Mind-Body Problem

Descartes and Dualism

The most obvious strategy for solving the problem is to insist that minds are bodies or some proper part of the body, perhaps the brain or the central nervous system. This position, the identity theory, claims that minds and brains are identical. René Descartes famously argued that the identity theory must be false. According to Descartes, it is conceivable that minds exist without bodies, and so it is possible that minds exist without bodies, and so minds are not bodies. Now the relationship between what is conceivable and what is possible is tricky and has attracted much attention. It is dubious that Descartes is licensed to move from conceivability to possibility. But what of the move from the notion that it is possible that minds are not bodies to the conclusion that minds are not bodies? That move might seem a non-starter. Much that is possibly the case is not actually the case. But what Descartes assumes, at least implicitly, is that if minds and brains are identical, then they must share all of their properties in common. Descartes assumes that whatever is identical must be indiscernible: For any two objects, x and y, if x is identical to y, then for any property x has y has, and vice versa. And so if minds are brains, then whatever property the one has the other also has. But it is not possible for brains to exist without brains. And so, if minds are brains, then minds could not exist without brains. Thus, if it is possible for minds to exist without brains, then it follows that minds are not brains.

Descartes’ response to the mind-body problem is that minds and bodies are radically different kinds of things; the latter material, the former immaterial. But Descartes’ solution, dualism, introduces two new problems. The first challenge is to make intelligible what an immaterial thing might be. The second problem, related to the first, is the problem of mental causation: How do minds causally interact with bodies? This problem for Descartes is especially acute: How do immaterial substances interact with material substances?

The contemporary version of the mind-body problem is not cast in terms of substances and is often cast, instead, in terms of laws, states, properties, or events. In terms of properties, for instance, the mind-body problem is this: How are mental properties related to physical properties? That is, how are mental properties related to the properties of interest to the natural sciences? And the problem of mental causation, in its modern guise, concerns the causal closure of the physical. It is commonly presumed that the laws of physics are causally closed; there are no physical events that are not caused by other physical events. Were this not the case, then there would be, at the explanatory level of physics, miracles: physical events with no physical explanations. But [Page 517]if the instantiations of mental properties are causally efficacious with respect to the physical, if having some mental property is the cause of some behavior, for instance, then we are left with only three possibilities. First, there are physical events that are not physically caused, and so there are physical events without physical causes. Second, whatever the mental causes the physical also causes, and so behavior is causally overdetermined. Third, mental properties are identical to physical properties. The first option is the modern version of Descartes’ solution. The third is the modern version of materialism, what is commonly called “physicalism.” The second? Well, about that there is much contemporary debate, to which we will return.

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