Paranormal Phenomena and Substance Dualism
If you're going to be a dualist -- that is, if you differentiate the mental from the physical -- I think you ought to be a good old-fashioned substance dualist. You ought, in other words, to embrace the idea that there are distinct mental and material substances. The more fashionable form of dualism in analytic philosophy these days, "property dualism", which distinguishes mental from physical properties, as conceptually distinct, while denying that there is any distinctly mental substance, seems to me too far removed from the questions that we should care about in the dualism-materialism debate -- questions such as whether we have immaterial souls that could persist into an afterlife (property dualism, like materialism, says no), and whether our thoughts depend solely upon physical goings-on (property dualism, like materialism, says yes, for all practical purposes). I've not yet been convinced that I should care much about what would be the case in "logically possible worlds" where the laws of physics and psychology are suspended -- the sort of thing property dualists such as Chalmers want us to think about. (But if you are going to think about such things, Chalmers is a model of clarity and intelligence.)
The truth of substance dualism is empirically explorable, as the debate between materialism and property dualism (with its focus on the merely logically or "metaphysically" or "conceptually" possible) appears not to be. Of central relevance to the question, of course, is the dependency of our mental processes on how things stand in the material world -- on our brains in particular. The more it seems that mental life depends on and covaries with brain activity, the worse for substance dualism. With the advance of neuroscience, substance dualism isn't looking so good, I'd say.
However, there is one class of evidence that philosophers rarely explore and which, if it were to pan out, would spell serious trouble for materialism; that is "paranormal" or "psi" phenomena -- especially direct mind-to-mind communication (without a physical medium) and out-of-body experiences.
The evidence for paranormal phenemona is mixed. It is not as decisively negative as most contemporary academics tend to assume. The work of Daryl Bem (on direct mind-to-mind communication) and Pim Van Lommel (on out-of-body experiences in near-death situations) especially comes to mind.
Bem's classic "Ganzfeld" experiments (e.g. Bem & Honorton 1994 in Psych Bulletin) require a "sender" and a "receiver" to be sequestered in separate compartments; the "sender" is given a randomly selected image to concentrate on and to try to send; the "receiver" is to describe her thoughts and images aloud for 30 minutes. Finally the receiver is presented with four pictures (one the target) and asked to rate the similarity of each to her mentation during the 30 minute period. Results are generally above chance.
Bem, an eminent Cornell psychologist, knows how to design a study. Reading through his work, I generally think to myself, "If this were about anything else, I'd say this was a perfectly designed and utterly convincing study. He has controlled for everything." Carl Sagan was surely right in saying extraordinary claims require extraordinary evidence; but how extraordinary, exactly, is sufficient? Do we need to consider, for example, that Bem might simply be lying, or have been systematically deceived by unscrupulous collaborators and subjects?
Pim Van Lommel, similarly, has published work in the Lancet and elsewhere, work done in accord with typical scientific standards and suggestive of the reality and frequency of near-death experiences. Van Lommel has evidence that patients during cardiac arrest, with eyes closed and severely compromised brain function, were in some cases able to acquire otherwise unavailable information about happenings in the outside world (e.g., detailed descriptions of the what the doctor did with the patient's dentures) reported by the patient as having been seen from above. Van Lommel (personal communication) has even tried prospective studies of this latter sort of phenomenon, posting notes high in rooms where patients near cardiac death are being treated, notes facing the ceiling; but unfortunately, he reports, patients reporting near-death out-of-body experiences seem to be much more focused on their bodies and their religious experiences than on the contents of such notes!
I'm not saying we should accept Bem and Van Lommel; but I do think we should take them seriously. This is where I'd like to see the action in debates about dualism, rather than on questions such as the conceivability (or not) of various possibilities (e.g., "zombies"), if one suspends the laws of physics!