A Causal Argument for Physicalism

A Causal Argument for Physicalism

Good arguments have been given to show that mental states are not reducible to physical states of the brain (neural transmissions etc.); and intuitively they don’t seem like brain states. Thus, some degree of dualism obtains, of one sort or another. But no one ever argues that mental causation is, or must be, non-physical. It is commonly assumed that all the causal machinery of the mind resides in the brain—in the physical correlates of the mind. Three kinds of mental causation can be distinguished: input psychophysical, output psychophysical, and intra-psychological—for example, perception, action, and perception-cognition (seeing causing a belief, say). The picture we have is that the correlated brain states causally act in such a way that certain effects are triggered, mental or physical. We don’t need to invoke a special type of causation to explain mental causation. If Cartesian dualism were true, we would presumably need to, since the mind could have causal powers without being accompanied by a brain. But most theorists today accept that the brain is the causal powerhouse of the mind. Mental causation is identical to brain causation: we can have an identity theory of it. There is no such thing as irreducibly mental causation—though there may be irreducibly mental properties or states or events or stuff. The case is like certain other characteristics of the mind: location, duration. In so far as mental occurrences have a location, it surely coincides with the location of the brain; there is no other type of location that the mental might have (the big toe, somewhere ten miles from the brain). Evidently, mental occurrences have a date and a duration: the pain or thought occurred at a specific time on a certain day, or took up a certain amount of time (the pain went on for ten minutes, say). Surely, these temporal coordinates coincide with those of the correlated brain processes; they don’t operate autonomously. If you know the timing of the correlates, you know the timing of the mental occurrences. We entertain no notion of irreducibly mental time: mental time is physical time. Mental causation thus acts in the same way—it comes down to physical causation. The place, time, and causal power of a mental occurrence are nothing other than those of the correlated brain occurrence. That doesn’t mean that all the properties of the mental occurrence are so reducible, but those three are; to that extent at least physicalism holds sway. In particular, causal physicalism seems true and is generally accepted.[1]

But the resulting position is uncomfortable, because it is hard to see how a more far-reaching physicalism could fail to be true also. How could it be that mental causation is completely physical while the causative factors are not themselves completely physical? That would mean that the causes and effects have properties over and above their causal profile. How could a mental cause not be physical if its causal powers are completely physical? The only way out is to embrace epiphenomenalism, but we are assuming that mental causation is real. If mental causation is real and reduces to physical causation, how can the mental event not be physical? If biological causes in the body operate by virtue of physical causation, aren’t they thereby physical—constitutively so? And we know they are: they are composed of chemical and physical stuff. So, the same thing must be true of mental causes: they must be made of the stuff that constitutes their causal machinery. How can the mind not be the body if its causal machinery is completely bodily? It would be different if the mind could act causally without a brain, but we are ruling that out. Causal physicalism thus entails ontological physicalism. The correlation can’t be mere correlation. If it were, and mental causation is real, we would have to say that the causal machinery is not completely physical; but it is, so the relation has to be more than mere correlation. The nature of the mental state must reduce to its causal nature, which is physical. Mental causes can’t be non-physical if mental causation is physical.

We could conclude from this argument that classic physicalist reductionism must be true, despite the cogency of arguments against it, or we could revise our view of physical causation as it occurs in the brain. That is, we could propose that the cerebral causal machinery is not classically physical: it isn’t just electro-chemical transmissions, or they are not purely physical as we currently understand the physical. Here panpsychism, or some variant of it, beckons: hidden in the brain there are properties or processes that go beyond what we habitually attribute to the brain—and these figure in the causal machinery on which mental causation depends. The mind as we know will then be reducible to these unknown properties. This is not physicalism in any recognized sense (or even pansychism); it is rather a doctrine with no name or currently-intelligible content. It might be called “Whatever-ism”: the mind reduces to whatever is in the brain that goes beyond what we now know of the brain and functions as part of the machinery of mental causation. At any rate, we have a puzzle here with no easy solution—the puzzle of mental causation. How can the mind not be physical if its causal machinery is physical?[2]

[1] When a sensation of pain causes a withdrawal of the hand, say, the causal mechanism consists in the fact that the neural correlate of pain initiates a sequence of neural impulses that culminate in the contraction of certain muscles. It isn’t brute and immediate, or strangely immaterial; the causal process is straightforwardly material—the brain doing what brains do. The causal relation is a physical relation.

[2] I think this has always been a prime motivation for mind-brain identity theories, though I have not seen it stated explicitly (though ideas close to it have been). Once you discover that the brain does all the work of moving things around in the mind you wonder how the mind can be anything but the brain; the only question is the design specifications of the brain machinery. We certainly know a lot about these specifications, but do we know everything about them?