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.

Well, I guess I better read that article! Thanks again, Nick.

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.

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.

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.

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.