Tuesday 6 January 2015

Kripke's Argument for Dualism

  1. It's possible for there to be mental states without brain states
  2. Therefore, mental states are not identical to brain states
Since mental states (e.g. pain) and brain states (e.g. c fiber stimulation) are ridged designators—referring to the same object in every possible world—the inference from (1) to (2) is valid. Kripke thinks, and I want to agree, that at face value premise (1) seems to be true. And so the materialist, wanting to say that mental states reduce to brain states, is faced with the challenge of explaining away this intuition.

The materialist might meet Kripke's challenge by rallying behind other well established identity claims, considering them partners in crime. If we're not prepared to entertain doubts about, for example, water being identical to H2O, or lightening being identical to the discharge of electrons, or heat being identical to the excitement of molecular particles, then why should we doubt that mental states are identical to brain states? While the materialists theory isn't nearly as well evidenced as these other identity claims, it's still the best explanation of why mental states are so perfectly correlated to brain states. But surely the intuition that minds could persist in the absence of brains is no stronger than the intuition that water could exist in the absence of H2O, or that lightening could occur without a discharge of electrons.

But Kripke has an answer to this. He suggests our intuitions about the possibility of there being water without H2O are misguided. It's plausible, he thinks, that we are mistaking the one possibility with another: that there is something that is phenomenologically identical to water (that we have no way, short of a chemical analysis, to distinguish it from the stuff that fills our rivers and lakes and oceans) when there isn't any H2O. But, as Kripke argues, such an explanation misses its mark when applied to the materialists reductionist theory of mind. There cannot be anything that is phenomenologically identical to pain, and yet isn't pain. If someone thinks they're in pain, or is having an experience of being in pain, then they are in fact in pain. Pain, in other words, cannot be illusory. And so the materialist cannot use these other well established identity claims as partners in crime: the evidence incriminates him alone.

Kripke thinks he's successful in defending, at the very least, a presumption against materialism. But I think there's a further response the materialist can give. Granted, it's intuitive that unembodied minds could exist. But it's no less intuitive that the materialists theory could be correct, and that mental states could actually be identical to brain states after all. But of course, if mental states are identical to brain states then they are necessarily so, and premise (1) of Kripke's argument must be false. We thus have two equally valid but opposing intuitions. What do we do with them? I suggest they cancel each other out, and leave us without any presumption either for or against materialism.

But then we are back to where we started, with no reason to reject a materialist theory of mind and some fairly significant reason to accept it: along with ontological parsimony, the identity of mental states and brain states offers an attractive explanation of the appearance of supervenience. It seems, then, that if anything at the end of the day we are left with a strong presumption in favour of a materialistic reductionism of the mind.