Tuesday, November 16, 2004

Edgar Foster returns (with Kripke)!

Edgar Foster returns, after a long absence, to raise a new question. The question, it turns out, comes from his recent reading and researches in the philosophy of former Princeton Professor, Saul Kripke (pictured left):

I hesitate to ask this question for fear of starting a new email thread. But what do you think about the proposition "If x is possibly distinct from y, then x is necessarily distinct from y"?
I would say: nonsense and bullwinckle. X could be possibly distinct from y without being necessarily so, could it not? Even if you want to eliminate altogether the element of seeming (to be) in possibility, this would seem to be so, in my humble opinion. For if x is possibly distinct from y, this has to mean that it is also possibly not distinct from y, which means that it can't possibly be necessarily distinct from y.
My question is based on Kripke's discussion in the last portion of Naming and Necessity [Amazon link]. What you say above makes sense. However, there are two points I did not mention in my original missive. First, Kripke has identities in mind. Second, he posits the view above with rigid designators in mind as well. For example, "Hesperus (x) is Phosphorus (y)." This proposition asserts that x is y. In this case, we know that x is not possibly distinct from y since x is y. But what if someone says, "Mental states are brain states"? The proposition is again one pertaining to identity. Kripke would also say that "mental states" and "brain states" (in the example above) rigidly designate their respective referents such that these designations obtain in all possible worlds.

He would then undoubtedly ask whether mental states (x) are possibly distinct from brain states (y). Kripke would go on to reason that if mental states are possibly distinct from brain states, then they are necessarily distinct from brain states in the same way that Hesperus, if possibly distinct from Phospherus, would have to be necessarily distinct from Phospherus since an entity that is possibly distinct from another entity cannot be (evidently) identical with that entity. So it seems that possibly not being distinct does not enter into the picture when we're talking about the subject of identity and rigid designators.

On the other hand, [Notre Dame philosopher, Peter] Van Inwagen (pictured right) takes Descartes to task for making a similar argument with respect to the RES COGITANS and the RES EXTENSA. Essentially, the French philosopher is arguing that his soul is possibly distinct from his body. Ergo, the soul is necessarily distinct from the body since it is possible for the soul to exist without the body, also possible for one to be certain that he has a spiritual substance while being equally doubtful that he possesses a RES EXTENSA.

Ok, fire away!
I guess I have some questions about what Kripke means here (& perforce you) by the distinction between "possibly distinct" and "necessarily distinct,"as well as by "rigid designations." First, I wonder to what extent a person's epistemic ignorance might play into the category of "possibly distinct." That is, does the distinction depend, at least in some cases, on a person's not knowing that x is necessarily distinct from y and therefore hypothesizing that it may be "possibly distinct"? Secondly, I wonder what "rigid designations" means in this respect too. Could something be "rigidly designated" yet fail to be rigidly self-identical or to exactly fit the rigid designation ontologically? This would seem to make a difference also.

Kripke says "Hesperus (x) is Phosphorus (y)." Okay, for the sake of an argument let me accept that this identity is ontologically determined and absolute. It would then make no sense suggest that x could be "possibly distinct" from y, would it; or, perforce, "necessarily distinct." Granted.

But when Kripke states "Mental states are brain states," he says something less clear. For we aren't entirely certain how mental states and brain states are related, though we have some non-empirical (pistical, for your benefit) commitments to the relative independence of mental states from brain states, as even epiphenomenalists have.

At this point one could meaningfully ask, it seems to me, whether mental states are "possibly distinct" from brain states, based on our ignorance as to how the two are related. A strict materialist would collapse the former into the latter, but even then might grant the former an epiphenomenal independence or seeming independence from the latter. But then it would seem that one could meaningfully ask whether, in this case, x is not possibly distinct from y without being sure whether x is necessarily distinct from y.

All of which would boil down to the question: what can Kripke possibly mean by his language of "rigid designation" here? Of course, if it is true in all possible worlds that x is necessarily distinct from y, then the identity of x and y is absolute regardless of whether we successfully recognize this identity and choose to "rigidly designate" it for what it in fact is.

I'm still not at all clear how "possibly distinct" is supposed to entail "necessarily distinct," in Kripke's usage. I can conceive of how darkness (x) could be "possibly distinct" from an overcast sky (y), as would be the case, for example, on a clear night. But I don't see how that would make x "necessarily distinct" from y (in this case), since one could easily conceive of an overcast day also being dark.