Saturday, February 19, 2011

Conjoined twins and pain

Wittgenstein once said that it may be possible for two different people to feel numerically the same pain. His example is that of conjoined twins (PI, SS 253). Consider two attached at the hip. They share a piece flesh joining their hips and associated nerve endings in that region of their bodies. A painful jab in that region should be felt by both twins since the associated nerve endings are shared. W uses this example to show that even something as private as pain is not inherently so. Many philosophers think that pain and other phenomenological experiences are by their very nature private but does W's example prove this view wrong?

It doesn't seem so if reductionism is true. For if pain is just some neuro-chemical activity in a region of the brain, say C1 of the somatosensory cortex, then since the twins have their own brains, they would experience their own pains. Even if reductionism is false, if mental properties like pain supervenes on physical properties such as brain regions and their associated neuro-chemical activities or those of entire neural networks, W's counter example still seems to fail. Consider a neural network composed of the nerve endings both twins share in the flesh connecting their hips together which we'll call N. N is attached to two different peripheral and central nervous systems. Each network only shares one region of overlap, namely, N, but are two different systems because they comprise different parts other than N. Overall activity in both systems would also be different.

So if pain is either reducible or supervenes on these different physical systems, they are not identical to each other.

To my mind, W does not deny the truth of either reductionism or mind-body supervenience. The only way to save W's "counter example" as far as I can see is if pain is severely localized to a single region of the body (where it is actually felt) but that seems highly implausible. Consider phantom limb pain where people feel pain where they once had limbs. People who experience this kind of pain experience it in their "phantom" limbs. The pain is thus "all in their heads." Alternatively, pain for these conjoined twins may be reduced or supervened on both their networks together. But that also seems unlikely.