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.)
I think what Harry's says here is, or at least ought to be, a kind of shorthand for a closely related and much stronger argument.
It isn't just that brain damage can take away your mental abilities. It's that particular kinds of brain damage can take away particular mental abilities, and there's a consistent correlation between the damage to the brain and the damage to the mind.
Suppose I show you a box, and you talk to it and it talks back. You might indeed hypothesize that what's in the box is a radio, and there's a person somewhere else with whom you're communicating. But now suppose that you open up the box and remove one electronic component, and the person "at the other end" still talks to you but can no longer remember the names of any vegetables. Then you remove another component, and now they t-t-talk w-with a t-t-t-terrible st-st-st-stutter and keep pausing oddly in the middle of sentences. Another, and they punctuate all their sentences with pointless outbursts of profanity.
And I have some more of these boxes, and it turns out that they all respond in similar ways to similar kinds of damage.
How much of this does it take before you regard this as very, very powerful evidence that the mind you're talking with is implemented by the electronics in the box?
I endorse this refinement. What brain damage demonstrates is not dependency of talking on the brain, but that the complex computations of thought can be damaged in internal detail by damaging a specific brain part, whereupon its outputs to other parts of thought are damaged. This is strong evidence that the brain is doing the internal computations of thought; it is part of the inner process producing thoughts. The radio hypothesis, in which the output is produced elsewhere and received, decisively fails at that point.
We could suppose that you had a hund... (read more)