IV. Arguments against Dualism
A. The Problem of Other Minds
1. Two Interpretations
The Problem of Other Minds: Interpretation
1. If CD is true, then there is no reason to think that other people exist.
2. There is reason to think that other people exist.
3. Therefore, CD is not true.
Dualist Reply: Deny P1:
Even if CD is true, and there is this division between mind and body, there is still some reason to think that other people exist (i.e., there is still some reason to think that there are other minds). Here's why. Even given CD, I still know that I have a mind. And then I can see the correlation with events in mind and my behavior. When I feel pain in my mind, I say Ouch and jump around. When I am nervous in my mind, I start to bite my nails. When I am happy in my mind, I smile. So I witness some causation that goes from states of my mind to states of my body. Now, in others I see certain states of their body. Given the correlation I observed in my own case, I now have some reason to think that they, too, have minds, and that it is these events in their mind that is causing the events in their body. So I am drawing an analogy from my own case. (This is sometimes called the Argument from Analogy.)
Let me give an example of this sort of induction at work somewhere else. Suppose I'm traveling in some unknown part of the world and I happen upon a fruit tree I've never seen before. I want to know what is inside the fruit that hangs from it. Is its pulp sweet or not. So I pull one off, cut it open, observe its color, its odor, its consistency. Then I take a bit to see how it tastes. Now, can I be absolutely certain that the others will be like this inside? No. But do I have some reason to believe they will be like this inside? Yes, I do. Knowing how one of them is inside is pretty strong evidence that others will be that way, too.
So even though I never directly observe other minds, there is still reason to think they exist, and hence reason to think other people exist. So P1 is false.
In response to the Dualist reply to the above version of the argument, Ryle might offer the following:
The Problem of Other Minds: Interpretation 2:
1. If CD is true, then we cannot be absolutely certain that there are other people.
2. We can be absolutely certain that there are other people.
3. Therefore, CD is not true.
Dualist Reply: Deny P2:
Of course we can't be absolutely certain that there are any other people. Didn't you read my book?!, Descartes might say. For all we know we're being deceived by an evil demon, or for all we know we're in the Matrix. For all we know all of this is a hallucination. I cannot be absolutely certain that there are physical objects, that I have a body, that the external world exists at all. So of course I cannot be absolutely certain that there are any other people.
B. Causal Arguments Against Dualism
Many arguments against dualism attack Clause (e) of CD, the one that says that our immaterial mind and physical body enter into two-way causal interaction.
1. The Inconceivability of Causal Interaction
The Inconceivability of Causal Interaction
1. We have no idea how a non-physical substance (an immaterial mind) could cause a physical object to move.
2. If 1, then we have no idea how CD could be true.
3. If we have no idea how CD could be true, then we should not believe CD.
4. Therefore, we should not believe CD.
P1: The general idea behind P1 is this. If dualism is true, then mind and body are totally unlike each other -- so much so, that it is difficult to see how one of them could cause anything in the other. Bodies -- physical objects -- are heavy, klunky, exist here in space. They require force to be moved. Immaterial minds, on the other hand, are totally unlike this -- they strike one as wispy and ethereal, since they consist merely of thought and no matter or bulk. They are not extended in space, and indeed may not even be located in space. How, then, can something so different, that perhaps exists in some remote otherworldly realm, cause things to happen here in the physical world? How can the mind have any causal influence on the body? By what means could something like that causally interact with our bodies? We have no idea the mechanism by which such causation could occur.
Contrast this with a case in which we do have some idea of the mechanism. Here's one event: pressing the brakes in your car. Here's another: your car stopping. The first event causes the second. Do we have any idea of the mechanism by which such causation could occur? Yes! Here is one way it might occur: when the brake is depressed, this causes a cable to be pulled, to which the brake pedal is attached. The cable is connected on the other end to some calipers or whatever that squeeze down on a brake pads which squeeze down onto a disc, which is attached to the wheel. The friction between the pads and the disc causes the disc to slow down, hence causing the wheels to slow down and eventually stop.
Now, maybe this isn't exactly the right mechanism, or maybe your car has a different one. But the point is simple: we can form a coherent picture of some mechanism by which pressing brake pedal could stop a car. We can do this even if we're not auto-mechanics.
But with mind-body causation, we can form no such picture. We have no idea how it could happen. It's like magic. How, for example, could a desire in your mind move your body? It's mysterious.
P2: Well, it is a part of CD -- clause (e) to be exact -- that such causal interaction occurs. So, IF we have no idea how it could be true that such causal interaction occurs, we have no idea how CD could be true. If a theory has a part that you don't understand, then you don't understand the theory.
P3: It seems to be a principle of rationality
that if you have no comprehension how some theory could be true,
then you shouldn't believe it. If you should believe that
something is the case, then you should at least be able to coherently
2. The Argument from the Causal Closure of the Physical
3. Remote Control Argument
C. The Continuity of Nature Argument
D. The Argument from Parsimony