The modal arguments for substance dualism in the philosophy of mind require a possibility premise, for example, 'It is possible that a person exist disembodied,' or 'Possibly, a person becomes disembodied.' One question concerns the support for such a premise. Does conceivability entail possibility? Does imaginability entail possibility? And if neither entail possibility, do they provide sufficient evidence for it? I'm not done with these questions, but there is another vexing question that I want to add to the mix. This concerns the validity of the inference from
to
2. Some actual person can exist disembodied.
(1) is de dicto: it says of a dictum or proposition that it is possibly true. (2) is de re: it says of a res or thing that disembodiment is one of its possibilities. To see the difference, consider that (1) can be true even if every actual person is a purely material being, and thus a being for whom disembodied existence is not a possibility. On that supposition, (2) is false. So the truth of (2) does not follow from the truth of (1).
Roger Bannister broke the four-minute mile on 6 May 1954. Before his birth it was surely possible that someone run a mile in under four minutes. But it does not follow that before Bannister's birth there was a runner for whom breaking the four minute barrier was a possibility. The possibility that there exist an F that is G does not logically guarantee that there exists an F that is possibly G. For it might be that every existing F is necessarily not G.
Another example. I cannot imagine a chiliagon (a regular polygon having 1,000 sides) but I can conceive one. Suppose conceivability entails possibility. Then it is possible that there be a chiliagon. But it doesn't follow that there is anything that actually exists anywhere in the universe that could assume the shape of a chiliagon.
So how can I get to the conclusion that some actual person, such as dear old me, can survive his physical dissolution and exist disembodied? Well, can't I imagine my existing disembodied as opposed to some person in general's existing disembodied? Isn't there such a thing as de re imagination? But how do I know that when I seem to be imagining my existing disembodied, I am really doing so as opposed to imagining some person's existing disembodied? How do I know that I am not imagining merely the instantiation of disembodied personhood as opposed to some definite actual person's disembodied existence?
Here we enter waters as murky as the Charles. I can imagine myself taking a walk through Boston's North End in search of an old haunt of mine, Piccola Venezia. The imaginability of this state of affairs is pretty good evidence of its possibility. But is this a de re possibility involving me or a de dicto possibility concerning some possible person?
Since no one will claim that I am incapable of revisiting the North End, there is no reason to doubt that when I imagine myself walking its streets, the possibility for which this imagining provides evidence is a de re possibility involving me, not some possible person in general. I am such that it is possible that I revisit the North End. So what reason could there be for denying that I am such that I possibly exist disembodied? Apparently, the only reason is a question-begging one: All actually existing persons are necessarily embodied.
My interim conclusion is the de dicto objection is nothing to worry about.