Thursday, September 01, 2005

The rational argument for substance dualism

In the third chapter of his book on Miracles, C.S. Lewis argued that rationality is only possible if we have a soul or a mind that is distinct from the brain. If all we are is physical stuff, then we cannot be rational. If Lewis is right, then it is self-refuting for a person to deny substance dualism. By denying substance dualism, he also denies the necessary preconditions for rational thought, which means that even his denial cannot be rational.

I can never hope to be as clear and articulate as C.S. Lewis, so I really urge you all to go to the library and read chapter three in his book. Or go to the Christian book store or Barnes and Noble and sit down on the floor and read it. It’ll just take you a few minutes.

In the meantime, I’m going to explain it as best I can. I think it meshes perfectly with J.P. Moreland’s argument. I had to tweak Moreland’s argument in the last blog. His argument went basically like this:

1. If the mind is merely a result or property of the brain, then we could not have free will.
2. We do have free will.
3. Therefore, the mind is not merely a result or property of the brain.

I had to tweak Moreland’s argument, because I don’t believe in libertarian free will like he does, and I don’t think libertarian free will is necessary to make the argument work. All that’s necessary is that the will have causal influence over the brain. My argument would look more like this:

4. If the mind is merely a result or property of the brain, then we could not act intentionally.
5. We do act intentionally.
6. Therefore, the mind is not merely a result or property of the brain.

What Moreland and I agree on, though, is that if the mind is merely the result or property of brain chemistry, then strict causal determinism is true. This isn’t hard to see. Let’s suppose that all that exists is physical stuff--matter and energy. If so, then all causal interactions in the brain are caused by the net forces acting on each molecule in the previous instant in time. Each brain state is caused by a previous brain state plus any other outside interference, such as signals reaching the brain through our senses, chemicals, or knocks on the head. Since each brain state is caused by something else physical, and every physical event is caused by previous physical events, all the events in the brain are determined by what caused them.

Since all the brain events are causally determined, all the mental events associated with those brain events are also determined. That includes the process of thinking and reasoning. The reason one person believes as he does and another person believes differently is because the causal interactions in one of their brains resulted in one belief and the causal interactions in the other’s brain resulted in a different belief.

Effects follow necessarily from their causes, so any person’s beliefs would have arisen whether there were good grounds for thinking it is true or not. It is completely irrelevant that one idea follows logically from another idea. Each idea is merely the effect of deterministic chemical reactions. Though we have a sense that we have arrived at a conclusion through sound reasoning, in reality, each step of the reasoning process is just the result of brain chemistry.

Lewis makes this clear by making a distinction between two senses of the word “because.” If we say Grandfather threw up because is ill, we are using the cause and effect sense of the word “because.” Being ill is what caused Grandfather to throw up. But if we say Grandfather is ill because he’s been throwing up, we are using the ground and consequent sense of the word “because.” His throwing up is the grounds upon which we think that he must be ill.

Our process of reasoning can only be valid if our conclusion is the consequent of good grounds. But if our conclusions are always arrived at by being the effects of causes, then they would arise whether there were good grounds or not. The fact that there may be good grounds for some conclusion is irrelevant to whether or not the conclusion is arrived at.

Strict physicalism is self-refuting, because if it is true, then we cannot be rational in believing in physicalism. The difference between a physicalist and a substance dualism is not that one is rational and the other is not, but that a series of blind causal interactions eventually resulted in one belief in the physicalist and a different belief in the substance dualist.

By affirming either position, we must assume substance dualism, because substance dualism is the only way we can make our affirmation rationally. In substance dualism, metal states (such as the belief that All men are mortal and the belief that Socrates is a man) can cause other mental states (such as Socrates is mortal) because one can mentally “see” the logical relation between these beliefs and draw a conclusion through mental processes.

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