Dualists' Troubles with Common Sense

Is there a psychology of metaphysics? Yes! And one of its high-profile results seems to be this: Ordinary people (or at least the less scientific among them) are metaphysical substance dualists. They think that material bodies are one thing and immaterial souls quite another. Paul Bloom argues for this on cross-cultural and developmental grounds. Brian Fiala, Adam Arico, and Shaun Nichols propose a cognitive mechanism to explain it. And it certainly seems to fit with widespread belief in God, the afterlife, etc. You are an immortal soul "fastened to a dying animal".

But if you've read your history of philosophy, you might wonder this: If dualism is just common sense, why are dualistic metaphysical systems always so bizarre? Leibniz sees a universe of "monads" that move in pre-established harmony with each other but do not causally interact. Malebranche thinks nothing has any real causal power except for God, who constantly creates the universe anew at every moment. Descartes, whose "causal interactionist" dualism might initially seem a reasonable candidate for common sense, held that nonhuman animals were mere mindless machines, incapable of conscious experience. (It's hopefully not true that Descartes tossed a cat out of a window in Leiden to illustrate his belief in this.) "Common sense" philosopher Thomas Reid attributed immaterial souls to vegetables and denied that material objects had the power even to cohere into shapes without the regular intervention of immaterial souls on their behalf.

Here's my explanation of the bizarreness of dualist metaphysical systems: Commonsense opinion is not straightforwardly substance dualist. Rather, commonsense opinion about the metaphysics of mind is an incoherent mess. Thus, it's impossible to develop a detailed, coherent dualist metaphysics that respects all the inclinations of common sense.

There are at least two broad issues on which dualistic metaphysical systems have repeatedly stumbled against common sense: the causal powers of the immaterial mind and the class of beings with immaterial minds.

The causal powers issue can be posed as a dilemma: Does the immaterial soul have the causal power to affect material entities like the brain? Both yes and no answers lead to trouble. If yes, then physical entities like neurons must be regularly and systematically influenced by immaterial events. A neuron must be caused to fire not just because of the chemical, electrical, and other physical influences on it but also because of immaterial happenings in spiritual substances. Either events in the immaterial realm give it some physical or quasi-physical push that leads it to behave other than it would without that immaterial push -- which seems to violate our commonsense ideas about nonmiraculous causes of physical movement (and a minimal commonsensical deference to mainstream physics and neuroscience) -- or the immaterial causal influence somehow operates on the physical despite the fact that the physical would behave no differently absent that influence, which seems an equally strange view. Suppose, then, the other horn of the dilemma: The immaterial soul has no causal influence on physical events. If immaterial souls do anything, they engage in rational reflection. On a no-influence view, such rational reflection would have no power to causally influence the movements of the body. You can't make a rational decision that has any effect on the flow of the physical world, including the movements of your own body. This again seems bizarre by the standards of ordinary common sense.

The scope-of-mentality issue can be posed as a quadrilemma: Either (a.) among Earthly animals, only human beings have immaterial souls and they have those souls from birth (or maybe conception), or (b.) there are sharp boundaries in phylogeny and development between ensouled and unensouled creatures, or (c.) whether a being has an immaterial soul isn't a simple yes-or-no matter but rather a gradual affair, or (d.) panpsychism is true, that is, every being has, or participates in having, an immaterial soul. Each possibility violates common sense in a different way. Since on a substance dualist metaphysics of mind, the immaterial soul is the locus of mentality and conscious experience, option (a) denies dogs and apes mentality and conscious experience, contrary to what seems to be the clear opinion of most of humankind. Option (b) requires sudden saltations in phylogeny and development, which seems bizarre given the smooth gradation of differences in behavioral capacity, both developmentally and across the range of non-human animals, and given the work the immaterial soul must do if it's not to be otiose. Option (c) appears incomprehensible from a commonsense point of view: What would it mean to sort of, or kind of, or halfway have an immaterial soul? (Would you sort of go to Heaven? Even Dog Heaven, which might be a "sort of" Heaven, seems to require dichotomously either that dogs are materially instantiated there or that they have some immateriality that transcends the grave.) And despite a certain elegance in panpsychism, the idea, in option (d), that even vegetables and bacteria and proteins and thermostats have immaterial souls, or alternatively that they participate in a single grand immaterial soul, seems bizarre on the face of it, by the standards of ordinary common sense.

Any well developed metaphysical substance dualism must make choices on such matters. And all the choices seem weird. If you think otherwise, I suspect philosophy has dulled your sense of what's weird. But weird does not imply false! We have good independent reasons to think, on physical and cosmological grounds, that the world is a pretty weird place, not well matched with our commonsensical intuitions about what must be so.