- There is a very simple argument for the conclusion that the conscious mind cannot be separate from the physical brain.
The first premise tells us that my behaviour has a conscious cause, the second that it has a physical cause, the third that it doesn't have two causes—the only conclusion left is that the conscious cause is (part of) the physical cause.
- Conscious states have physical effects—for example, my conscious thoughts cause my behaviour.
- Physical effects all have sufficient physical causes (insofar as they are caused at all)—for example, my behaviour has neurophysiological causes.
- The physical effects of conscious causes are not all overdetermined (in the way that a death due to a simultaneous bolt of lightning and a bullet is overdetermined).
- (You might worry about what ‘physical' means in the above argument. This doesn't matter too much. There are many ways of understanding `physical' that will make the argument sound. Here let us just understand it as ‘inanimate'—states that can be found outside living bodies.)
- This argument might seem like a trick. If it's so simple, why hasn't everybody always been a physicalist? The answer is that premise 2—the causal closure of the physical—hasn't always been available. It will be helpful to look at this premise from a historical perspective.
- In the 17C Leibniz objected to Descartes' dualism precisely on the grounds that the causal closure of the physical left no room for an ontologically independent mind to influence the physical world.
- But this Leibnizian argument was undermined by Newtonian physics, which allowed other causes of physical effects than impact by matter in motion. For example, it allowed disembodied gravitational forces, and chemical forces, and magnetic forces—and vital and mental forces. (In the 18C there was a fierce debate between Albrecht von Haller and Robert Whytt on the relative roles of the forces of ‘irritability' and ‘sensibility'.)
- In the 19C scientists became convinced of the conservation of energy. This didn't rule out distinct mental forces, as long as they were ‘conservative' (But it did require them to be governed by definite force laws and so ruled out a-nomal spontaneity. This engendered a huge late 19C debate about free will.)
- The conviction that there are no distinct mental forces and only the four (three?) fundamental inanimate forces comes only in the 20C, with detailed intracellular research. Huxley and Hodgkin's 1952 model explaining nerve impulse transmission in electrochemical terms was crucial in this respect. Many philosophers presented arguments for physicalism based on the newly-established causal closure premise in the 1950s and 1960s.
- Of course, the argument for causal closure is inductive and does not conclusively rule out that some special extra force is operating somewhere in your brain. But ask yourself whether you think that it would be a sensible project for your Physics Department to start looking for this force.
Conference hand-out. This is effectively Section 1.2 of "Papineau (David) - The Case for Materialism", Chapter 1 of "Papineau (David) - Thinking About Consciousness".
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