No plot spoilers here, just wanted to flag a bit of poor reasoning that shows up in Chapter 39:
I shouldn't have believed it even for all of thirty seconds! Because if people had souls there wouldn't be any such thing as brain damage, if your soul could go on speaking after your whole brain was gone, how could damage to the left cerebral hemisphere take away your ability to talk?
This is a surprisingly common fallacy. Just because X depends on Y, it doesn't follow that X depends on nothing but Y. A phenomenon may involve more than just its most obvious failure point.
To illustrate: Suppose I'm trapped in a box, and my only way to communicate with the outside world is via radio communication. Someone on the other end argues that I don't really exist -- "There's no person beyond the radio receiver, for if there was then there wouldn't be any such thing as damaged radios!" Pretty silly, huh? But people say this kind of thing in defense of physicalism all the time.
(N.B. This is not to defend the existence of souls. It's just to point out that this particular argument against them is invalid.)
Thanks, that's helpful. Two (related) possible replies for the afterlife believer:
(1) The Y-component is replaceable: brains play the Y role while we're alive, but we get some kind of replacement device in the afterlife (which qualifies as "us", rather than a "replica of us", due to persisting soul identity).
(2) The brain is only needed for physical expressions of mentality ("talking", etc.), and we revert to purely non-physical mental functioning in the afterlife.
These are silly views, of course, but I'm not yet convinced that the existence of brain damage makes them any more so than they were to begin with. (They seem pretty natural developments of the substance dualist view, rather than big bullets they have to bite.)
Are you agreeing, then, that X=mind and Y=brain chunks? That's surprising to me. I would have thought that X was all of the relevant behaviors -- walking, talking, breathing, playing games, writing on internet forums, ... I didn't think you would want an identity thesis between Mind and Some Class of Behaviors. Maybe I'm thinking about this wrong, but I thought for soul-ish theories, the mind just was the soul. And then you get a causal picture (for interactionists, anyway) that looks like Soul --> Brain --> Intelligent Behaviors.