In this video, philosopher and Christain theologian Alvin Plantinga outlines his modal argument, which in my view successfully establishes that he is not identical with his brain or body.
He interprets this to mean that he is something more than physical, and presumably that he has a soul. Physicalism refuted? Nope!
The outline of the argument goes like this (in my words).
- If A and B are the same thing (identical), then whatever is true of A is true of B
- I can conceive of having my body exchanged for another and still being me
- I cannot conceive of having my self exchanged for another self and still being me
- Therefore my body and my self are not identical
The usual response of atheists and physicalists to this argument is that you can't use conceivability to prove anything. One can conceive of all kinds of impossible scenarios which have no bearing on reality. Plantinga is often ridiculed for thinking he has proven anything with only his ability to imagine counter-factual scenarios. See the following video for an example.
For a more nuanced consideration of the problems with the argument which arise from its reliance on conceivability, read Brad Lencioni's blog on the topic.
The trouble is that refutations such as this rely on Plantinga's concept of himself being mistaken, and that it is not possible for Plantinga to exist in a different body.
I don't think that's true.
As I have discussed before, I do not believe that we are identical with our brains or our bodies, but that does not mean that I am a dualist.
Rather, I think that it is a misunderstanding of materialism/physicalism to insist that everything is synonymous with discrete physical entities. This is simply not true, and obviously so. In particular, it is not the case with patterns.
Consider an ocean wave. At any one instant, it is composed of water molecules, but as the wave moves, the water molecules composing it change. Yet we regard it as the same wave the whole time.
Plantinga's argument simply shows that the wave is not identical with the water molecules that compose it. If this is supposed to be a problem for physicalism, then he has a very simplified and misconstrued view of physicalism!
A wave is a pattern the constituent parts of which change over time. The wave's identity is wholly independent of which particular water molecules make it up. We can conceive of this same wave being composed of entirely different water molecules, or even of oil or other substances.
A piece of software is also a pattern which is hosted on a physical substrate - computer hardware. The same program could be run on any computer, so a program is not identical with the computer that runs it.
(In a way, this relates back to my refutation of John Searle's Chinese Room argument. The hardware in the room, namely Searle himself, is not the same thing as the system it supports. It is no surprise that he doesn't understand Chinese because he is not the one doing the understanding!)
Software is to a computer as a mind is to a brain. It is clear to me that Plantinga identifies with his mind rather than his body/brain, and so while his conclusion is correct, it is irrelevant and unsurprising.