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 hundred soul-parts, all of which can only communicate with each other through brain-area radio transceivers which receive a call from one soul-part, and then retransmit it to another. But leaving out the epicycleness of this idea, the degree to which it contradicts the intuitive notion of a soul, and its, if you'll pardon the phrase, sheer stupidity, the end result would still be that destroying the brain leaves the soul incapable of thought. You're not likely to find a remotely reasonable hypothesis, even in the Methodsverse where magic abounds, by which the internal parts of a thinking computation can be damaged by damaging the brain, and yet removing the whole brain leaves the soul capable of internal thinking.
I kind of liked one of the HPMOR recursive fanfics which played with this since in the Methodsverse wizards continued to be able to think even when their brain was replaced with that of a cat.
If I remember right in that fic the blood-purists maintained that only wizards had souls and that the thing they used to prove it was by feeding polyjuice to a non-wizard who would lose their own personality in favor of the body they were copying for the duration of the potions effects. (not having a magical soul with which to maintain their thought patterns when their physical brain was changed)
You're not likely to find a remotely reasonable hypothesis, even in the Methodsverse where magic abounds, by which the internal parts of a thinking computation can be damaged by damaging the brain, and yet removing the whole brain leaves the soul capable of internal thinking.
Has your hypothesis that thought remains possible after the whole brain has been removed, in fact, been tested?
EDIT: I read your post as meaning that the "fact" that thought remains possible after a brain has been removed [to be cryo-frozen, for instance] was evidence against a soul.
You're not likely to find a remotely reasonable hypothesis, even in the Methodsverse where magic abounds, by which the internal parts of a thinking computation can be damaged by damaging the brain, and yet removing the whole brain leaves the soul capable of internal thinking.
Why not? Letting a brain decompose kills the "thinking computation", while cryonizing it supposedly does not.
Similarly, damaging a living brain may damage the attached soul, while death of a reasonably intact brain could be interpreted as a detachment of a reasonably intact soul.
Are you supposing that oxygenating a human's blood without the use of lungs would result in the loss of their soul?
I think you will find that the only way to exclude such hypothetical possibilities is to define death as sufficient brain damage (although I suppose you could define it as cessation of neural activity if you don't mind the possibility of dead people coming back to life; that would still result in a very large proportion of souls being damaged)
Are you supposing that oxygenating a human's blood without the use of lungs would result in the loss of their soul?
Sure, but they'll get it back (and lose 30 IQ points and a whole bunch of cool) if cursed by gypsies.
We are not talking about anything real-world, remember. The original setting:
a remotely reasonable hypothesis, even in the Methodsverse where magic abounds
This also applies to my piano analogy. Remove the middle C string, and you'll hear silence wherever there's supposed to be a middle C. Remove the dampers, and the piano will sound like the sustain pedal is constantly held down. Tune each G# string a semitone higher, and you'll hear an A wherever a G# is supposed to be.
That doesn't seem at all similar. The brain is, in this analogy, more like an instrument where if you remove one string it still works for most things but will no longer let you play anything by Mozart, and if you remove another everything comes out syncopated, and if you remove another then you can still play everything but all rubato disappears so that rhythms become metronomic. See also my reply to billswift.
It's not valid as a deductive argument, but it is Bayesian evidence in favour of naturalism. Also, the details of the observed effects of brain damage provide even more for naturalism rather than nonnaturalism.
It's not valid as a deductive argument, but it is Bayesian evidence in favour ...
You can say that about pretty much anything labeled a "fallacy".
For example, the "appeal to authority fallacy" --> yes, an authority on the matter is not guaranteed to be right, but their opinion is Bayesian evidence in favor of such beliefs.
Fortunately, a poster already wrote an article with that thesis.
I disagree that Kaj_Sotala's post applies. Just because you label something a fallacy doesn't make it a fallacy. Googling the "radio fallacy" turns up this thread and nothing else related.
This 'radio fallacy argument' wants to place Harry's argument into the reference class of 'fallacies' and has nothing but a clever label and bad analogy as that basis.
It's not valid as a deductive argument, but it is Bayesian evidence
The "not a logical disproof" defense can be used against more or less all arguments drawing on empirical science. It would be more charitable to assume Richard means something like "the probability of brain damage by region delicately affecting particular parts of information processing is reasonably high given belief in souls." Although that still looks quite wrong. The "radio" analogy would not predict a speech center, or other patterns of brain damage and impairment that look like interfering with computation, not transmission.
That's surely going to depend on the details of the non-naturalist view. Epiphenomenalism, for example, makes all the same empirical predictions as physicalism. (Though it might be harder to combine with a "soul" view -- it goes more naturally with property dualism than substance dualism.)
But even Cartesian Interactionists, who see the brain as an "intermediary" between soul and body, should presumably expect brain damage to cause the body to be less responsive to the soul (just as in the radio analogy).
Or are you thinking of "non-naturalism" more broadly yet, to include views on which the brain has nothing whatsoever to do with the mind or its physical expression? I guess if one had not yet observed the world at all, this evidence would slightly lower one's credence in non-naturalism by ruling out this most extreme hypothesis. But I take it that the more interesting question is whether this is any kind of evidence against particular non-naturalist views that people actually hold, like Cartesian Interactionism or Epiphenomenalism. (And if you think it is, I hope you'll say a bit more to me to explain why...)
Let's walk through this slowly.
Harry notes that we can see that mind function depends on brain function. Take a chunk out of a brain, the mind associated with it doesn't work so well. Harry notes the insanity of thinking that taking away all the brain chunks leaves you with a working mind.
You object
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.
X = Mind. Y = Brain Chunks. Let X depend on Brain Chunks and Soul and Astral Flubber. If your mind is dependent on all of them for proper operation, then you can't speak when all your brain chunks are gone. End of story. You can play epiphenomenal games and argue that "yes, but you still have Soul and Astral Flubber." But who cares? All mind function is lost. I may "have" eternal and indestructible Astral Flubber, but what good does it do me?
Harry is clearly arguing against continued function after physical destruction, not against "having" a big pile of epiphenomenal astral hand bags, full of epiphenomenal astral stuff. He was hoping for functional minds after death, and noted how foolish that was.
No logical fallacy involved. Nothing to see here, move along.
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.)
Did these fundamentally arbitrary assertions get more stupid? That's an angel dancing on the head of a pin argument.
Notice that those weren't the assertions before we learned about brains. The mind was a spirit/soul mysteriously trapped in a physical body. Then we started poking around in brains, and finding that the mind didn't seem to work so well when bad things happened to the brain. So minds retreat to epiphenomenalism. Then they can retreat in time, and only actually do anything after you're no longer alive, and no one can see anything actually happening.
So, yes, the original theory of the soul got less likely after we learned about brains, but your new theory of the soul, specifically crafted to avoid contradiction with the new evidence, might not have.
God, souls, immaterial minds, elan vital, essences, etc., are all a bunch of cockroaches, always scurrying back into the darkness, retreating from the expanding light of evidence. How many retreats do we need to see before we're convinced they will never be able to stand their ground?
I anticipated the "functional swap at death" argument, as it was the logical next rampart to retreat behind, but thought it was pointless to say anything about it. I think we've learned by now that the chase never ends. I could just as well say that your mind will continue only if you had duck within a week of your death, and the Spirit of the Duck was within you to transfer the function of your mind to live out the rest of eternity in a lamp post. That's a spiritual lamp post, of course. We can't actually see the the lamp post, you silly goose. Or should I say, silly duck?
We really need a clear and concise statement for the rejection of the infinite class of arbitrary assertions consistent with all currently known data.
Notice that those weren't the assertions before we learned about brains.
The first was an assertion before we knew more about brains. Richard Carrier in particular believes that this is pretty much what Paul and early Christians believed 1,2; that you need to be given a new body in the resurrection in order to have life after your normal body is destroyed. According to Carrier and others it wasn't an uncommon belief that humans gained another better body spiritual body at the resurrection. Spiritual body in this case doesn't mean non-physical, but instead is to be interpreted as the element which the heavenly bodies are made from.
If you are interested in reading more about it, I have other books to recommend on the subject. I do agree with you however that these possible replies are stupid.
There are different variations. The Jehovah's Witnesses don't believe in immaterial souls separate from the body. All life occurs as a material body. They get rid of hell too. Rather sensible, I think.
I couldn't quite tell from your comments whether you're referring to people with similar beliefs to the Witnesses, or people who say you have a soul, but it (waits around? exists but has no sensation?) until God gives it a shiny new body.
I assume there are all conceivable permutations of when/where/how/if souls exist, and I don't have a stand on whether the first Christians believed in immaterial souls or not. Maybe some did, some didn't? Truth be told, I was thinking about a thousand years back, by which time I believe an immaterial soul was taken as given through most of Christendom. Mind body dualism seems to go a long ways back with animism, ghosts, and spirits. What do you have to say about the general history of materialism versus dualism?
It is similar to the Witnesses as far as your description goes, though I am not very familiar with JW's beliefs to comment further on the similarities.
My only point was that this is an old idea (that you need a body to function and that you get given a new body of some wondrous sort upon death), and not one contrived as an escape from the physicalists death blow. The debate is over and done for me, and I as you see the moves of the dualist as always failing to substantiate the additional substance.
(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.
It seems the considerations in gjm's comment actively tear (2) to shreds.
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.
X = Mind. Y = Brain Chunks. Let X depend on Brain Chunks and Soul and Astral Flubber. If your mind is dependent on all of them for proper operation, then you can't speak when all your brain chunks are gone. End of story. You can play epiphenomenal games and argue that "yes, but you still have Soul and Astral Flubber." But who cares? All mind function is lost. I may "have" eternal and indestructible Astral Flubber, but what good does it do me?
This only follows if the impact from the Soul and Astral Flubber.is negligible. You could see a situation where it wasn't purely epiphenomenal and where tests could be made to verify that. For example, one could make an extremely detailed emulation of the brain, and if it then became apparent that that was failing at a variety of different levels, that would be evidence for Astral Flubber or the Soul having a direct impact on the wetspace version.
First, just the obvious "my simulation doesn't work" does not imply Soul or Astral Flubber exists or that it does something. The more reasonable interpretation is that your simulation sucks.
This only follows if the impact from the Soul and Astral Flubber.negligible.
No, it doesn't. Both could have great impact when combined with a brain, but take away the brain, and you have no function. Harry wanted the continued function of the mind after physical destruction of the body. Even if the mind dependency is Brain AND Astral Flubber, brain gone means mind gone. Astral Flubber has not shown the capability to replace the function of brain chunks, so why would we expect it to replace the function of all the chunks together?
First, just the obvious "my simulation doesn't work" does not imply Soul or Astral Flubber exists or that it does something. The more reasonable interpretation is that your simulation sucks.
For the initial simulations yes. If for example humans spent fifty years making more and more detailed simulations and they still didn't work, and there was no sign that they were improving at all, the existence of some really weird new physics shouldn't be discounted at that point.
No, it doesn't. Both could have great impact when combined with a brain, but take away the brain, and you have no function. Harry wanted the continued function of the mind after physical destruction of the body. Even if the mind dependency is Brain AND Astral Flubber, brain gone means mind gone.
This seems like a much stronger point. The evidence shows that Astral Flubber is at least not sufficient, and the brain is really doing almost everything that matters.
Suppose you damage the "radio", and suddenly the voice on the other side starts murdering people. This is starting to look like more than just bad reception, isn't it?
I'd agree that "ability to talk" is a much weaker example of the same general argument, though.
Several people in this thread offer the argument that since damage to specific brain regions causes function-specific deficits in behaviors (e.g. damaging Broca's area causes Broca's aphasia -- the loss of ability to produce grammatically correct sentences), dualism -- or at least interactionist dualism -- must be false. Just to play devil's advocate -- it seems to me that the argument depends a lot on the details of "soul-theory." For example, if your picture is roughly Cartesian interactionism, the argument isn't persuasive. (Though a related argument might be.) Recall that Descartes said something like, "The soul wiggles the pineal gland, which wiggles the brain, which wiggles the body." Descartes could have said that damaging something like Broca's area prevented the soul from producing grammatical sentences because the pineal gland couldn't wiggle the right mechanisms anymore.
The causal picture for Descartes (or any one-point-of-contact interactionist) would be something like Soul --> Pineal Gland (or whatever the point of contact is) --> Broca's Area (or whatever the relevant brain area is) --> Grammatical Language Production (or whatever the function of the relevant brain area is).
The one-point-of-contact interactionist should predict that there will be a single brain region such that lesioning it will shut down all intelligent behavior. And so it is vulnerable to empirical criticism.
Alternatively, one might be a multiple-point-of-contact interactionist. One might suppose that the soul is as complex as the brain itself, and one might suppose that each soul-component interacts directly with a specific brain region. Anyway, you can see how this might go.
As I see it, the likelihood of the evidence being considered here (local brain damage causes specific behavioral deficits) on either of these theories is as high as it is on physicalism.
(As with Richard, I am not trying to defend the existence of souls. I think dualism is false. But the argument on offer is not a very good one.)
I can't think of better arguments agains souls than the one on offer. It is among the most observation-based arguments we have and observation-based arguments are usually much stronger than a priori reasoning.
Soul --> Pineal Gland --> Broca's Area --> Grammatical Language Production
The problem with this (and related theories) is that the soul believers believe that the soul itself can live and think without the body. Much of thinking is mediated by language. I don't think a believer in soul would accept that their soul after death will be incapable of thought until God provides it a substitute pineal gland.
As I see it, the likelihood of the evidence being considered here (local brain damage causes specific behavioral deficits) on either of these theories is as high as it is on physicalism.
Yes, enough complicated theories postulating brain-dependent souls can survive the argument without harm. But these theories are standing pretty low a priori - as I have said above, ordinary believers believe in a brain independent soul, rather than in complex non-beliefs specifically constructed to make existence of soul untestable.
It is among the most observation-based arguments we have and observation-based arguments are usually much stronger than a priori reasoning.
Well, yes, except that the observations being called on here don't actually differentiate between soul theories and non-soul theories. That was the whole point of my remark: both kinds of theory save the phenomena.
The problem with this (and related theories) is that the soul believers believe that the soul itself can live and think without the body. Much of thinking is mediated by language. I don't think a believer in soul would accept that their soul after death will be incapable of thought until God provides it a substitute pineal gland.
This just looks like a non sequitur to me. If the soul thinks on its own but only gets to communicate to other souls via a body, you get the same observational consequences. If souls have their own language of thought, then thinking might still be mediated by language and yet that mediation not require a body. (On a side note, medieval theologian-philosophers had a very serious argument about whether dis-embodied souls could sense anything. I don't think it's a huge stretch from "a soul requires a body in order to have sensations" to "a soul requires a body in order to think anything." One question you might want to ask here is whether you are interested in going after the best possible soul theory or going after the probably-confused beliefs of typical soul-believers.)
I agree with your last remark -- that soul theories are less probable a priori. But that wasn't the issue that Richard was raising. The question is how the evidence of specific functional losses due to specific, localized brain damage bears on soul theories (or dualism more generally). Evidence only comes in through the likelihood. Simplicity arguments are, I think, good arguments against souls: souls get shaved right off by Ockham's razor. But simplicity arguments are not arguments from evidence, they are arguments from method. That is, the evidence could be equally likely on two different hypotheses but one of them could still be preferred -- not because it fails to save the phenomena but because it requires extra machinery in order to do so.
If the soul thinks on its own but only gets to communicate to other souls via a body, you get the same observational consequences. If souls have their own language of thought, then thinking might still be mediated by language and yet that mediation not require a body.
I haven't said "thinking is mediated by language, therefore souls need body to think". I have said "if souls need body to understand and actively use language, then souls need body to think".
One question you might want to ask here is whether you are interested in going after the best possible soul theory or going after the probably-confused beliefs of typical soul-believers.
To answer your question reliably I'd need to know what do you mean by "the best possible soul theory". If it means "the theory which is most carefully crafted to avoid contradiction with observational evidence", then I am probably more interested in beliefs of typical soul-believers. Moreover, I wouldn't call the overfitted soul theory "best" and the ordinary beliefs "confused"; this creates impression that theology clears up confusion of folk religion. My opinion is that theology only replaces simple confusion with elaborate confusion of greater magnitude.
I wonder whether anybody would start believing in soul if the idea was first presented to them in form of "the best soul theory".
What I mean is just to give your opponent the best possible position reasonably consistent with his or her assertions. In other words, be charitable. The reason is that if you knock down a weak version of your opponent's thesis, you leave the stronger versions on the table. Why not knock them all down by taking on the strongest possible version of your opponent's thesis?
Moreover, I wouldn't call the overfitted soul theory "best" and the ordinary beliefs "confused"; this creates impression that theology clears up confusion of folk religion. My opinion is that theology only replaces simple confusion with elaborate confusion of greater magnitude.
Those are not incompatible. A soul theory could be the best of its kind and still be a worthless pile of confusion. My point, again, is just to give the opponent the best shot possible at being right (without, of course, just making him or her a physicalist).
I don't think it's a huge stretch from "a soul requires a body in order to have sensations" to "a soul requires a body in order to think anything."
There are certainly theologians who have posited that souls do not do anything so crass as 'thinking', but I can't think of a reference at the moment.
The problem with this (and related theories) is that the soul believers believe that the soul itself can live and think without the body. Much of thinking is mediated by language. I don't think a believer in soul would accept that their soul after death will be incapable of thought until God provides it a substitute pineal gland.
Actually, the concept of soul without language makes more sense on its own and fits more religious traditions (especially if you abandon literal translations) than souls that have language.
(shrug) Sure. It's not a logical impossibility that all the valuable stuff resides in the soul, and that the brain serves only relatively valueless functions (akin to a radio), such that when we eliminate the brain the bulk of the value is preserved.
One question worth asking is how much attention I want to pay to "is X logically impossible?" vs "does there exist enough evidence for X to make it worth considering?"
Or, in the context you raise this in, "should we understand Harry to be talking about whether the soul hypothesis is logically possible, or talking about whether the soul hypothesis is worth considering?"
The utterance you quote is consistent with both readings.
I agree that the soul hypothesis is not generally worth taking seriously. What I'm denying is that the existence of brain damage is good evidence for this.
Well... the existence of brain damage, in and of itself, is not evidence for this, I agree.
That is, if I lived in a world where (for example) brain damage existed but cognitive impairment didn't follow from it, in much the same sense that skeletal damage does not result in cognitive impairment in the actual world, the mere existence of brain damage would not tell us much that's relevant to the soul hypothesis one way or the other. (And, relatedly, in the real world I don't think the existence of skeletal damage is good evidence for or against the soul hypothesis.)
But I would also say that the facts that normal cognitive function reliably occurs in the presence of normal brain function and fails to occur in the absence of normal brain function, and that brain damage reliably predicts variations in cognitive function, and that there's no evidence that variations in the soul predict variations in cognitive function, constitute good evidence that souls are not causal to cognitive function.
If I've understood you correctly (which is by no means guaranteed) we disagree here.
I had thought of a very similar example about why that particular argument is invalid: removing or de-tuning some of the strings of a piano will affect its sound, but it doesn't follow that the strings are all that's needed to explain the music from the piano with no need for there to be a pianist who hits the keys.
I have a feeling that if Harry was to say this to Draco, he would reply: your studies were all carried out on Muggles, and everyone knows Muggles have no souls!
The radio analogy is bad because of the first person point of view.
The radio == the external behavior of the person, and you == the soul, right?
Damaging the brain doesn't just affect the external behavior of the person, it also affects the person's thinking, i.e. the person itself. Therefore, the brain isn't just a receptor for a signal, as the radio is, it's the thing doing the thinking.
That's certainly true, but I'm not sure it matters.
One could replace the radio receiver/transmitter analogy with an algorithm-specification/algorithm-implementation analogy, for example, without significantly affecting the argument. Is the hardware the thing doing the thinking? Well, yes, in that when we destroy the hardware we prevent the thinking. But, no, in that even after we destroy the hardware we can recover the thinking by implementing the algorithm on other hardware.
Generally speaking, I think it's better to address the argument being implied by a metaphor than to address weaknesses of the metaphor itself. See also "steel-manning."
That's a completely different concept of 'soul', one that I doubt anyone who says, "I believe in the existence of souls" actually has in mind. People who believe in souls believe they are their soul, not that they are their brain and that their brain implements soul-code.
It's generally a good idea to try to understand what people actually believe, rather than what you think they should believe.
I agree with you that most people who believe in souls identify with their souls rather than their brains, and it's not clear to me how any of what I said changes depending on whether people identify with their souls or their brains. But I'm also not strongly committed to this particular metaphor; if you have one you prefer, or have a different formulation of the argument in question you'd prefer to use that doesn't depend on metaphor at all, I'm happy to use that as well.
It is certainly a good idea, but it is not always easy to determine what people believe. On the present topic, they believe quite a variety of things, many of them extremely unclear. Why do you assume that if brains implemented soul-code as you describe, someone would think it was the brain that was them, rather than the soul-code? The view that brains implement soul-code and that the soul-code is the real person sounds to me like a not implausible interpretation of much of what Plato says about souls.
Just a couple points about the radio analogy:
If the brain is a radio, wouldn't it need to transmit as well as receive? Otherwise the soul wouldn't know what's going on. It would be nice to detect that transmission...
We know the brain undergoes change as memories are formed, etc. If the brain is a radio, why does it need to do that?
A damaged radio should not be capable of removing all descriptions of "left" from your transmission. Harry's problem is that the effect of damage allows inference about the nature of the generating algorithm that strongly excludes some external source.
I don't believe cars actually function via mechanical forces. It is the car's machine spirit which moves the vehicle.
If my car's timing belt gets broken or the alternator is malfunctioning, that doesn't stop the car. Clearly the machine spirit is strong enough to move the car even without a timing belt. However, the car's machine spirit will become angry and run sporadically, or lethargic at my poor maintenance and unwilling to start. The machine's spirit shall not be appeased until I take it to a proper mechanic so that he may assuage it with the holy rites and coax it to run again.
Those heretics who do not believe that cars have souls are simply making the Radio Fallacy. Fortunately I have seen the truth. Praise the Omnissiah!
I don't understand. Did you read the rest of what I wrote, where I gave some specific examples of the kind of damage we're talking about? (Note: they weren't intended to be neurologically perfectly accurate.) Do you not agree that if you had a device that produced such effects when damaged, it would be grossly unreasonable to think it was a radio rather than an AI?
[EDITED to add: Of course I agree that there are situations, quite different from what we see in the real world, that could also -- just barely -- be described by saying "particular kinds of damage to the brain produce particular kinds of apparent damage to the mind", but where that would not be very strong evidence that the mind is implemented by the brain. For instance, you damage one bit of the brain and the person's voice goes squeaky; you damage another and all the consonants go away. What's different about the real world is that particular kinds of brain damage have particular semantic signatures; they are bound up with the content of what's being thought or said.
It's still consistent with all this that the mind isn't implemented only by the brain. If every aspect of human thought required cooperation between the brain and the soul, you could still get the sort of thing we actually observe. But let's distinguish between "there are some theories of souls that are consistent, at least in principle, with these observations" and "these observations do not constitute a good reason not to believe in souls". The former is probably true, the latter not.]
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.)