I had a quibble about Dennett’s conservation-of-energy argument against dualism.  His argument, I’d agree, is pretty damaging for dualist theories that imply that the soul can affect the body, but there are at least three distinct forms of dualism that don’t:

1) The view that the soul is sort of like a field generated and sustained by the body, which takes its character at any particular moment from the character of the body at that moment.  Probably the most popular among dualists in academic philosophy these days.

2) The view that the soul’s essence is partially separate from that of the body–that the soul takes some of its character at any particular moment from the body’s character at that same moment, but that it also has some characteristics that aren’t derived from the body.  Maybe more of a theistic position than #1.

3) The view that the body and soul are entirely separate causally, and that their coincidence is the indication that the Creator made Creation to be well-ordered.  Leibnitz and I think a few Indic philosophers took this view, but it doesn’t seem to be talked about much anymore.

So it’s a pretty strong argument against two-way causality between body and soul–which might be all he really needs for the arguments he’s making.  But I don’t see it answering the more fundamental suspicion that there’s something above and beyond material reality.  Could you clarify how Dennett’s argument changed your mind?


You’re quite right that (1) and (2) escape Dennett’s argument unscathed.  However, the price for accepting them is that the soul becomes a mere spectator, with no ability to influence the world— even to move your eyes to look left.  What fun is that?  Or to put it more academically, what is the philosophical gain?  The appeal of dualism is that it fits our naive conception of ourselves.  But that conception includes the idea that we affect the world.

Of course, this might actually appeal to some people— Calvin, for example.  But I don’t get the appeal of such determinism anyway.  Theologically, I think it arises from the feeling that attributing causation to anything but God somehow diminishes him.  But it also makes him morally responsible for evil, which seems like a poor trade. 

As for (3), it’s possible, in the same sense that it’s possible that you’re a brain in a vat.  And it’s unbelievable for the same reason: the level of piddly detail required of the vat scientists or God is just too immense. 

I should note that there’s a fourth possibility: there is an energy input required to move the body, and we just haven’t noticed it yet.   Dennett’s argument isn’t a proof.   (One might even posit that another dualistic effect causes energy to disappear at about the same rate so that one couldn’t (say) detect the soul by testing the conservation of heat.   But it’s a useful heuristic in science that making phenomena hard to verify is a sign of pseudo-science.)

The other problem with dualism is that it’s something of a dead end, especially when it’s used as a rearguard fight against science.  Explaining cognition is a magnificent challenge for materialists, and has huge ramifications for robotics, computer science, psychology, medicine.  Even if it turned out to be wrong, we’ve already learned a lot and the failure would teach us more.  Dualism has no such program; you can posit a soul, but what can we learn from it?