more or less what we take to define an individual person. If there are two distinct wills, there are two distinct people. ‘Splitting of the will’ defies what we know to be true of human beings.

It is the abstract nature of will that distinguishes it from appetite and makes it free and metaphysically simple, incapable of being split. Alien hand syndrome is an example of splitting of appetite, which is a brain function driven wholly by material processes. Thus, alien hand syndrome is not an exception to free will at all. In fact, a proper understanding of alien hand syndrome helps us understand what free will really is.

Human volition entails both appetite and will. Appetite is a material tendency to act, driven wholly by the brain. Free will is the immaterial human ability to obey, or defy, appetites.

Also by Michael Egnor: Can mere products of nature have free will?

Does brain stimulation research challenge free will?

and

Is free will a dangerous myth?