Aside from the fact that Dr. Plantinga isn’t quite sure how many legs a beetle has–come on, eight, really?!?–I think he presents a really good argument against physicalism.
The argument runs something like this:
1. If I am my Body, then anything possible with regard to me is also possible with regard to my body.
2. It is possible that I exist when my body does not exist.
3. It is not possible that my body exists when my body does not exist.
4. Thus, “I exist without my body” is something possible with regard to me that is not possible with regard to my body.
5. Therefore, I am not my body.
The argument demonstrates a discernible difference between the body and the self. But does it matter that we are talking about mere possibilities here? Plantinga’s point is that there is no possible world where a body exists without itself. Yet, it does not seem logically impossible to imagine a possible world where the self exists without its body. We take such stories to be supernatural, fantastical, or fictional, but not logically incoherent. So, it seems reasonable to suppose the logical possibility of a disembodied self.
This means that proving an identity relationship between the self and the body requires a lot more than empirically proving a causal relationship between physical states and mental states. One must also prove that it is logically incoherent to suppose that there are any possible worlds where the self is disembodied. So it seems that while this burden is heavily placed upon the physicalist, the supernaturalist can merrily go along believing that she is her soul. Right?
Not so fast, my friend Shaun Miller has pointed out to me that this argument, if anything, proves too much (Shaun was inspired by Shelly Kagan, ff about 43 min in for the appropriate part). Kagan points out that we could imagine that the same body is possessed by different souls. His point is not that we are not our soul, but that our soul doesn’t seem sufficient to establish personal identity. As far as I can tell, Shaun’s response to Plantinga is original, and quite difficult to overcome. He points out that we could substitute just about anything in the argument, including the soul, and prove it to be non-identical with the self. Does this mean that I am not my soul?!? My initial reaction to this was, “Well, it’s just not possible that I exist without my soul, since I am my soul.” But now I’m guilty of special pleading. This fallacious soul-ution is to stipulate that “soul” is simply defined as “self”. But then we have just stipulated our way to victory, which is not very satisfying. What would prevent the physicalist from stipulating “body” as “self”? We’re back to square one.
Upon further reflection, I think the argument achieves something. It proves that unless we have good reason to think that it’s not possible for X to exist when Y doesn’t exist, then we don’t have good reason to think X and Y are identical. I have no good reason to think I am my body, because I think it is at least logically possible to be disembodied and survive. But then I should be willing to bite the bullet and concede that I have no good reason to think I am my soul. So be it. I have no good reason to think I am my soul either. As I said before, we could substitute just about anything for body–just about. However, I cannot substitute “self”. Whatever “self” is, it cannot both exist and not exist, at the same time, and in the same possible world! So I do have good reason to think at least this… I am myself.
But is this an adequate response? Are there other problems with the argument that I am not mentioning here?