# Substance Dualism (Part 2 of 2) [HD]

## Метаданные

- **Канал:** QualiaSoup (archive)
- **YouTube:** https://www.youtube.com/watch?v=RZTCK8ZluEc
- **Источник:** https://ekstraktznaniy.ru/video/32201

## Транскрипт

### Segment 1 (00:00 - 05:00) []

Using terms like 'physical' or 'mental' can mislead us into thinking we must be dealing with a grand division of entities rather than something more subtle, like a shift of perspective. But let's consider this scene: someone says they want to move their arm, then their arm moves. From an external viewpoint, brain activity associated with decision-making leads to the chain of neuromuscular activity that results in the movement. The actor, from an internal viewpoint, can report experiencing a decision to move as well as the sensations of movement though how the movement is taking place never enters awareness. The moving arm itself is obviously observable from both viewpoints. This gives us two complementary accounts of the same event. There's what the brain and body are doing and how they're doing it from a third-person perspective; and what the experience of using and being a brain with a body is like from a first-person perspective. The dualist account of this scene typically confuses the two perspectives by attributing an experience with the power to cause movement. Elizabeth Valentine points out that in cases of apparent interaction we simply choose to focus attention on one aspect of the cause and the other aspect of the effect. If we say psychological stress caused a physical ulcer this doesn't rule out there being some unmentioned physiological state correlated to the stress. Max Velmans has also written about this 'perspectival switching' explaining that when we say a mental event caused a physical event we're starting with an event viewed from a first-person perspective and switching to how things appear from the third-person. As Velmans explains, both perspectives can have value (in medical diagnosis, for example where both the patient's location of pain *and* a bodily exam can be helpful). But realising when we're switching stops us misidentifying causation. And this helps us untangle the dualist interaction paradox: the problem of explaining how a mysterious non-physical substance interacts with physical stuff dissolves if all we're dealing with is one substance viewed through different, complementary perspectives. Dualists who argue for the indivisibility of consciousness are contradicted by research on split-brain patients. These are people who have undergone surgery to sever the corpus callosum which connects the two cerebral hemispheres. This operation relieves severe epilepsy by confining the abnormal electrical activity that causes seizures to one hemisphere. But it does leave the hemispheres functionally separate. Each hemisphere controls the opposite hand and processes information from the opposite side of the visual field. So when split-brain patients face a screen, fixating on a central point images flashed on the screen's left side will be registered by the right hemisphere. And vice versa. If two different images are shown, one on each side of the screen and subjects are then asked to describe what they've seen, in most cases they'll describe only the image flashed to right side of the screen, registered by the left hemisphere because, for most people, it's this hemisphere that controls language. But if asked to use the left hand to point at what they've seen they'll point only at the image from the left side of the screen registered by the right hemisphere, which controls the left hand. They'll be unable to explain why they pointed at the image, though because the part of them that can speak isn't aware of what the right hemisphere saw. This divided awareness we see when a brain is divided is consistent with consciousness having some basis in the physical brain. But it directly contradicts the dualist notion of an indivisible, non-physical consciousness. Plantinga tries to defend dualism with a thought experiment involving brain halves. He asks us to imagine one of his brain hemispheres (H1) doing all the work his whole brain normally does while the other hemisphere (H2) is dormant. At midnight, all brain data are transferred from H1 via the corpus callosum to the dormant H2, which takes over all operations of the body. H1 then gets replaced by a new, identical hemisphere (H3) into which H2's data are transferred. Plantinga says that if H1 and H2 are then destroyed his brain would be destroyed but he would continue to exist. But we know why he'd continue to exist: he's just told us his brain has been replaced by a hemisphere capable of taking over all brain operations. At no stage in this curious scenario is Plantinga left with no brain. Only *disused* brain matter gets destroyed. Like Swinburne's thought experiment in the previous video of his brain being split into two bodies this scenario is a red herring that requires no non-physical substance. On the contrary, the only indicator of Plantinga's continued existence in this thought experiment is physical data transfer between brain halves capable of taking over all operations. Unwittingly, the one thing to which Plantinga attributes his existence here is a fully functioning, physical brain. In another Plantinga thought experiment all of his body parts are rapidly replaced by other body parts. If the old parts are destroyed Plantinga declares he would then exist at a time his body doesn't. But, again, that's utterly misleading.

### Segment 2 (05:00 - 10:00) [5:00]

He's just told us his body has been replaced. The replacement *is now his body*. All Plantinga is really saying here is that his *replacement* body exists at a time when his *old* body has been destroyed. If we rapidly replace the parts of any object, destroying the old parts it's trivially true that the replacement parts will exist at a time when the old parts are destroyed Say we have a machine which, over time, has every atom replaced while remaining fully functional. Then we reassemble the discarded atoms, ending up with two machines. However much we discuss whether the machine is the same machine at different stages of replacement etc. none of that discussion forces us to propose a 'non-physical' substance to account for the machine's continued functioning during its gradual replacement. That continuity results from the physical maintenance of its functioning parts. Likewise, human cell replacement is a *physical* process that helps maintain our continuity of being. The functioning and appearance of body parts can remain virtually unaltered for years despite radical changes at the cellular level. The fine detail of fingerprints can remain identifiable over decades. No non-physical substance is needed to explain these continuities. If normal cells die without being replaced or they're replaced by defective cells that's when continuity suffers. This is especially noticeable in brain cells. Degenerative diseases like advanced Alzheimer's can be so devastating to cognitive functioning that sufferers are often described by those who've known them as mere 'shells'. Certain brain traumas lead to unusual aggression or disinhibition. Clearly, it's the *type* of change that matters. Change, in and of itself, does not inevitably prevent continuity. Dualists who say a non-physical substance maintains certain continuities in a physically changing body are challenged by discontinuities associated with physical brain damage. If the mind is separate from the brain the specific mental impairments we see after damage to specific brain structures become problematic. The intimate correlation between physical injury and impairment to our conscious experience is especially inconvenient for those who claim that consciousness can survive bodily death. Let's be clear, if the sense organs for sound and vision are destroyed in an otherwise healthy body no 'immaterial back-up system' kicks in, allowing us to see or hear again. If we destroy the senses, one by one we quickly find ourselves unable to perceive anything about our surroundings or even our own bodies. We move into perceptual blankness. If our entire bodies are destroyed what exactly is it that's supposed to be surviving? How does an agent with no physical manifestation differ from an agent that doesn't exist at all? Swinburne insists that disembodied existence is conceivable and tries to boost the authority of this statement by claiming that "apparent conceivability is evidence of logical possibility". But we can show that this is false. If person X enters a time machine, travels back 2 years then finds, on leaving the machine, it has killed her younger self this sequence of events is apparently conceivable despite containing logical contradiction: How can she have travelled in the machine if she was killed 2 years before entering it? Ideas that can seem coherent when not considered in detail may contain impossibilities and be incoherent on closer inspection. I can dream of doing countless things that, given the physics of the universe, may be impossible in waking reality. Apparent conceivability is NOT evidence of logical possibility. The relationship Swinburne wants to establish simply doesn't exist. And he proves this himself when he admits that if he consists of nothing but matter and the matter is destroyed there is not even a logical possibility that he should continue to exist. This is an admission that it's reality that determines what is possible not our professed ability to conceive of something being possible. If Swinburne says we can survive without any form of physical embodiment that's evidence of nothing more than his opinion. Merely proclaiming he can imagine X doesn't remotely support the factual claim that X is a real phenomenon. If he wants us to take disembodied existence seriously the burden lies with him to provide valid reasons for us to do so. Until its flaws and weaknesses are examined and understood substance dualism can give the superficial impression of addressing some puzzling aspects of minds or consciousness. And many find it appealing because it seems to offer a line of reasoning that allows life after bodily death. However, with the chronic lack, noted by Pat Churchland of any positive description of the nature of the mental substance - or of the interaction between the physical and the non-physical - the content of the hypothesis is specified mainly by saying what the second substance is not making it as inadequate as a theory of light that says only that light is not electromagnetic radiation. With the essentially mysterious (if not incoherent) concept of a 'non-physical thinking thing' at its core dualist explanations, as Max Velmans points out, don't offer genuine alternatives

### Segment 3 (10:00 - 10:00) [10:00]

because they don't tell us how this thing achieves human functioning. All the problems of explaining how such functions operate in the brain simply regress, with added complications. As Velmans says, in the seventeenth century splitting the universe into two fundamentally different substances leaving a non-physical consciousness in the province of theology was liberating for science, enabling investigation of the physical to proceed without interference from the Church. But today things are different. Modern science has reclaimed this subject matter and is making progress with evidence-based insights into the phenomena we classify under the terms 'mind' and 'consciousness' - and this will be the subject of another video.