How is Property Dualism Better Off than Substance Dualism?
Let's run through the objections to
Cartesian Dualism and see which fail to count as effectively against Property
There is an a priori difference: Assuming that a Cartesian ego would eo ipso have some immaterial mental properties, CD is logically stronger than PD. So one would need a reason for accepting CD over and above PD, and there must be at least one objection that applies to CD but not to PD.
(Nearly all the standard dualist arguments of the past fifty years are for PD, not for CD. Kripke's is one exception; he explicitly argues that he is not his body.)
On to the objections:
Queerness. First, nonspatiality:
Is it worse for an ego-substance to be nonspatial than for a property to
be? Perhaps a bit, since we don't much think of properties
as being spatially located in the first place. But in fact properties
are, arguably, so located. The color of a rubber ball is on its surface.
The ball's temperature is not uniform throughout, but every different degree
of temperature it has qualifies a very particular spatial location.
The ball's weight is located exactly where the ball is. We could
agree to locate immaterial properties in brains, but as I've argued in
class, we could and should also agree to locate immaterial egos in heads.
No real advantage for PD.
Nor as regards the allegedly weird properties (intentionality, subjectivity, etc.), because, obviously, they're properties.
Excrescencehood. What would nonphysical properties explain that an ego would not? Well, we do seem to be aware of properties that are problematic for materialism: intentional properties, qualia, "what it's like" and such. And if Hume is right, we are not aware of having (or ourselves being) immaterial substances. But these are not matters of explanation. As before, the canny dualist should reject the blithe Churchlandian assumption that the main purpose of mental ascriptions is third-person explanatory.
Interaction. No obvious difference here. How could a nonphysical property causally affect physical ones, any more than a nonphysical substance?
Neural dependence. Churchland says that that argument doesn't threaten PD at all, because PD "reckons the brain as the seat of all mental activity." But as we saw, the substance dualist can do nearly as well, by granting that finely tuned brain processing is constantly and absolutely necessary for mental activity. No substance dualist should suppose that the ego "is dependent on the brain for nothing more than sensory experiences as input and volitional executions as output."
Laws of physics. As with interaction: The nonphysical properties are supposed to have causal powers. Whatever problems CD has with the conservation laws or with general relativity, PD should have too.
Evolution. I'm still inclined to think that Bryce was right, and it's easier to imagine weird properties' emerging from complexity than whole individual substances' doing so.
Epistemology. Ryle was attacking CD, not PD, and impressionistically speaking, CD's ontology makes the epistemological problem look more grotesque. But I argued that his objection merely collapses into the interaction problem. Since PD has the interaction problem too, the epistemological objection is in fact no worse for CD.
Unity and individuation. Here PD does have an advantage. Since the property dualist regards the immaterial properties as properties either of the brain or more broadly of the human animal who has them, s/he need not worry about what identifies or unifies or individuates Cartesian egos, or about the vexed relation between an ego and a human body. The latter problems and hence the difference would diminish, though, if we spatialized the egos.
Verdict: PD is a little better
off than CD. But not so much better off that property dualists should
go on boasting that they're not so crazy as to be Cartesians.