Recently I got into a discussion with Gordon Hawkes on A Philosopher’s Take about the arguments and objections for substance dualism, that is, the position that there are actually two ontological substances that exist in the world: physical substances and mental (or non-physical) substances. Here’s the link to part 1, and part 2 of that author’s post series (I recommend taking a look at this group blog and see what he and others have written over there on various interesting topics). Many dualists would identify or liken this supposed second substance as a soul or the like, but I’m not going to delve into that particular detail within this post. I’d prefer to focus on the basics of the arguments presented rather than those kinds of details. Before I dive into the topic, I want to mention that Hawkes was by no means making an argument for substance dualism, but rather he was merely pointing out some flaws in common arguments against substance dualism. Now that that’s been said, I’m going to get to the heart of the topic, but I will also be providing evidence and arguments against substance dualism. The primary point raised in the first part of that series was the fact that just because neuroscience is continuously finding correlations between particular physical brain states and particular mental states, this doesn’t mean that these empirical findings show that dualism is necessarily false — since some forms of dualism seem to be entirely compatible with these empirical findings (e.g. interactionist dualism). So the question ultimately boils down to whether or not mental processes are identical with, or metaphysically supervenient upon, the physical processes of the brain (if so, then substance dualism is necessarily false).
Hawkes talks about how the argument from neuroscience (as it is sometimes referred to) is fallacious because it is based on the mistaken belief that correlation (between mental states and brain states) is equivalent with identity or supervenience of mental and physical states. Since this isn’t the case, then one can’t rationally use the neurological correlation to disprove (all forms of) substance dualism. While I agree with this, that is, that the argument from neuroscience can’t be used to disprove (all forms of) substance dualism, it is nevertheless strong evidence that a physical foundation exists for the mind and it also provides evidence against all forms of substance dualism that posit that the mind can exist independently of the physical brain. At the very least, it shows that the prior probability of minds existing without brains is highly unlikely. This would seem to suggest that any supposed mental substance is necessarily dependent on a physical substance (so disembodied minds would be out of the question for the minimal substance dualist position). Even more damning for substance dualists though, is the fact that since the argument from neuroscience suggests that minds can’t exist without physical brains, this would mean that prior to brains evolving in any living organisms within our universe, at some point in the past there weren’t any minds at all. This in turn would suggest that the second substance posited by dualists isn’t at all conserved like the physical substances we know about are conserved (as per the Law of Conservation of Mass and Energy). Rather, this second substance would have presumably had to have come into existence ex nihilo once some subset of the universe’s physical substances took on a particular configuration (i.e. living organisms that eventually evolved a brain complex enough to afford mental experiences/consciousness/properties). Once all the brains in the universe disappear in the future (after the heat death of the universe guarantees such a fate), then this second substance will once again disappear from our universe.
The only way around this (as far as I can tell) is to posit that the supposed mental substance had always existed and/or will always continue to exist, but in an entirely undetectable way somehow detached from any physical substance (which is a position that seems hardly defensible given the correlation argument from neuroscience). Since our prior probabilities of any hypothesis are based on all our background knowledge, and since the only substance we can be sure of exists (a physical substance) has been shown to consistently abide by conservation laws (within the constraints of general relativity and quantum mechanics), it is more plausible that any other ontological substance would likewise be conserved rather than not conserved. If we had evidence to the contrary, that would change the overall consequent probability, but without such evidence, we only have data points from one ontological substance, and it appears to follow conservation laws. For this reason alone, it is less likely that a second substance exists at all, if it isn’t itself conserved as that of the physical.
Beyond that, the argument from neuroscience also provides at least some evidence against interactionism (the idea that the mind and brain can causally interact with each other in both causal directions), and interactionism is something that substance dualists would likely need in order to have any reasonable defense of their position at all. To see why this is true, one need only recognize the fact that the correlates of consciousness found within neuroscience consist of instances of physical brain activity that are observed prior to the person’s conscious awareness of any experience, intentions, or willed actions produced by said brain activity. For example, studies have shown that when a person makes a conscious decision to do something (say, to press one of two possible buttons placed in front of them), there are neurological patterns that can be detected prior to their awareness of having made a decision and so these patterns can be used to correctly predict which choice the person will make even before they do! I would say that this is definitely evidence against interactionism, because we have yet to find any cases of mental experiences occurring prior to the brain activity that is correlated with it. We’ve only found evidence of brain activity preceding mental experiences, never the other way around. If the mind was made from a different substance, existing independently of the physical brain (even if correlated with it), and able to causally interact with the physical brain, then it seems reasonable to expect that we should be able to detect and confirm instances of mental processes/experiences occurring prior to correlated changes in physical brain states. Since this hasn’t been found yet in the plethora of brain studies performed thus far, the prior probability of interactionism being true is exceedingly low. Additionally, the conservation of mass and energy that we observe (as well as the laws of physics in general) in our universe also challenges the possibility of any means of causal energy transfer between a mind to a brain or vice versa. For the only means of causal interaction we’ve observed thus far in our universe is by way of energy/momentum transfer from one physical particle/system to another. If a mind is non-physical, then by what means can it interact at all with a brain or vice versa?
The second part of the post series from Hawkes talked about Occam’s razor and how it’s been applied in arguments against dualism. Hawkes argues that even though one ontological substance is less complex and otherwise preferred over two substances (when all else is equal), Occam’s razor apparently isn’t applicable in this case because physicalism has been unable to adequately address what we call a mind, mental properties, etc. My rebuttal to this point is that dualism doesn’t adequately address what we call a mind, mental properties, etc., either. In fact it offers no additional explanatory power than physicalism does because nobody has proposed how it could do so. That is, nobody has yet demonstrated (as far as I know) what any possible mechanisms would be for this new substance to instantiate a mind, how this non-physical substance could possibly interact with the physical brain, etc. Rather it seems to have been posited out of an argument from ignorance and incredulity, which is a logical fallacy. Since physicalism hasn’t yet provided a satisfactory explanation for what some call the mind and mental properties, it is therefore supposed by dualists that a second ontological substance must exist that does explain it or account for it adequately.
Unfortunately, because of the lack of any proposed mechanism for the second substance to adequately account for the phenomena, one could simply replace the term “second substance” with “magic” and be on the same epistemic footing. It is therefore an argument from ignorance to presume that a second substance exists, for the sole reason that nobody has yet demonstrated how the first substance can fully explain what we call mind and mental phenomena. Just as we’ve seen throughout history where an unknown phenomena is attributed to magic or the supernatural and later found to be accounted for by a physical explanation, this means that the prior probability that this will also be the case for the phenomena of the mind and mental properties is extraordinarily high. As a result, I think that Occam’s razor is applicable in this case, because I believe it is always applicable to an argument from ignorance that’s compared to an (even incomplete) argument from evidence. Since physicalism accounts for many aspects of mental phenomena (such as the neuroscience correlations, etc.), dualism needs to be supported by at least some proposed mechanism (that is falsifiable) in order to nullify the application of Occam’s razor.