What sorts of arguments can substance dualists offer? What sorts of arguments would indicate that mind can exist independently of a physical basis? There is overwhelming evidence of the extremely sensitive dependence of every aspect of the mental on a physical basis, the brain in particular. The books of the late, great Oliver Sacks recount many cases, some amusing, some inspiring, and some tragic, showing that the most intimate and defining aspects of personality as well as the most basic experiences of perception and sensation, are fundamentally altered when brain function is changed or impaired. The ingestion of microgram quantities of lysergic acid diethylamide causes major perceptual alterations. On the other hand, lack of certain trace elements in the diet can cause major mental aberrations. For instance, lack of magnesium can cause confusion, depression, and hallucinations.

More significantly, neuroscience has made considerable progress in understanding significant aspects of human behavior in terms of brain function, as engagingly recounted in David Eagleman’s neuroscience primer, The Brain: The Story of You. For instance we now have a neurological understanding of the basis of genocide. As Eagleman reports, the human capacity for empathy is a matter of literally feeling another’s pain. When we perceive pain in another, the pain matrix of our brains is activated:

If you watch someone else get stabbed, most of your pain matrix becomes activated. Not those areas that tell you you’ve been actually touched, but instead those parts involved in the emotional experience of pain. In other words, watching someone else in pain and being in pain use the same neural machinery. This is the basis of empathy. (Eagleman, p. 143).

Unfortunately, however, our brains are also susceptible to influences that cause our empathetic propensities to be, in effect, short circuited so that they no longer influence decision making. Researchers have identified an area of the brain called the medial prefrontal cortex (mPFC) that is activated when we are thinking about persons, but is inactive when we are thinking about inanimate objects. Experiments showed that the mPFC regions became less active in volunteers who were shown pictures of homeless people or drug addicts. The consequence is dehumanization, thinking of people as objects rather than persons:

…by shutting down the systems that see the homeless person as another human being, one doesn’t have to experience the unpleasant pressures of feeling bad about not giving money. In other words, the homeless have been dehumanized: the brain is viewing them more like objects and less like people. (Eagleman, p. 155).

In this context Eagleman discusses the research of neurosurgeon Itzhak Fried who identifies what he calls “Syndrome E,” reduced emotional reactivity that is associated with acts of systematic violence. Genocides are preceded by dehumanization, the process of getting people to think of members of an outgroup as objects rather than as persons. We are now in a positon to understand, predict, and possibly control the process of dehumanization in terms of brain processes. We are coming to understand the physiological mechanisms of genocide. Highly successful research programs tend to justify the heuristic assumptions upon which they are conducted. The regulative assumption of all neuroscientific research is that brain function is sufficient for every aspect of the mental.

What, then, are the arguments that substance dualists can offer? What arguments or evidence could indicate that, despite manifold and multifarious appearances, the mental is separable from the physical and capable of operating without it? Their empirical arguments are exiguous in the extreme, consisting of little more than claims about near-death experiences (NDE’s). In 2012 I attended a conference on life after death at the New Orleans Baptist Theological Seminary. There I saw a debate between Dr. Gary Habermas, of Liberty University and well-known skeptical author Michael Shermer. Habermas claimed that there were clear instances of NDE’s that indicated the occurrence of conscious experience independently of brain processes. Habermas is a clever debater, but cleverness alone cannot transform the sow’s ear of weak evidence into the silk purse of persuasion. The odor of crackpots, cranks, and charlatans cannot be wholly cleansed from the topic of NDE’s, even when they are defended by distinguished academics. For tactical reasons then, if no other, substance dualists usually shy away from NDE’s.

Generally then, substance dualists appeal to philosophical arguments, in an effort to establish a priori the non-reducibility of the mental to the physical. A good succinct account of such an argument is posted on the site Thinking Matters by Ben Mines:

http://thinkingmatters.org.nz/2018/04/the-argument-from-consciousness-qualia/

Mines argues that there are five properties of consciousness (qualia, intentionality, privileged access, nonphysicality, and free will) that in principle elude explanation in naturalistic terms, and so indicate that the mental cannot be subsumed within a naturalist ontology. The consequences of this are seen as significant:

…if the mind cannot possibly be reduced to the brain then mind and brain are not identical. Naturalism is falsified and some form of substance dualism is implicated. And given the existence of nonphysical mental substances established by the argument, theism is an inference to the best explanation for them.

This seems a bit hasty and abrupt to me. Even if we conceded that the accepted terms of neuroscience—electrical and chemical happenings in neurons—cannot explain consciousness, could we not adopt a property rather than a substance dualism as a more parsimonious option? That is, rather than take the rather extravagant step of positing supernatural entities, we could argue that some physical things or processes have mental properties as well as physical properties. Further, it seems all too quick to say that the irreducibility of the mental makes theism the best explanation. Surely, it would be evidence for theism, or enhance to prior probability of theism, but it would be only one of numerous considerations (including negative evidence such as the problem of evil) that must be considered in assessing theism. Perhaps a demonstration of the irreducibility of consciousness would be better construed as evidence for animism, the idea that the visible realm is interpenetrated by a spiritual realm containing the spirits of animals, people, and things. This was the “primitive” ontology of our preliterate ancestors, and perhaps it would be revived in modern form.

Mines here focuses on qualia and considers arguments for their irreducibility. He adduces the familiar argument from Thomas Nagel’s “What is it like to be a Bat?” Nagel noted that bats have a capacity for echolocation that humans lack. Supposedly, their natural sonar capabilities produce within them mental representations of a quality that humans have never experienced and cannot even imagine. This means that there is something about being a bat that is forever and in principle elusive to human knowers. Even an expert in bat biology, one who knows all that there is to be known about bat brains and their echolocation mechanisms, still cannot know what it is like to be a bat. The experience of bat-ness is closed off to us. The alleged consequence is that there are therefore identifiable items in the world, e.g. first-person bat consciousness—that, in principle, cannot be understood in the third-person, objective terms of natural science. Since natural science is the only explanatory tool of naturalistic ontologies, it follows that some things cannot be explained in naturalistic terms, nor, supposedly, encompassed in naturalistic ontologies. Mines concludes:

The answer is that it [what it is like to be a bat] cannot [be known] because the task is impossible by tautology: Bat qualia can no more be instantiated in nonbat consciousness than triangularity can be instantiated in a circle. Limited to the resources of the human mind, the extrapolation to bat experience is incompleteable [sic].

Now, some philosophers, such as Daniel Dennett, dismiss Nagel’s argument as an “intuition pump” masquerading as an a priori argument. An intuition pump is just a clever rhetorical device for stimulating our intuitive propensities (Leibniz’s imaginary walk through a brain the size of a factory was another). They have rhetorical bark, but no real logical bite, Dennett holds. Naturalist philosophers tend to regard intuitions with considerable skepticism, seeing them as epistemological sirens that have an irresistible song if we listen to them, but only lure us to wreck on the reefs of ignorance.

My tendency is to admit that there are some items of knowledge that can only be had by first person experience. Something really happens to Dorothy when she steps from the sepia of Kansas into the technicolor of Oz. Her experience is different in a way that she could not have explained, even if she were thoroughly versed in the physiology of color vision, to the Dorothy that sees only the gray shades of Kansas.

However, Mines’ conclusion does not follow. An experience, per se, tells us nothing conclusive about the causal provenance of that experience, a truth that philosophers have exploited many times to their advantage. I may be having the experience of seeing my computer screen, but maybe that experience is caused by a Cartesian Demon rather than my computer screen. Maybe the tree we see in Berkeley’s quad is there because God wills that we have tree-perceptions rather than the subsistence of an actual woody, leafy entity. So, perhaps my sensations in all of their qualitative richness are caused by God, or a demon, or a soul. Or a brain.

There is nothing in the qualitative content of my consciousness that informs me that such experience could not have been physically produced. Maybe I cannot intuitively see why brain processes would cause qualia (Chalmers’ “hard” problem), but it does not follow that a brain cannot do it. So, the relevant question is not whether there are some items of knowledge that can only be had via first-person consciousness. The important question is whether first person experience can be physically caused. Why not? Nor is there any reason to think that we could not know, in detail, how it was caused. That is what neuroscience does. If neuroscience can explain how my brain produces first-person experience, then such experience is subsumable under a naturalistic ontology.

Could I have a bat’s sonar qualia? I don’t see, in principle, why not. Bats have their particular batty experiences because their brains are wired differently. But brains have an incredible degree of plasticity and if my brain could be wired to do what a bat’s brain does, and I could be given the bat’s sensory input, why couldn’t I have bat-sensations? Maybe when neuroscience is far more advanced, we will be able to customize our brains to do things and have experiences that we cannot currently do. Maybe we could see infrared and ultraviolet. Maybe we could hear the high pitches that a dog can hear or the low pitches that an elephant can. What will those experiences be like? Well, we can’t say now, but there seems to be no reason to think that we can never know.