Substance dualism and mental causation Michael Lacewing

Substance dualism Dualism: there are two sorts of substance, mind (or soul) and matter –Minds can exist independent of bodies –Mental properties are properties of a mental substance Materialism: there is just one sort of thing, matter –Mental properties are properties of a material substance

Mental causation Descartes: the mind is just thought, not in space; matter is just extension, in space The problem: how could one possibly causally affect the other? –Mental causation: thoughts, desires and other psychological states cause both other mental states and changes in the body (e.g. movement)

Princess Elisabeth’s version Physical things only move if they are pushed. Only something that is extended and can touch the thing that is moved can exert such a force. But the mind has no extension, so it can’t touch the body. Therefore, the mind cannot move the body. Reply: This isn’t an accurate account of why things move –E.g. force of gravity doesn’t need contact

Development The movement of a physical object is only initiated by some physical force, exerted at some point in space. If dualism is true, then the mind is not in space and cannot exert any physical force. Therefore, either dualism is false or the mind cannot cause (any part of) the body to move. The mind can cause the body to move. Therefore, dualism is false.

Conservation of energy The law of the conservation of energy: in any closed system, the total amount of energy in that system remains unchanged. The universe is a closed system. Therefore, total amount of energy in the universe remains unchanged.

Conservation of energy If the mind, as a non-physical substance, could move the body, the total amount of energy in the universe would increase. Therefore, if the mind could move the body, the law of the conservation of energy would not apply to the universe, and the universe is not a closed system. Therefore, because what is changing the physical energy in the universe is not itself physical, physics cannot give us the complete, correct account of physical energy in the universe. –Physics is wrong to think that physical movement can only be caused by a physical force.

Neuroscience Movements of the body are caused by physical events in the brain. We have no evidence of the mind changing what happens in the brain. Reply: we have no evidence that the mind does not change what happens in the brain –If dualism is true, then some brain events have no physical cause The empirical evidence is not against dualism.

Epiphenomenalist dualism Perhaps substance dualism is true, but there is no mental causation –This is epiphenomenalism The claim is very counterintuitive The claim threatens to undermine choice and responsibility for our actions