Phil 101: Causal Arguments against Dualism

What are the options for a dualist?

We began by discussing different pictures dualists could have about mental/physical causation.

We said the most natural, intuitive view is that sometimes physical happenings cause mental happenings (for example, stepping on a nail causes you to feel pain), sometimes mental cause mental (pain causes anger), and sometimes mental cause physical (the anger causes your face to get red and for your body to move and shout towards your roommate). Views that allow for all these possibilities are called interactionist forms of dualism. Descartes held a view of this sort.

There are more exotic, far-out options for the dualist too.

Some views deny that there are any causal interactions in either direction, not from physical to mental nor from mental to physical. Descartes’s follower Malebranche held a very radical form of this, called “occasionalism.” The details of what he said aren’t important for us.

Another view says that physical events can cause mental ones, but mental never causes physical. (This leaves open whether mental events can cause other mental events.) This is a view that’s called epiphenomenalism.

These alternative views ask us to accept: the hurting quality of your pain does not cause you to yell. The itchiness of your back does not cause you to scratch. These claims are hard to believe.

That’s why our discussion is going to focus on whether dualist interactionist views — the most natural view that a dualist could go for — are reasonable. Materialists have argued that these views are problematic.

van Inwagen’s “Remote Control” Argument

Suppose Alfred is operating a remote-control airplane, and a bird flies into the plane. This is likely to affect the plane’s performance, and Alfred’s ability to control it, but the crash won’t have any direct effect on Alfred. It won’t knock him unconscious, for instance. Similarly if the airplane flies through a cloud of corrosive gas.

This is the kind of situation we should expect if Alfred was something apart from his body. Why should hitting Alfred on the head cause him to become unconscious? Why shouldn’t it instead produce the following effects: Alfred feels a blow to his head, notices his body falling to the ground and no longer doing what he tells it, then he’s left floating in darkness but still conscious and able to muse about his condition. If Alfred’s body drinks alcohol, why aren’t the effects limited to Alfred’s body and his ability to control it?

The body and the mind don’t interact as we’d expect them to interact if the mind was something apart from the body, “remotely controlling” the body, as it were. The connection between them seems to be more intimate than that. The dualists owe us an explanation of why that should be so, if the soul is the independent substance they claim it to be.

How Do the Mental and the Physical Ever “Interface With” Each Other?

It is difficult for dualists to give a coherent account of how there could be any causal interaction between the mental and the physical. For according to the dualists, this would be a matter of some non-physical thing, a soul, interacting with physical things. It is obscure how things with the peculiar properties souls have could exert any causal influence on our bodies. The soul isn’t extended (it takes up no physical space); it isn’t in contact with any bodies; and in itself it has no physical properties (no mass or momentum or electric charge). By what means could something like that causally interact with our bodies?

In class, we talked about two arguments pressing this kind of challenge.

First, there was Princess Elisabeth of Bohemia’s challenge to her teacher Descartes. She argued that normally when one thing causes movement in a second thing, it has to push or touch the second thing. But how can a soul push or touch bodies, when it’s outside space?

Descartes thought we had to accept it as a fundamental, unexplained primitive idea that souls could causally affect bodies, at least at one central location. Elisabeth wasn’t satisfied with that.

The second argument was Kim’s “Pairing Problem.”

Consider that two guns A and B fire, and two people X and Y are killed. What could make it the case that the firing of gun A caused the death of X rather than the death of Y? The question may be a bit harder if gun A and gun B are physically the same as each other. (The same model guns.)

Note that we’re not asking how a detective could figure out or prove which gun killed which person. That’s an epistemological question. We’re asking something different. We’re asking, how can we make sense of there being an answer, even if no one ever knows what it is. Is there anything in reality that could make us be in the situation where it was gun A that killed person X and B that killed Y, rather than the other way around?

For guns, it’s natural to think that yes of course there’s an answer. There was a bullet that came out of gun A’s muzzle and then traveled through space until it hit X’s body. There wasn’t anything similar going on in the space between gun A and Y’s body.

And we’d expect a similar story to be available (that is, to have been out there in reality, even if no one is in a position to detect it anymore) whenever we have physical causation. The story about how one physical event causes another, and why it had this effect (death of person X) rather than this other effect (death of person Y) will have something to do with how the cause and the effect are related in space and time, and what happens in between them.

But now consider a case where we’ve got mental happenings in souls allegedly having effects on the physical world. Suppose we have soul A and soul B. It may make the case harder if they are mentally the same as each other. (Duplicate souls.) And we have one physical effect, that body C moves a certain way. (This is how Kim tells the story. He could have again had two bodies, but he just has one.) Now again we ask: what could make it the case that it was what happened in soul A that caused body C to move, rather than what happened in soul B?

Here the dualist can’t give the same kind of story they gave in the gun case. They can’t say “That’s explained by what happens in the spatiotemporal regions in between the happenings in soul A and body C.” They can’t say this because souls are supposed to be outside of space.

If we allowed the dualist to say that soul A affected some one part of the physical world, like Descartes’s pineal glands, then they could talk about what happens in space downstream from there. But how does that first instance of mental-to-physical causation work? Why was it what happened in soul A that affected body C’s pineal gland, rather than what happened in soul B?

Perhaps the dualist can come up with answers to these questions. But they do seem to be difficult challenges.

Epiphenomenalists avoid the questions as we’ve posed them because they deny that mental events ever cause physical ones. But dualists who take that strategy would have analogous trouble explaining why some physical events rather than others caused an effect in some soul.

Worries about Too Many Causes

Our last argument has to do with the notion of too many causes, often expressed as “causal overdetermination”. Many materialists believe this to be the most decisive objection or challenge to interactionist dualism.

Suppose these dualists are able to overcome the previous difficulties somehow. They find some way of explaining how it would be possible for there to be causal connections between the mental and the physical

Another problem for these dualists comes from the fact that we have good empirical evidence that nothing happens in or to a person’s body except what conforms to physical and chemical laws. The physical world seems to be causally closed: that is, for everything that happens in the physical world, there seems to be a wholly physical cause. There is no real scientific evidence that, in order to find a causal explanation of why your body moved in such-and-such ways, we have to appeal to “miracles” or any supernatural causes.

Maybe we have to make an exception for what happened at the start of time; but let’s ignore that.

As we discussed in earlier classes (here and here), there are debates in the foundations of physics about whether our world is “deterministic”, that is, whether how it is at one moment leaves open only a single physical possibility about how it will be the next moment. Arguably the notion of “causal closure” can be understood in a way that leaves open that our world isn’t deterministic. The philosopher who thinks the physical world is “causally closed” can say, well there has to be a physical explanation of why it was 90% probable that our world evolved in one way rather than another.

Now it may make it sound like we’re begging the question against the dualist here. If the physical world is “causally closed,” doesn’t that already say that there can’t be non-physical causes of what happens in the physical world?

No, we’re not yet assuming that. The label “causal closure” for this thesis can be misleading. All that we’re saying is that if something physical happened, then there is a wholly physical causal explanation of it. That leaves open the possibility, at least for the sake of argument, that there may be other explanations too.

All we’re saying is that if the dualists want to say that the mental has causal effects on the physical, then they’re going to have to say that there are non-physical facts about us that play a role in causing our bodies to move in the ways they do, and also there are wholly physical causes for our bodies moving those ways too. That is, they’re going to have to say that our bodies’ movements are overcaused. Our bodies’ movements have two separate causes, each of which is sufficient to make those movements occur or at least explain why they had the probability of occurring that they did. This would be like a case where two assassins simultaneously shoot someone, and each bullet was sufficient to cause the victim’s death. In such a case, his death would be overcaused.

If interactionism is true, though, then every time the mental facts about you play a role in causing your body’s movements, those movements would be overcaused. This would be overcausation on a systematic and wide-scale basis. The second step in the materialist’s argument against the interactionist is that it’s hard to believe that there is so much overcausation going on.

What pre-ordained harmony keeps the mental causes and the physical causes aligned or “in synch” with each other? What would happen if the mental causes and the physical causes got out of alignment? How would our bodies move then?

Some observations:

That link is to a Wikipedia article which is just for optional historical details.

Imagine that your friend Harry announces that he’s got telekinesis, or the power to move things without touching them, just by concentrating his mind in a special way (or using his wand, or whatever). Now in the real world, perhaps we’d already find that announcement incredible (unbelievable). But let’s make things easier for Harry and suppose that, in this scenario, we think some people actually are or might be telekinetic. But you never thought before that Harry was. He sees you have some doubts, and so offers to show his powers off. You say okay, why doesn’t he make the metal ball in this pinball machine roll into the flashing cup in the middle. So he scrunches his forehead, and lo and behold, the metal ball rolls into the flashing cup. Amazing! Except it turns out that this pinball machine also has lots of sensors and video cameras on it (like the black box in an airplane), and you sift through all the recorded information and it turns out that the metal ball was going to roll into the flashing cup anyway, just because of the direction and speed it was going, and how it bounced off the bumper on the left side, and so on. So Harry tries again. He scrunches his forehead and the metal ball goes through a loop-the-loop on the right side of the machine. Except, it turns out, that’s what it was going to do anyway, based on how it was already moving, and how the pinball machine is built, and so on. This keeps happening. Every time Harry tries to show off his telekinetic power, it turns out that the pinball was already on a course to do the same thing anyway, just because of the mechanics of the pinball machine. Harry says, Hey, that doesn’t prove he doesn’t have telekinesis, because maybe it just so happened that everything he made the pinball do, the machine also happened to make the ball do too. Some things have more than one cause. That’s true, you acknowledge, remembering the discussions of multiple assassins from your philosophy class. But probably, you’re going to be pretty doubtful at this point that Harry has the powers he claims to have.

In the same way, the materialist is doubtful that the dualist’s souls (which would be like Harry in the story) have the causal powers that the dualists claim they do, when all the movements of our bodies, our physical speech, and so on, can already be explained in physical terms (this would be like the pinball mechanics in the story with Harry).