Milinda’s Questions

There’s a very interesting discussion going on over on Bill Vallicella’s Maverick Philosopher about the “standard arguments” against mind/body dualism. Bill starts out by quoting Elliot Sober:

If the mind is immaterial, then it does not take up space. But if it lacks spatial location, how can it be causally connected to the body? When two events are causally connected, we normally expect there to be a physical signal that passes from one to the other. How can a physical signal emerge from or lead to the mind if the mind is no place at all?

Bill paraphrases this argument as follows:

Now what exactly is the objection? It seems to be this. If mind and body belong to mutually irreducible ontological categories, and yet minds and bodies interact causally, then this violates conservation principles. For example, if my intention to paint the bathroom is an irreducibly mental state that causes the states of the brain that control the motions of my limbs, then there is presumably a transfer of energy into what is supposed to be a closed physical system in violation of the principle of conservation of energy.

There’s a problem here, of which several of Bill’s commenters are aware; but it’s pointed out most pithily by Eric Thomson in a comment over on Victor Reppert’s Dangerous Idea:

Valicella responds to one argument (violation of certain conservation laws), while Sober’s claim is about the spatiality of causal relations, not violation of conservation laws.

Valicella seems to have quoted the wrong section of Sober or something.

What’s being called here the “spatiality of causal relations argument” against dualism is one of the oldest objections to dualism. It’s expressed very well in Justin Skirry’s article on Descartes in the Internet Encyclopedia of Philosophy. Skirry reminds us that the objection was originally voiced in Pierre Gassendi’s Fifth Set of Objections and Replies to Descartes original Meditations, as well by his correspondent Queen Christina of Sweden. Here’s Skirry’s summary:

It is this problem of voluntary bodily motion or the so-called problem of “mind to body causation” that so troubled Gassendi and Elizabeth. The crux of their concern was that in order for one thing to cause motion in another, they must come into contact with one another as, for example, in the game of pool the cue ball must be in motion and come into contact with the eight-ball in order for the latter to be set in motion. The problem is that, in the case of voluntarily bodily movements, contact between mind and body would be impossible given the mind”s non-extended nature. This is because contact must be between two surfaces, but surface is a mode of body. . . . Accordingly, the mind does not have a surface that can come into contact with the body and cause it to move. So, it seems that if mind and body are completely different, there is no intelligible explanation of voluntary bodily movement.
. . .
A similar problem arises for sensations, or the so-called problem of “body to mind causation.” For instance, a visual sensation of a tree is a mode of the mind alone. The cause of this mode would be explained by the motion of various imperceptible bodies causing parts of the eye to move, then movements in the optic nerve, which in turn cause various “animal spirits” to move in the brain and finally result in the sensory idea of the tree in the mind. But how can the movement of the “animal spirits,” which were thought to be very fine bodies, bring about the existence of a sensory idea when the mind is incapable of receiving modes of motion given its non-extended nature? Again, since the mind is incapable of having motion and a surface, no intelligible explanation of sensations seems possible either. Therefore, the completely different natures of mind and body seem to render their causal interaction impossible.

An apparently anonymous commenter points out that this objection may be considerably less compelling now than it was in Descartes’ time, given contemporary views of the nature of matter:

[The] objection to interactive dualism is based on the idea that physical-physical causation is more intelligible than mental-physical causation because physical objects, when they interact causally, touch each other. Although this was true in early formulations of Newtonian (and Cartesian) physics, it isn”t true in contemporary physics where the field is arguably the primary sort of entity. One place we can see this is in the repelling of one electron by another even when they are not touching.

Good point; but aren’t fields still spatial in nature? (Although I don’t know whether we want to call them entities or properties or whatever.) In which case can’t the “spatiality objection” be rephrased in a nonobjectionable matter? Namely, that physical/physical causation can be explained in a manner that makes reference to spatiality, in a way that doesn’t seem applicable to mental/physical causation?

At any rate, Suppose we grant that physical/mental causation is no more problematic than physical/physical causation — or even if it is somewhat more problematic, we still have to admit it into our best explanation of the world? What follows? Franklin Mason recognises that there’s still a problem for the dualist:

In the case of mental-physical causation, we have a related problem. It isn’t that we have action at a distance. But still the cause does not touch the effect. Thus it seems unintelligble why the cause should latch on to just this object (or whatever) and no other. Why should my mind control my body and not yours? Why don’t our minds switch the bodies they control?

Obviously, there are a number of distinct pro- and antidualist arguments at play in this discussion (exactly how many depends on how you differentiate the arguments.) Seems to me that in addition to the two mentioned already (the “spatiality argument” and the “causal-closure argument”, we can usefully distinguish a third: the “explanatory-adequacy argument.” Here’s how Bob Koepp puts it:

[A] much more serious challenge to interactionist substance dualism is posed by the likelihood that once all the physical processes are sorted out, there’s nothing left in the physical realm to be explained by appeal [to] mental causes. Unless there’s some recalcitrant physical phenomenon for which we can’t find appropriate physical precursors, there wouldn’t seem to be any reason to invoke mental-physical causation.

It seems to me that, from the broadest perspective, all of these objections to dualism can be conceived of as versions of the explanatory-adequacy objection. It’s like this: at the highest level of abstraction, the claim made by the dualist is, “Once we have a complete physical explanation, there is (or will be) nothing left to explain.” When we try to think about it more concretely, though, it’s not so clear what the antidualist would count as “a complete physical explanation”, whether we have such explanations now, or how close we are to having them. It’s not even clear whether the claim concerns token-token or type-type explanations, or if the latter, what level of generality we’re talking about. Therefore, it seems to me that the dualist, insofar as she finds the explanatory-adequacy objection compelling, assumes that we already know in broad outline what an adequate physical explanation will be. If you then flesh out the objection with a particular picture of what physical explanations are like, you get versions of the other two major objections. For example: if you assume that any adequate physical explanation will conform to the causal closure of the physical, then you have the causal-closure objection. Or if you add the assumption that any physical explanation will be an explanation in terms of spatial properties, then you have the spatial objection.