Tuesday, 20 November 2012

In Defence of Strong AI: The Modal Argument Refuted

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).

  1. If A and B are the same thing (identical), then whatever is true of A is true of B
  2. I can conceive of having my body exchanged for another and still being me
  3. I cannot conceive of having my self exchanged for another self and still being me
  4. 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.


  1. I liked this post, for it helped me get a grasp of your conception of what mind is--which is interesting.

    My one critique is (perhaps) the logical oversight that the conclusion of Plantinga's argument may be true, but his premises do not prove so; thus his argument is still unsound.

    So one (including yourself) might agree with Plantinga's mind/body distinction, but still ought to reject his argument. Because it is not a sound deduction of anything.

    1. I think I would be a bit more forgiving of his argument.

      Strictly speaking, his argument does prove that his "concept of self" is not the same as his "concept of body". His argument is valid, I think, for anybody who would agree with his concepts, and in particular for anybody who can imagine being separated from their current body.

      While deriving possibility from conceivability may be dubious, when you're talking about the identity of concepts I think it's valid to work from conceivability alone.

      So, if you can conceive that Superman and Clark Kent are not the same person, then it is clear that those are two distinct concepts.

      So Plantinga is right: if you can imagine being separated from your body, then it is clear that your concept of self is not the same as your concept of body.

      As I write this, in mid-post, it occurs to me I have inadvertently revealed a gap in Plantinga's logic. One could grant him that the concepts are different and still be of the position that in reality they happen to be the same thing (i.e. Superman happens to be Clark Kent). Oh well!

      It's possible that the US President could be someone other than Barack Obama. It is not possible that Barack Obama could be someone other than Barack Obama. Therefore, by Plantinga's logic, the president cannot be Barack Obama.

      But who cares about concepts, right? We care about reality. We care about your actual self, your actual body. Are they the same thing?

      I would say that whether your actual self is identical to your actual body or not is a meaningless question, because in my opinion there is no universally accepted definition of what constitutes personal identity or selfhood. You have to take a concept of self as granted for the question to have any meaning.

      I wrote a whole series of blog posts about the false intuition of the concept of selfhood called "Essential Identity" if you want to see my thoughts on that subject.

    2. Just to defend Plantinga against my own criticism above (I love arguing with myself, it seems...)

      It's hard to imagine how one could be capable of conceiving of existing without one's body, while simultaneously maintaining the belief that you are identical to your body.

      It's much easier to imagine the president being Mitt Romney while believing that the president is Obama.

      So I think there's something wrong with my analogy, although I'm not clear what. I think it may hinge around the difference between believing two concepts are actually the same (the self is the body) and two concepts happen to refer to the same object in this world (the president is Obama).

      I think perhaps Plantinga's argument may not be incorrect in this respect. I think Plantinga's argument probably does successfully show that if you can imagine existing without your body, then it is not reasonable to believe that you are identical to your body.