Well, having got the boot for badgering dualists about their view of the world, I might as well carry on. In for a penny, in for a pound, I say. So for the next couple of posts I’ll discuss what all the fuss is about.
As I’ve said, there are some good-sized humps any dualist account has to get over, and the one that comes up most often is the problem of causal interaction. Let’s have a look.
The form of dualism that most believers espouse is called “substance” dualism. In philosophy, “substance” is a protean term, but generally a “substance” is something that has an independent existence of its own. It does not mean “matter” in the physical sense that it does in ordinary usage. So the position of the mind-body substance dualist is that there are two distinct substances here: the physical body, made of ordinary matter, and the mind, which is made of some sort of non-physical mind-substance.
(In the recent discussion at Bill Vallicella’s place I was taken to task for using the term “stuff” to refer to this alleged mind-substance; Bill suggested that my use of that word showed that I was still thinking of mind-substance as some sort of rarefied matter, and declared that I was unable to “think outside the materialist box”. That’s not what I was thinking, but I did use words like “vaporous”, and “ghostly”, as well — all of which have also popped up in Daniel Dennett’s many brusquely dismissive writings about dualism — which, I think, must have struck a nerve, given the severity of the reaction. Anyway, let’s be clear: to the substance dualist, the “substance” of which minds consist is not any sort of physical matter at all.)
So, if the mind is made of a substance that is not of the physical world, an obvious question arises: how does the mind do anything? How does it get the body to move, and how do the physical changes in the body get through to the mind? In short, how do they interact? This is the same problem that young children often point out when they watch Casper the Friendly Ghost on television: if Casper can fly through walls, how can he catch a ball?
To put the problem in more concrete physical terms, the causal interactions we see between physical objects involve some sort of transfer of energy from one object to another. This happens in all sorts of ways, including heat, chemical reactions, electromagnetic fields, and the ordinary “pushing” that we do to open a door (which is in fact mediated at the microscopic level by electromagnetic forces), but the point is always the same: matter interacts causally with other matter in observable ways, and there are books that need to be balanced. If I see a sofa scraping along the sidewalk, I will expect to see something pushing or pulling it. But how can an immaterial Mind accomplish this? Dualists do have an answer, but it is not a very satisfying one; it is, as one of our readers has described it, “just big enough to stand on”. Their idea is that our commonsense notions of causality are too narrow. Bill Vallicella sums it up as follows:
Let M be a type of mental event and B a type of brain event, and let m and b be tokens of these types. Perhaps there is nothing more to causation than this: m causes b =df (i) b follows m in time; (ii) Whenever an M event occurs, a B event occurs. On this regularity approach to causation, [the interaction objection to dualism] dissolves.
[That symbol “=df”, by the way, is a token for “means by definition”.]
Well, that’s a clever approach, and certainly takes some of the heat off. It’s fair enough; it just stands the materialist assumption on its head. The materialist says “well, this is how causation works, as far as we can see, so a nonphysical mind can’t interact causally with a material body.” The dualist, on the other hand, is saying, “well, my immaterial mind is obviously interacting with my body, so your model of causation can’t be right.” It seems to be a standoff, and the dualist philosopher can call it a day, and move along to other matters, free of the worry that there might be any empirical challenge.
But wait; there might be a problem down the road. Let’s say that neurological research, which is moving along at a fantastic clip, and gathering speed every day, were soon to reach the point where we could elucidate the entire neuromuscular process that generates a bodily movement. For example, let’s say I am standing on the sidewalk, and happen to glance skyward, where I notice that a flowerpot has been dislodged from a lofty windowsill and is plummeting toward me. Wishing to avoid a grievous injury, I step gracefully to the side.
What account shall we make of this? The light from the flowerpot impinged upon my retinas, which in turn sent a cascade of signals along my optic nerves, whence they were distributed to various parts of my brain. On the other, “downstream” side, neural signals were sent from my brain to the muscles in my legs, causing a sequence of contractions that neatly served the purpose of getting out of the way. But what happened in between?
For the dualist, the answer would be something like: the visual information traveled from the retinas into the brain, and at some point was “presented” to the Mind. The Mind, in turn, having contemplated in the light of abstract Reason the possible consequences of the body’s being struck on its apex by a falling flowerpot, and having arrived at a suitable plan, set in motion a chain of physiological events, involving motor-neuron excitation, that resulted in a graceful sidewise chassé, thereby sparing the physical half of the mind-body team a nasty knock on the head.
What are the implications of this view of these events? We’ll continue in the next post.