Saturday, September 17, 2005

physicalism and mental events

Some people think that everything can be explained by, or reduced to physics. They are called physicalists or physical reductionists. The Maverick Philosopher has an interesting discussion of a famous physicalist named Daniel Dennett here and here.

Do you realize what a remarkable claim the physicalist makes? He believes that your personal feeling of satisfaction at making ten free throws in a row is nothing but the motions and physical properties of tiny particles. He doesn't just claim that it is caused by the motions and physical properties of tiny particles, he claims that it is nothing but the motions and physical properties of tiny particles in the same way, for example, that burning is nothing but the chemical combination of oxygen with a fuel. Burning isn't caused by this chemical reaction; burning is the chemical reaction.

But how could do you possibly get from particles to feelings? What sort of explanation could possibly reduce a feeling or a thought to a molecule? No physicalist has ever been able to give us a slightest hint in this direction, but they like to give analogies.

A very common analogy is heat. Heat doesn't seem very much like the motion of tiny particles. Is the warmth you feel when you hold your cold hands to a flame similar to tiny particles? Does it share properties with particles? Is there any apparent way to explain it in terms of particles? Of course not. At first it seems completely implausible that this feeling could be nothing but the motions of tiny particles, yet modern science tells us just that: (oversimplifying) heat is the random motion of molecules. The faster the molecules are moving, the more heat you have.

But this example doesn't prove what it is intended to prove because science hasn't actually reduced the feeling of warmth to the motion of molecules. When scientists wanted to study heat, the first thing they did was abstract out the feeling. They described heat in purely physical terms: heat causes solids and liquids to expand. It causes gasses to increase in pressure. It moves from one place to another in order to equalize an abstract property called "temperature" (defined as the property for which the difference is minimized by the transfer of heat). Work produces heat according to a fixed formula. Certain chemical reactions produce or absorb heat, again according to fixed formulas.

These are the phenomena that make up the scientific view of heat. These are the phenomena that are explained by the random motion of molecules. But what is implausible with any of that? If you want to explain why materials expand or why the pressure of a gas increases, it seems quite reasonable to talk about the motions of the tiny particles that make up the material or gas. If you want to explain what happens to the energy when macroscopic motion is dissipated, it seems quite reasonable to look to microscopic motions. And if chemical reactions involve the construction and destruction of molecules, then there is nothing remarkable about the idea that the resulting molecules might be moving faster or slower than the original ones.

So heat has been reduced to something that is not heat. It has been reduced to the motion of small particles, but only because it was first defined so narrowly that the resulting reduction was nearly inevitable. Science did not reduce the feeling of warmth to physics. Science took a purely physical phenomenon that is roughly correlated with feelings of warmth and reduced that physical phenomenon to smaller physics.

How could this analogy apply to consciousness? Well, it may be that scientists will some day find a physical phenomenon that is roughly correlated with feelings, thoughts, and other mental events. The current most likely candidate is some behavior of neurons. If scientists do find such a thing, then they will probably find physical causes for those physical events and thereby "explain" the physical events. But that would not be reducing the feelings and thoughts to physical events, it would be reducing the correlated physical phenomenon to other physical phenomena. Just as the feeling of warmth is not the same as scientifically-defined heat, the thoughts and feelings will not be the same as the scientifically-discovered behavior of neurons.

It is still impossible to imagine any way that feelings and thoughts might even in principle be reduced to physics. Mental and physical just don't have any properties that seem available to hook them together.
The only property they share is time (all events, physical or mental, happen in time), but just because two things happen at the same time, that is not enough to infer causality. You need a theory to tie them together and for that you need some other property that they share. In the case of heat, there were the properties of physical location and energy. What could there possibly be to tie physical and mental events?

Until the physicalists give us at least a potential answer to this question, their belief can be considered no more than a rather extreme leap of faith.

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