Can numerically distinct individuals be mentally qualitatively identical? That is, can distinct entities share all of their mental properties? I think the answer to both questions is “yes”. This invites the further question of how such a situation is even conceivable and here the physicalist is in much better shape than the dualist.
The physicalist can say that numerically distinct individuals sharing all of their mental properties acheive numerical distinction in virtue of their physical properties. A dualist cannot. This raises the serious problem of how the individuals in question can be distinct at all.
To get a clearer sense of the problem, let’s begin with the substance dualist. Is it conceivable that there is a world with nothing other than two distinct Cartesian egos - distinct non-spatial conscious entitites - that have all and only the same thoughts and experiences? It seems not. What could possibly serve to distinguish them?
The dualist might reply here that the physicalist is in no better shape since similar problems can be raised with purely physical objects. Is it conceivable that there is a world with nothing other than two numerically distinct yet qualitatively identical steel balls rotating around each other? If so, what makes them conceivable? Here the physicalist may say that we conceive of their distinctness by imposing a coordinate system on the scene that places one of the balls at the origin. Of course, this effectively introduces qualitative differences and may be cheating. But at least the physicalist knows how to do this. We know what it means to impose a coordinate system on spaceballs. We have absolutely no idea what it would mean to impose a coordinate system on Cartesian egos.
At this point the property dualist may be feeling that the problem posed applies only to substance dualists. The property dualist may think they can help themselves to physical differences between individuals in a way that the substance dualist cannot. What distinguishes numerically distinct yet mentally identical individuals? The property dualist may think that they can answer “physical properties” as easily as the physicalist. However, this is not so. Consider the question of a world in which there are two distinct minds but only one body (with only one brain). If mental properties are indeed distinct from physical properties, then the dualist would have no grounds for ruling out the absurd situation of multiple numerically distinct yet qualitatively identical minds inhabiting the same body/brain. And if the property dualist thinks they can help themselves to supervenience at this point, then they face the problem of regress discussed previously here.
Fig. 1: Numerically distinct individuals comparing that with respect to which they are qualitatively distinct.
You said:
Consider the question of a world in which there are two distinct minds but only one body (with only one brain). If mental properties are indeed distinct from physical properties, then the [property] dualist would have no grounds for ruling out the absurd situation of multiple numerically distinct yet qualitatively identical minds inhabiting the same body/brain.
I don’t see this. The reasonable property dualist probably believes that anything with mental properties also has physical properties, but not necessarily vice versa. This would rule out two minds, one object universes.
This is orthogonal to supervenience, though they would get supervenience by saying adding that if an object has mental properties, any type-identical physical object has the same mental properties. This would be nonnaturalist, of course, so they shouldn’t mind your argument that you must either be an identity theorist or a nonnaturalist.
Eric, you are right that the reasonable dualist would probably believe that, but another way of putting my point that the “dualist would have no grounds for ruling out the absurd situation” is to point out that the dualist has no reason or principled basis for ruling out that situation. My point, then, is that without some reason for ruling out that situation, simply saying that it won’t occur looks like an ad hoc stipulation. My point is that dualism seems to entail that this thing is possible. If the thing in question is absurd, then this entailment is a bad thing for dualism.
I think they would use the same reasons that other people have for straight-out physicalism. That is, empirically there is no evidence that minds occur in the absence of physical properties. But, since they agree with Chalmers-esque arguments, and can’t see how identity theory can explain qualia, they need to add extra properties to the universe.
On the days when I buy the Chalmers line, I think something like this is the only reasonable alternative to naturalism.
While physicalists may be impressed with what does and doesn’t happen empirically, Chalmers-esque arguments for property dualism go beyong the empirical and involve appeals to what allegedly goes on in logically possible non-actual worlds (like worlds populated with our zombie twins). If qualia are the sort of things that can be cut free of the physical that radically, then I don’t see how they can rule out the multi-mind scenario. And if they do manage to rule it out on the grounds of something like supervenience, then they’re going to be vulnerable to the regress argument we’ve previously discussed.
I have the strong intuition that two qualitatively indiscernible immaterial minds would nonetheless be thinking different things when they thought “I’m happy!” Would this be sufficient to distinguish them? Or does my intuition seem wrong to you?
Hi Geoff,
Thanks for the comment. I’m having a hard time, though, seeing how to describe your intuition in a way that doesn’t make it seem contradictory. These immaterial minds, I suppose, have only mental properties. If they are indeed indiscernable with respect to the mental, then what ever they think, it must therefore be the same thing. If they think different things, then they wouldn’t be indiscernable with respect to the mental.
Perhaps, then, I’m missing something about your intuition. It occurs to me that perhaps you meant something other by “qualitatively” than I initially supposed. What I intended in the inital post was for qualitative identity/non-identity to cover the sharing/not sharing of any properties. But perhaps you intend something like qualitaitve in the sense of pertaining to qualia? If so, then your intuition may very well be non-contradictory: two minds may have all the same qualia yet diverge in what it is they are thinking. However, this later situtation wouldn’t really constitute a counter-example to the claims I’m trying to make.
Cheers,
Pete
Thanks Pete; fair enough. Second try:
By “qualitative properties” I was thinking something like: properties it’s logically possible for numerically distinct objects to share. If you don’t have this restriction the answer to your question is obviously and trivially “no, such a pair of minds is not conceivable, nor is any other ‘pair’ of objects of any substance whatsoever”. E.g., object A has the property of being identical with A, and it’s obviously inconceivable for a numerically distinct object to share this property with A. You’ll get the same trivialization of the question if you include any such properties among those we stipulate to be the properties wrt which the objects are indiscernible.
So here’s another try at the intuition:
Each mind thinks to itself “I’m happy” and thereby thinks about itself. So A is thinking about A by thinking “I’m happy”, and B is thinking about B by thinking “I’m happy”. They have the same thought, but each thought is about a different thing. And this is sufficient to conceive of them as distinct.
Now you might say that thinking about A by thinking “I’m happy” is a mental property, and hence one that we have stipulated that both minds share. But it’s not logically possible for numerically distinct entities to share that property. So you shouldn’t include it among the set of properties we stipulate that the minds-to-be-conceived share.
Thanks, Geoff. That is quite helpful. I see now that the inuition offered is not contradictory. I still have some reservations, though, preventing me from sharing with you the judgment that the imagined scenario is strongly intuitive. The brief version of what’s bothering me is that when I try to get a handle on what it is in virtue of which that a and b are supposed to be conceivably distinct, I wind up with a tight little circle. Consider:
In virtue of what are a and b distinct? In virtue of their distinct first-personal thoughts. In virtue of what are their first-personal thoughts distinct? In virtue of being about distinct entities, namely a and b. And now we must go back to where we started: In virtue of what are a and b distinct?
If a and b each had first-personal thoughts of distinct entities, then those thoughts would suffice to distinguish a and b. However, we have no way of knowing whether they have first-personal thoughts of distinct entities unless we already know whether a and b are distinct. Compare and contrast this situation with the following.
If we knew that Mark was thinking of Hesp and not Phosph and Sam was thinking of Posph and not Hesp, then that would suffice to distinguish Mark and Sam regardless of whether we knew if Hesp and Phosp are distinct.
However, if all I knew of Mark was that he was thinking first-personally of himself and all I knew of Sam was that he was thinking first-personally of himself I would be in no position to decide whether Mark was Sam.
Thanks for your reply, Pete. I thought the task was to explain how qualitatively identical minds are conceivable as distinct, not to say what it is in virtue of which such minds would be distinct. That A’s first-personal thoughts are about A and B’s are about B seems enough to me to conceive of A and B as distinct, and it’s not a qualitative difference between them. (Note that I don’t say, as you do of Mark and Sam, that A and B each thinks first-personally of himself; that’s a qualitative similarity and hence insufficient to enable us to conceive of them as distinct.) But of course this doesn’t explain what makes it the case that A and B are distinct. So if that’s what you are after, I’m happy to concede that I don’t have an answer.
As to that deeper question, though, I’m inclined to say that there needn’t be an explanation for distinctness, because identity and distinctness are primitive. You seem otherwise inclined, so I certainly see why you find my intuition uncompelling.
But just to push a bit on the idea that distinctness requires an explanation: suppose there were another universe spatio-temporally disconnected from ours, but which is an exact physical duplicate of it. This seems to me to be perfectly conceivable. If you agree (and I don’t know what non-dogmatic reason you’d have for disagreeing), then what is it in virtue of which our universe and its double would be distinct? The only answer I can see is: nothing. They just would be.
Geoff, thanks for pursuing the issue this far. It’s been illuminating and I think you’ve correctly identified the sorts of considerations this would all come down to. I haven’t completely made up my mind about whether I think numerical identity is primitive, but I’m guessing that it would take relatively elaborate theoretical considerations to convince me that it is. Simply considering, for example, the two universes case leads me to simply say - dogmatically, I suppose - that they don’t strike me as conceivably distinct. And when I suspend my dogma, I don’t know how to proceed.
I find interesting your suggestion that we separate the questions of explaining the distinctness of a and b and the question of how we may conceive of them as distinct. I must admit that I hadn’t previously been separating the two. I think I can go along with this for the sake of argument, though. Suppose then, that there are two distinct individuals for which there is no explanation of how they are distinct. What, then, would count as an answer to the question of how it is that we conceive of them as distinct? Is the answer “we simply do”? Is the person who takes identity to be metaphysically primitive also forced to take it as epistemically primitive? If the answers to the latter two questions are “yes”, then that strikes me as kind of unsatisfactory, insofar as it turns out there is no answer to the question that immediately preceded them. However, I guess this wouldn’t be the worst thing in the world: there are worse suggestions for what to regard as epistemically primitive.
Pete, I heard Jaegwon Kim raise an argument very similar to this one at a talk in 2000 or 2001, in case you’re interested. The idea was, if I remember right, that space provides a way of individuating indiscernibles, but that this isn’t how ‘Cartesian souls’ could be individuated. I can’t remember the paper, but some of this line of argument may have made it into “Lonely Souls”.
Nick, I wasn’t aware that Kim may have scooped me on this. Thanks for the tip!
Sorry I can’t remember the details more clearly, Pete. I know Jaegwon’s argument was very similar to yours, even in regard to appealing to the notion of a coordinate system. You can just think of it as “great minds think alike”. (Although hopefully not _too_ alike, for the reason that you/he suggest!)
I haven’t yet tracked down Kim’s paper, but I did snoop around the internet a bit for summaries of the argument. The impression I got was that Kim’s issue concerned certain problems of mental-physical interaction that arise for Cartesians. My argument isn’t specifically about causation. Also, I wonder if Kim mentions extending these points to property dualism as I do.
Well, I guess I better read that article! Thanks again, Nick.
I thought Kim had two arguments that are along these lines:
A first argument is roughly that because Cartesian souls are outside spacetime, there’s no way to pair mental causes with physical effects. Suppose two guns go off, and one bullet hits Smith, who drops dead. We can understand Gun A being the cause of the death and not Gun B because Gun A and Gun B are located differently in space.
The second argument, I thought, was very much like the argument you mentioned, that we could not make sense of two mentally indiscernible Cartesian souls.
Of course, I could be misremembering…or perhaps I misinterpreted Kim at the time as giving the second argument. It was five years ago or so. Probably a quick email to him would sort it out.
I don’t remember the argument discussing property dualism at all, by the way.
If you end up writing this argument up into a paper, I’d love to have a look at it.
cheers.
Most dualists I’m aware of deny relativity and believe there is a priviledged space-time. While this seems implausible on the face of it they appeal to the problem of reconciling QM to relativity and suggest a lorentzean reading of relativity as opposed to an Einsteinian reading is appropriate. Needless to say as a physicist I don’t find this persuasive in the least. However apparently John Bell said something similar. There are a few papers on this in the context of debates over presentism at the philosophy of science repository. Obviously they don’t discuss dualism but I think they are relevant to Kim’s argument.