Mind-brain dualism is the view that brain and mind are derived from entirely different kinds of things — physical stuff and mind-stuff. Dualism assumes that both kinds of stuff exist in the universe and that science has simply not yet detected and discovered the mind-stuff. Dualism feels intuitively correct to most people, as it fits with our subjective experience. But it is completely contradicted by science.
It seems to me to be very difficult to deny that consciousness is non-physical. Regardless of whether brains produce consciousness or not, it seems straightforwardly obvious that consciousness itself lacks mass or any other physical properties. This is in stark contrast to the neural correlates of consciousness. It's also very difficult to deny the existence of a mental substance. For is it intelligible to say there could be, for example, a pain without any entity undergoing that pain? Or that there can be thoughts without a thinker? So, contrary to what Ralph Lewis claims, I'm not sure if it is correct to say any assumptions are being made here. Rather, substance dualism seems to be derived from our immediately lived experience. It is for this reason that substance dualism is the commonsensical position that we are all born believing. Even most of those who emphatically reject an afterlife implicitly accept this commonsensical position.
But is substance dualism contradicted by science? Although it is true that science has not detected either this self or its conscious experiences, the failure here neither suggests anything about their existence nor does it point to a defect of science or contradict it. Science only detects the measurable or quantifiable aspects of reality. Hence, it can detect neurons firing, but it cannot detect the conscious experiences correlated with this neuronal activity. But this doesn’t mean that selves and their conscious experiences don't exist, nor that science is wrong, rather science is simply the wrong tool for the job. Compare this to the fact that a metal detector will fail to detect wood or plastic. We certainly wouldn't conclude that wood and plastic don't exist, nor that the metal detector is working incorrectly.
He also says:
There is no aspect of the mind, the personality, or the self that is not completely susceptible to chemical influences or physical diseases that disrupt neuronal circuitry.
So, how is it that scientists are so certain that dualism is false? Quite simply, because for dualism to be true, all of science would have to be false.…Dualism so fundamentally contradicts the foundations and entire accumulated evidence of modern science that in order for it to be true, we would have to start rebuilding modern science from the ground up. If dualism turned out to be true, it would also be a complete mystery or fluke as to how most of our advanced technologies (including all of our electronics) work at all, since their design and engineering are based on the very principles that would necessarily be entirely invalidated if dualism were true.
I'm going to go into a bit more detail here since this is a serious charge to make. For, if true, it places advocates of dualism firmly in the anti-science camp. But why on earth do certain materialists believe this?
From reading around, and especially reading the arguments of the physicist Sean M. Carroll (whom the author appeals to in a footnote), it seems they are convinced that science entails that the physical world is closed. This is the thesis that physical causation wholly accounts for all change in the world, including all of our voluntary behaviour and even the direction our thoughts take. This is what all forms of materialism hold, and at least interactive substance dualism contradicts this since, contrary to the materialists, those who subscribe to it believe consciousness, in and of itself, is causally efficacious. So since substance dualists usually believe in the existence of mental causes in addition to physical ones, they are committed to denying that our current laws can be completely accurate. Does this entail most of our modern technology wouldn't work, as Lewis and others claim?
Firstly,
we should remind ourselves that this contravening of physical causal
closure only occurs with the impact of consciousness on processes within
the brain. This impact will likely be minuscule, most likely on the quantum scale, and hence will be undetectable. After this initial impact by consciousness, we might suppose the usual chains of physical causes and effects
apply, cascading this initial minuscule change to larger and larger effects resulting in our voluntary behaviour. But, apart from any changes precipitated by our own voluntary activity, why on earth do they imagine that the rest of
physical reality would be affected? After all, the vast preponderance of the Universe is far removed from this initial change precipitated by
consciousness.
Hence, thirdly, and regardless of whether one subscribes to an afterlife or not, it needs to be pointed out that we immediately experience our own causal efficacy whenever we make any voluntary movement, or even when we entertain a chain of thought. And in case people don't find that convincing, I argue in this blog post in the first two sections that it is simply incoherent to suppose consciousness has no causal impact and, furthermore, that this causal impact necessarily has to be over and above physical causation.
Fourthly, our current
physics leaves out the existence of consciousness in its description of
reality (see the hard problem of consciousness) and a fortiori, it also leaves out any causal role that consciousness plays. So, this entails our
current theories simply cannot be completely accurate, at least when applied to living brains.
Ralph Lewis seems very certain of himself in the dismissal of an afterlife. But, at least in this article, it does not seem to me that he has brought up anything particularly problematic regarding either interactive substance dualism or an afterlife.