He makes an interesting connection between consciousness and the soul after discussing how the two hemispheres of our brains appear to be separate consciousnesses bound together rather than a singular, truly unified consciousness.
"What is most startling about the split-brain phenomenon is that we have every reason to believe that the isolated right hemisphere is independently conscious. It is true that some scientists and philosophers have resisted this conclusion, but none have done so credibly. If complex language were necessary for consciousness, then all nonhuman animals and human infants would be devoid of consciousness in principle. If those whose left hemispheres have been surgically removed are still believed to be conscious--and they are--how could the mere presence of a functioning left hemisphere rob the right one of its subjectivity in the case of a split-brain patient?"
"The consciousness of the right hemisphere is especially difficult to deny whenever a subject possesses linguistic ability on both sides of the brain, because in such cases the divided hemispheres often express different intentions. In a famous example, a young patient was asked what he wanted to be when he grew up: His left brain replied, "A draftsman," while his right brain used letter cards to spell out "racing driver." In fact, the divided hemispheres sometimes seem to address each other directly, in the form of a verbalized, interhemispheric argument."
This he takes to be an argument against the Christian concept of the soul, suggesting that if there is no truly unified physical consciousness which emerges from our brain, then there is no soul in the Christian sense.
"Much of what makes us human is generally accomplished by the right side of the brain. Consequently, we have every reason to believe that the disconnected right hemisphere is independently conscious and that the divided brain harbors two distinct points of view. This fact poses an insurmountable problem for the notion that each of us has a single, indivisible self--much less an immortal soul. The idea of a soul arises from the feeling that our subjectivity has a unity, simplicity, and integrity that must somehow transcend the biochemical wheelworks of the body. But the split-brain phenomenon proves that our subjectivity can quite literally be sliced in two. (This is why Sir John Eccles, a neuroscientist and committed Christian, declared, against all evidence, that the right hemisphere of the divided brain must be unconscious.)"
This seems to be an attempt to kill the soul; admittedly, it is a bold move to attempt to kill something fairly widely believed to be immortal. I have to respect the willingness to make bold arguments, given that I tend to favor bold arguments myself. But is it really so bold? Harris seems to assume that the soul and consciousness are equivalent, at least functionally. And he seems to assume that consciousness emerges from brain activity without any further cause, which is a perfectly valid assumption for someone doing scientific investigation.
If it's true that the soul is equivalent to consciousness and also that it emerges from a physical entity, then on his view the soul cannot be immortal because that which is physical can be destroyed, at least in principle. Perhaps it would be more accurate to say that Harris sets out to kill the mortal soul, given his assumptions about the soul which so pervade his explanation of it. It seems like a strange move for a philosopher to argue against the Christian view of the soul by assuming that its premises are wrong in order to prove them wrong. Isn't that rather like Christians assuming the existence of God as the author of Sacred Scripture in order to prove the existence of God from Sacred Scripture in order to show that atheism is incorrect?
I found myself very confused by this line of reasoning (on both the part of Harris and John Eccles), mostly because I'm not readily familiar with Christian understandings of the soul in which the consciousness, or mind, is identified as the soul. Generally, the soul is understood to be both distinct from and tightly integrated with our body-mind system in an ontological sense. Specifically, the soul is understood as the vital principle from which our bodily and mental faculties emerge.
The understanding of the soul held to by the largest Christian church in the world, specifically the Catholic Church, would seem a useful example. The Roman Catholic Church could be fairly said to have adopted the Thomistic understanding of the soul, and for Thomas Aquinas, there were vegetable, sensitive, and rational faculties of souls, among others. If Aquinas takes the view that only some souls have what we think of as a rational mind, or consciousness, then it seems extremely unlikely that Aquinas was equating the soul with consciousness.
Even if we were to identify consciousness with the sensitive faculty of souls and include other animals, then the fact would still remain that vegetables (in whichever sense one would like to take it) would have souls and yet might easily not have consciousness on the view of Aquinas. There is no way to get to the notion that Aquinas would equate the soul with consciousness. It would seem much more likely that consciousness as we understand it would be a faculty of a certain subset of souls on his view.
Of course, not every Catholic is Roman, and so it might be worth looking at Eastern Christian thought on the soul and its relationship with the conscious mind. On the Eastern Orthodox and Eastern Catholic view, the conscious mind (nous in Greek) is one of several activities or energies of the soul rather than being the soul itself. This too, seems to escape Harris' criticism because it does not equate the soul with consciousness.
There are probably some Christian understandings of the soul as mortal (rather than immortal which is the more common view) that would be compatible with the view that the soul is a consciousness which is an emergent property of our brains. And I'm sure that there are Christians who do believe that the soul is identical to consciousness, and perhaps the point Sam Harris brings forward would be a serious problem for that view. Since I don't agree with that view either, it presents no particular difficulty for me if he does point it out.
It could present a problem for Deepak Chopra, for example, who in this video seems to briefly equate the soul with consciousness. If that brief equation is truly representative of his views, then it might or might not be a problem. If Chopra takes the view that the brain is simply the physical manifestation of the soul-consciousness and that the soul-consciousness is not dependent on the brain for existence, but rather that the brain is dependent upon the soul-consciousness for existence, then it is easy enough for him to suggest that the soul-consciousness has multiple manifestations which are linked together via the brain. And if we damage the brain, he could say that we have merely damaged the physical manifestation of consciousness rather than consciousness itself.
Even in the case of a person who takes the view that the soul is consciousness, there is no particular need for them to commit to the idea that consciousness is solely physical or that it emerges from physical processes. Understandably, Harris seems inclined to think that consciousness is not some sort of spiritual principle and wishes to ground our understanding of consciousness in the physical realm as much as possible, but there is no compelling reason for his intellectual opponents to follow his lead unless they unexpectedly find his desire that they accept his premises a compelling reason.
But this is not the end! Harris has another point against the mortal soul for those who are not convinced of its death thus far.
"In such cases, each hemisphere might well have its own beliefs. Consider what this says about the dogma--widely held under Christianity and Islam--that a person's salvation depends on her believing the right doctrine about God. If a split-brain patient's left hemisphere accepts the divinity of Jesus, but the right doesn't, are we to imagine that she now harbors two immortal souls, one destined for the company of angels and the other for an eternity in hellfire?"
I suppose it's an option that Christians could adjust to the evidence of split-brain patients by claiming that they are granted two souls at the moment of the brain splitting, though I don't see that becoming a popular option.
But just as before, I find myself wondering why that's the proposed outcome. It seems much more likely that those who take the traditional Christian view of the soul would suggest that what matters is what is apprehended by the soul, not what is apprehended by the brain, and that the soul is not dependent on the brain, but rather the brain is dependent on the soul. There's no particular reason for the Christian to assume that if the brain apprehends two things which are mutually exclusive, then the soul must do so as well in some fashion. This is particularly true on the ancient view that the soul has multiple faculties and free will.
The lack of equivalence between the soul and consciousness seems to be yet again a difficulty to overcome in the quest to kill the immortal soul. Far from killing the Christian concept of an immortal soul, Harris seems to have at best killed the concept of a mortal soul, a soul which is merely a unified consciousness, perhaps an emergent property of physical processes. I completely agree that such a mortal soul does not make much sense in light of the evidence, so to that I say, "Good work, sir!"
Now that the mortal soul has been killed, perhaps we can turn our attention to the immortal soul. To rephrase a traditional proclamation: The soul is dead. Long live the soul!
Note: Photo credit goes to me.