For some reason, most of us are a lot easier on dualists — those who insist the mind is somehow independent of the brain. Granted, there's always neuroscientist and skeptic Steve Novella, who definitely doesn't pull any punches, but a firm condemnation of dualism just isn't quite as prevalent in the public community of skeptics and non-believers as arguments against evolution deniers.
Maybe it's because the mind sciences — neurobiology, neurocomputation, and cognitive science — are a bit more esoteric. They're characterized by a somewhat obscure lexicon that doesn't always lend itself to concisely packaged arguments. But that should not obscure the fact that from a scientific standpoint, there is no dispute that the mind is wholly caused by the brain. You are not going to comb through an issue of Scientific American Mind and find the latest research from dualists because, well, dualists aren't actually doing any research. That's because unlike a brain-emergent theory of mind, dualist theories of mind don't make predictions and accordingly are unfalsifiable. Instead, they live in the margins as post hoc rationalizations for data produced by the hard sciences of the mind.
Dualism is conceptually ambiguous
A common refrain from dualists is that since the mind is not material, it cannot be studied empirically. Science, they say, studies the 'natural world'. This allows dualists to have their cake and eat it, too: they can try to explain scientific data in the context of dualism without ever producing a working scientific theory that would actually generated testable hypotheses.
But this rationalization fails at a basic conceptual level. Sean Carroll concisely summarizes the problem in an op-ed for Scientific American:
Claims that some form of consciousness persists after our bodies die and decay into their constituent atoms face one huge, insuperable obstacle: the laws of physics underlying everyday life are completely understood, and there's no way within those laws to allow for the information stored in our brains to persist after we die. If you claim that some form of soul persists beyond death, what particles is that soul made of? What forces are holding it together? How does it interact with ordinary matter?And Sam Harris, in a discussion with the late Christopher Hitchens, David Wolpe, and Bradley Artson Shavit, summarized the issue on similar terms:
Science is not in principle committed to the idea that there’s no afterlife or that the mind is identical to the brain.
If it’s true that consciousness is being run like software on the brain and can – by virtue of ectoplasm or something else we don’t understand – be dissociated from the brain at death, that would be part of our growing scientific understanding of the world if we discover it.
But there are very good reasons to think it’s not true. We know this from 150 years of neurology where you damage areas of the brain, and faculties are lost. You can cease to recognize faces, you can cease to know the names of animals but you still know the names of tools.
What we’re being asked to consider is that you damage one part of the brain, and something about the mind and subjectivity is lost, you damage another and yet more is lost, [but] you damage the whole thing at death, we can rise off the brain with all our faculties intact, recognizing grandma and speaking English!
All of these discussions point to two fundamental conceptual problems with mind-body dualism:
- Dualists do not have a theory of what the mind is, or even an unambiguous description of a non-material substance
- More importantly, dualists do not have a testable hypothesis that would explain how the immaterial mind causally interacts with the physical brain — or even why it should in the first place.
The evidence is overwhelmingly on the side of a material account of the mind
Aside from the lack of empirical evidence or even a coherent theoretical structure from dualists, there are many reasons to be confident that the mind is caused by the brain.
Evidence from cognitive linguistics shows that basic conceptual systems used for reasoning are defined not just by our brains, but by our motor systems. Gestalt perception and motor schemas share neural circuitry with higher-level abstraction. From Lakoff:
• Our brains are structured so as to project activation patterns from sensorimotor areas to higher cortical areas. These constitute what we have called primary metaphors. Projections of this kind allow us to conceptualize abstract concepts on the basis of inferential patterns used in sensorimotor processes that are directly tied to the body. [Philosophy in the Flesh, Kindle location 962]Primary metaphors are such concepts as big is important (tomorrow is the big day!), love is closeness (the stress of their jobs drove the couple apart), more is up (stock prices skyrocketed!), bad is smelly (this movie stinks), etc. There are a great deal of these metaphors, and they are integral to our process of reasoning — we literally cannot reason without them.
Moreover, these metaphors have a neural grounding in what is called conflation. Lakoff, again:
In research on metaphor acquisition in children, Johnson (Al, 1997b, c) studied the Shem corpus in detail. This is a well-known collection of the utterances of a child named Shem, recorded over the course of his language development (D, MacWhinney 1995). In an attempt to discover the age at which Shem acquired a commonplace metaphor, Johnson looked at Shem's use of the verb see. His objective was to discover the mechanism involved in the acquisition of metaphor. He had hypothesized conflation as a possible mechanism, and he wanted to find out whether there is indeed a stage of conflation prior to the use of the metaphor. His test case was Knowing Is Seeing, as in sentences like "I see what you're saying." In such metaphorical examples, knowing is the subject matter. Seeing is the metaphorical source domain used to conceptualize knowledge, but it is not used literally.
Johnson discovered that, prior to using metaphor, Shem went through a stage in which the knowing and seeing domains were conflated. Since we normally get most of our knowledge from seeing, a conflation of these domains would have been expected. In such conflations, the domains of knowing and seeing are coactive and the grammar of know is used with the verb see in a context in which seeing and knowing occur together-for instance, "Let's see what's in the box." Here, seeing what's in the box correlates with knowing what's in the box. [Philosophy in the Flesh, Kindle location 633]The case for embodied cognition is vastly more complex than these few snippets can illustrate, but what's important to take from this is that the embodied account only makes sense in the framework of a physical account of the mind, and it makes direct, falsifiable predictions about the structure of our conceptual systems from the neural circuitry of our brains.
Moreover, if dualism were true, there would simply be no need to describe conceptual systems in the terms of our embodiment and our neural circuitry. As always the dualist position can be shoehorned in as part of a weaselly post-hoc rationalization of data, but dualism does not produce a theory of mind that predicts or necessitates embodied cognition — cognitive linguistics, however, does precisely that.
Science predicts a relationship between cognitive states and brain states
Another famous argument of dualists is that the relationship between brain states and cognitive states is strictly correlative, not causal. But aside from suffering from the same deficiency of being only a post-hoc rationalization of data, a scientific account of the mind predicts states of cognition as outcomes of brain states. These predictions are falsifiable, reliable, and reproducible. Steve Novella elaborates:
Not only does dualism fail to account for such correlates with any sort of theoretical framework, but there's no reason to think these predictions should hold on a dualistic account. A material account of the mind requires such predictions to be reliable and valid, as they are. Dualism is ambiguously and equivocally defined, so it's not entirely clear what a dualistic theoretical framework would require. But since no dualistic 'theory' makes testable predictions, there's no reason to think dualism would require any particular neurocognitive predictions to hold.As we have learned more and more about brain function, we have identified many modules and circuits in the brain that participate in specific functions. During the Afterlife debate I gave a few of my favorite examples.Disruption of one circuit, for example, can make someone feel as if their loved-ones are imposters, because they do not evoke the usual emotions they should feel.Disruption of another circuit can make a person feel as if they are not in control of a part of their body – so-called alien hand syndrome.A stroke that leaves the ownership module intact but unconnected to the paralyzed limb can rarely result in a supernumerary phantom limb – the subjective experience of having an extra limb that you can feel and controlled (but that does not exist).Seizures are also a profound area of evidence for the mind as brain theory. Synchronous electrical activity in particular parts of the brain can make people twitch and convulse, but also experience smells, sounds, images, feelings, a sense of unreality, a sense of being connected to the universe, an inability to speak, the experience of a particular piece of music, a sense of deja vu, or pretty much anything you can imagine. The subjective experience depends on the part of the brain where the seizure occurs.There is also copious evidence from strokes and other forms of brain damage. As a practicing neurologist I can examine a patient with a stroke and with a high degree of accuracy predict exactly where the lesion will be in the brain on subsequent imaging. Everything you think, do, and feel has a neuroanatomical correlate in the brain, and if that function is altered or not working, that will predict where the lesion can be found.
Worst of all for dualism is perhaps the most obvious problem: cognitive states have never been observed to occur without brain states. We cannot communicate with dead people. When someone has suffered severe brain damage — via a stroke, accident, or some other misfortune — specific and often counter-intuitive changes to personality, memory, awareness, empathy, or communication may be adversely affected. Not only has a neurocognitive model of the mind been able to successfully predict these cognitive states, but they've been able to show with great detail the biological mechanisms at play.
The last bastion for dualism lies not in science, but in classical philosophy. As the theologian Edward Feser claims, "The mind knows itself directly, without the mediation of a mental image or any other representation." Cognitive science has shown this claim to be unequivocally false. You have absolutely no knowledge of or choice in the formation of the metaphors that form the structure of your reasoning — and the embodied, metaphorical structure of reasoning could not have been predicted by philosophers. Lakoff, again:
[There] is no Cartesian dualistic person, with a mind separate from and independent of the body, sharing exactly the same disembodied transcendent reason with everyone else, and capable of knowing everything about his or her mind simply by self-reflection. Rather, the mind is inherently embodied, reason is shaped by the body, and since most thought is unconscious, the mind cannot be known simply by self-reflection. Empirical study is necessary. [Philosophy in the Flesh, Kindle location 80]A neurocognitive account of the mind is robustly supported by scientific data that spans multiple interrelated disciplines. It's comprised of sound theoretical models that have successfully and reliably made falsifiable predictions. Dualism trudges on, clinging desperately to the coattails of scientific progress with post hoc rationalizations of scientific data, most likely spurred by fear of facing the entailments of a successful scientific theory of mind: souls probably do not exist, and when you're dead you're gone forever. But as Carl Sagan famously said, "It is far better to grasp the universe as it really is than to persist in delusion, however satisfying and reassuring". Let's stop treating dualism as anything other than the nonsense that it is — an antiquated folk theory of mind that belongs in the dustbin along with young-Earth creationism and intelligent design.