By James S. Spiegel

When it comes to the nature of the mind, philosophers tend to fall into one of two camps: mind-body dualism and physicalism. Mind-body dualists affirm that human beings are composed of both a material body and a supernatural aspect—the soul. Historically, Christians have favored this perspective, and it was the dominant view in the West until the mid-twentieth century. The last few decades, however, have seen the rise of physicalism, the view that everything in the universe, including human consciousness, can be fully described in terms of physics.

Mind-body dualism is distinguished by the claim that there is something more to mind than matter, namely an immaterial soul. (In the following discussion, we will use the terms “mind” and “soul” interchangeably.) Mind-body dualists maintain that body and soul are two distinct entities or substances.
Hence, the view is also called substance dualism. The chief modern proponent of substance dualism was René Descartes (1596-1650), but the history of substance
dualism is ancient, tracing back to Socrates and, in theological history, to the Old Testament. Substance dualists agree that the basic facts of consciousness cannot be fully accounted for in physical terms. So, they insist, human nature must be supernatural as well as material.

Arguments for Mind-Body Dualism

Dozens of arguments have been offered by philosophers in defense of mind-body dualism, but a few of these have been especially influential. In the early modern
period, Descartes proposed a multi-pronged argument for dualism in his Meditations. He argued that the mind and body must be separate substances because of their very distinct properties. For one thing, he noted, the mind is invisible, while the body is visible. And the essential activity of the mind—thinking—is a wholly private act, while the body’s doings are always publicly observable. Secondly, the mind is unified in a way that the body is not. As Descartes puts it, “there is a great difference between the mind and the body, in that the body, from its nature, is always divisible and the mind is completely indivisible.”1 Thus, we talk about body “parts” but not parts of the mind, which Descartes takes to be a sign that they are distinct entities.

Both aspects of Descartes’ argument may be challenged. First, even though the mind’s operations are invisible, it does not follow from this that the mind is a separate substance from the body. Perhaps the mind is simply a feature or consequence of the brain’s operations. One might affirm this while still admitting the privacy of mind. As for Descartes’ indivisibility claim, many findings in the fields of psychology and neurophysiology would challenge this idea. For example, multiple personality disorders appear to provide direct support for the mind’s divisibility, as do split-brain experiments on epileptics, which show that distinct domains of awareness can be distinguished within the same person. Even in the psychologically healthy, many argue that the multiple functions of the mind suggest mental compartmentalization.

Although Descartes’ defense of mind-body dualism has proven to be flimsy, several other arguments have been proposed which are not so easily dismissed.

    1. The Argument from Subjectivity. Several years ago the philosopher Thomas Nagel wrote an influential essay entitled “What is it Like to be a Bat?”2 Nagel pointed out that what essentially characterizes consciousness is first-person subjectivity. In other words, regarding any mind we can reasonably say there is something that it is like to be that thing. We can say this about people and even an animal such as a bat, whereas it does not make sense to ask what it is like to be a rock or a shoe. In other words, we recognize that animals like bats have subjective experiences even if we do not happen to know what those experiences are like. We also know that no physiological description of a bat’s inner life could capture what that is like. Subjectivity necessarily eludes even the most rigorous description of brain processes. So the most exhaustive account of, say, a bat’s neurological sonar mechanisms would not bring us any closer to understanding what it is like to be a bat. This is because such descriptions are necessarily third person in nature. To ask “what is it like to be X?” is to inquire about a particular first-person experience. And no third-person (or “objective”) description could ever provide that. This means that when it comes to minds there is something about them over and above the physical.
    2. The Argument from Qualia. When you look at an apple, hear a siren, or feel a tickle, what you experience are certain qualities or “qualia” as philosophers have come to call them. All of our perceptual experiences are laden with qualia, including colors, tastes, smells, sounds, and feelings. Since qualia are such a constant part of our conscious lives, we might overlook the fact that these, too, cannot be accounted for on a physicalist view of human nature. As philosopher Frank Jackson pointed out in another landmark article, no description of the brain could possibly capture this aspect of perceptual experience.3 Jackson offers an intriguing thought experiment to drive home his point:               Mary is a brilliant scientist who is, for whatever reason, forced to investigate the world from a black and white room via a black and white television monitor. She specializes in the neurophysiology of vision and acquires, let us suppose, all the physical information there is to obtain about what goes on when we see ripe tomatoes, or the sky, and use terms like ‘red’, ‘blue’, and so on. She discovers, for example, just which wavelength combinations from the sky stimulate the retina, and exactly how this produces via the central nervous system the contraction of the vocal cords and expulsion of air from the lungs that results in the uttering of the sentence ‘The sky is blue’. . . . What will happen when Mary is released from her black and white room or is given a color television monitor? Will she learn anything or not?4The obvious answer to Jackson’s concluding question is “yes”—Mary will learn what it is like to see color! So the point here is that even a complete comprehension of the facts of the physical world, most pertinently the brain, cannot capture what it is like to have a perceptual experience of qualia such as color. This, again, shows that there is something more to mind than physical realities.
    3. The Argument from Intentionality. Take a moment and think of your mother. Are you doing so right now? Good. Now notice something about that thought. It has a quality that philosophers call “intentionality.” That is, your mental state is about something, or in this case someone—your mom. Although this is another feature of the mind that is easy to overlook (because it is such a routine part of our lives), it is noteworthy that mental states refer to things outside themselves. Thoughts of your mother, LeBron James, or the White House transcend themselves and even your own mind, as they refer to particular men, women, or objects. This quality of “aboutness” is yet another crucial feature of mind that distinguishes it from physical objects, as physical objects do not refer outside themselves in this way. Physical objects can have many different relations to one another. They can be “on top of,” “next to,” “underneath,” etc. But they cannot refer to or be “about” one another. Another way of putting this is to say that mental states have semantic content. They carry meaning, while mere physical objects do not, no matter how complex in composition or function they might be. This, of course, includes the brain. Therefore, mental states, and the mind itself, must be distinct from the brain.
    4. The Argument from Near Death Experiences. Research on “Near Death Experiences” (NDEs) has exploded in recent years. NDE scholars5 have documented thousands of cases in which persons testify to having experiences apart from the body while “dead.” But NDE claims remain controversial because of dubious methodologies employed by some researchers as well as the bizarre nature of many NDE testimonials. Despite the limits and pitfalls of NDE research, the data are a potentially rich resource of evidence for dualism, since the truth of any single NDE report would confirm that there is more to human beings than their physical bodies.The most common accounts by those who report NDEs include hovering above one’s body, heightened awareness of one’s surroundings, traveling through a tunnel or passageway, seeing a light, feelings of peace and contentment, reentering one’s body, and a subsequent change of life perspective (e.g., losing the fear of death). Less common,u but still frequent, are reports of a life review, meeting other persons or supernatural beings, and encountering beautiful scenery.NDE evidence takes two basic forms. There are direct testimonies and corroborated accounts, elements of which are verified by third parties. Thousands of individuals report having had NDEs—5% of those questioned on the subject in a 1982 Gallup poll—and their accounts demonstrate an extraordinary uniformity (the “core” account outlined above). But among the most persuasive are the accounts of children.6Here is an example of an NDE report which features both a direct testimony and corroboration:I began bleeding badly after the birth of my daughter and I was instantly surrounded by medical staff who started working on me. I was in great pain. Then suddenly the pain was gone and I was looking down on them working on me. I heard one doctor say he couldn’t find a pulse. Next I was traveling down a tunnel toward a bright light. But I had to go back. Then I met a dear friend, a neighbor from a town that we had left. He also told me to go back. I hit the hospital bed with an electrifying jerk and the pain was back. I was being rushed into an operating theater for surgery to stop the bleeding. It was three weeks later that my husband decided I was well enough to be told that my dear friend in that other town had died in an accident on the day my daughter was born.7

      NDE testimonies such as these invite commentary and speculation, but the feature of these accounts that I want to highlight here is the wide range of mental operations involved. The subjects report having sensory perceptions—seeing objects, hearing noises and conversations, and even something like tactile impressions, such as a feeling of lightness. They also report cognitions of various kinds during the NDEs, as they reason, make judgments, and express wonder about their experience. Finally, the subjects have emotions, sometimes very intense in nature.

      Again, if any one such account is true, then it follows that mental events can occur independently of the brain. And if this is so, then there is something more to human beings than our physical bodies, which confirms the truth of dualism.

      Criticisms of Dualism
      The arguments from subjectivity, qualia, intentionality, and NDEs are compelling to many critics of physicalism. Nonetheless, physicalism remains the dominant view among philosophers of mind today. Why? One reason is that mind-body dualism suffers from two significant problems which many believe have yet to be solved. One is the problem of making sense of the causal interaction between mind and body, and the other regards the dualist’s apparent violation of Ockham’s razor. We will discuss the second of these first.

      1. The Problem of Causal Overdetermination. Brain events can always be traced back to prior physical causes. When I look at an elephant, an image forms on my retina, triggering other events within my eye, which result in a neural transmission to the visual center of my cerebral cortex, resulting in my experience of seeing a large, grey mammal. Now if mind-body dualism is correct, then at what point does the soul get involved in such a mental event? It appears that wherever the soul’s activity enters the causal nexus there will be redundant causal activity, for there will be two causal streams (one mental and the other physical) culminating in one and the same physical event. Thus we are left with one unnecessary causal explanation and a violation of Ockham’s razor (i.e., other things equal, the simplest explanation is to be preferred). Theoretical parsimony would dictate that one of these causal powers be eliminated from our account of perception (and our account of consciousness generally). And since we know that the brain is involved in human thought and action, it appears that it is the concept of the soul which should be eliminated.
      2. The Interaction Problem. Another problem pertains to an apparent contradiction between traditional mind-body dualism and one of the laws of physics. The first law of thermodynamics (the law of energy conservation) says that energy is neither created nor destroyed. But how can the soul causally affect the body without creating energy? The dualist could simply insist that souls do create energy. But there is no empirical support for this claim, and there is a strong presumption against it, since the law of energy conservation is one of the most fundamental laws of physics. Anyway, whatever solution the dualist might propose leads back to an even more fundamental difficulty: How can material and non-material substances causally interact at all? In the three and half centuries since Descartes’ demise, mind-body dualists have had a difficult time in narrowing, much less closing, this ontological gap. Yet this is crucial if any sense is to be made of the notion of causal interaction as it applies to mind and body.

      The majority opinion among dualists is that mind and body are indeed causally interactive. That is, mental operations are caused by the body (brain), and bodily movements are caused by mental operations. This version of mind-body dualism is known as interactionism. Interactionists tolerate the above problems because their view accommodates what to them seems an obvious truth, namely that body stimuli, such as tickling or pricking the skin, cause mental states, such as pleasure or pain. But, again, how can material and nonmaterial substances causally interact? To circumvent this problem, some dualists prefer to deny that body and soul causally interact. They embrace the view known as occasionalism, which maintains that the body and soul are causally independent. Mental operations are the activity of soul alone, though they are (typically) associated with brain and other bodily activity.

      So how does the occasionalist account for the apparent interaction between mind and body? According to the early modern occasionalist Gottfried Leibniz (1646-1716), this appearance is due to the fact that God has coordinated mental and physical events such that body (brain) activities occur on the “occasion” of certain mental states (such as thoughts or choices) and mental states (such as sensations) occur on the “occasion” of certain bodily states (such as hand or eye movement).8 Although occasionalism seems counter-intuitive, it is noteworthy that it is immune to both of the above criticisms. By denying any causal interaction between mind and body, not only does occasionalism avoid the interaction problem but it also avoids the problem of causal overdetermination and any violation of the law of energy conservation. Despite these merits, occasionalism remains a minority view among mind-body dualists.

      All things considered—given the facts of subjectivity, intentionality and phenomenal qualia, the besetting problems with physicalist theories, mindbody dualism is the most reasonable position regarding the nature of the mind. There remain problems with dualism, of course. But these are not significant enough to warrant abandonment of this view. If anything, theyu should motivate further philosophical exploration into dualist theories of mind, including careful continuation of the debate between interactionist and occasionalist versions of the theory.

      James S. Spiegel (Ph.D.) is Professor of Philosophy at Taylor University. He is author of numerous books and articles including (with Steven B. Cowan) The Love of Wisdom: A Christian Introduction to Philosophy (Broadman-Holman, 2009).


      1 René Descartes, Philosophical Essays, trans. Laurence J. Lafleur (New York: Macmillan, 1964), 139.
      2 Thomas Nagel, “What is it Like to be a Bat?”
      The Philosophical Review 83 (1974): 435-450.
      3 See Frank Jackson’s “Epiphenomenal Qualia,”
      Philosophical Quarterly 32 (1982): 127-136.
      4 Ibid., 130.
      5 Prominent NDE researchers include P. M. H. Atwater, Peter Fenwick, Bruce Greyson, Janice Miner Holden, Alan Kellehear, Elisabeth Kubler-Ross, Raymond Moody, Melvin Morse, Maurice Rawlings, Kenneth Ring, George Ritchie, Michael Sabom, Brad Steiger, and Cherie Sutherland.
      6 For NDE studies focused on children’s accounts see Elisabeth Kubler-Ross,
      On Children and Death (New York: Macmillan, 1983); Melvin Morse and Paul Perry, Closer to the Light: Learning from Children’s NearDeath Experiences (New York: Villard, 1990); and P. M. H. Atwater, The New Children and Near Death Experiences (Rochester, Vermont: Bear and Company, 2003).
      7 Melvin Morse and Paul Perry,
      Transformed by the Light (New York: Villard, 1992), 114-115.
      8 In addition to Leibniz, this view was held by Mohammed al Ghazali, Nicolas Malebranche, George Berkeley, and, perhaps, Jonathan Edwards—all took a strong view of divine sovereignty and affirmed some form of metaphysical idealism which affirms that the physical world is mind-dependent.

(First published in the Areopagus Journal Nov/Dec 2008 Vol. 8 No. 6 The Mind Body Problem)