In modern society and science, which considers physics to be the ideal science and the ultimate explainer of the world, it is not surprising that the metaphysical idea of physicalism—the idea that everything is fundamentally physical—has taken root. While it is the concurrent view, especially of scientists, it is continuously under fire for lacking explanation. In addition, the arguments favoring physicalism specifically are surprisingly weak, considering how ubiquitous it is in society.
What Is Physicalism?
Generally, physicalism says that everything is fundamentally physical. It is primarily discussed in the mind-body debate, as it is the last bastion where physical properties are consistently difficult to explain. In this context, physicalism is the idea that mental states are just brain states. How this operates varies depending on the physicalist’s stance.
Physicalism can be split into two core stances. One is strong monism, which is reductive physicalism, where everything is explainable by some fundamental, core physical substance. The alternative is non-reductive physicalism, typically evoking emergence or supervenience, taking mental properties to emerge from or supervene upon physical ones.
Supervenience, in this case, says that mental properties are seen as separate from physical and can be explained in terms of the mental, yet they are still dependent in some way on physical ones. At the most basic level, the world is still fundamentally physical. Mental properties cannot change without a change in physical changes. This view allows one to retain physicalism yet also acknowledge non-physical facts.
Both of these views still want to maintain the core tenet of modern physicalism, as put forth by David Papineau—that of physical closure, every physical effect has a sufficient physical cause. This means that when you trace the causal history of any physical effect—there is never any need to appeal to the non-physical. As the physical world is then complete, it is a closed system.
Arguments Against the Core Assumptions of Physicalism
Arguments precisely squared against physicalism largely come in three flavors. Arguments from first-person experience (referred to as ‘qualia’), intentionality, and arguments specifically against the core principle assumptions.
The arguments against its core principles are not established outside of philosophy, but they may be the strongest objections against physicalism as it equally affects both stances.
Physicalism lacks positive metaphysical arguments; it is instead typically argued in the negative sense against other alternatives like dualism and idealism. The strongest arbitrator for the belief in physicalism may be its parsimony – that is, it is the simplest explanation based on our scientific knowledge. Why assume extra substances when all we have observed appear to be physical and can be entirely explained by physical causes? However, it is doubtful if parsimony is enough.
The stronger argument for physicalism, causal closure, seems indispensable scientifically and has a strong foundation based on causal evidence. Yet, it depends on causal principles that are not set in stone. If those fall through, physicalism does not have much of a leg to stand on.
Qualia: Subjective Experience
The most typical and intuitive argument against physicalism is that of first-person experience or qualia. Nothing in physical states, like that of brain states, indicates experiences.
The most intuitive form of the argument comes from Thomas Nagel, who asks us to imagine what it is like to be a bat, to experience echolocation. Simply put, you can’t. We cannot even begin to comprehend what it feels like to echolocate, no matter how well we understand how it works or even imagine how it would work to be able to echolocate. Perhaps we could design an echolocation module and couple it with our brain to feel echolocation, but we still would never be able to understand what it feels like to be a bat.
A similar argument is Frank Jackson’s knowledge argument, which points out that it doesn’t matter what knowledge you have about the color red; you cannot predict or understand the experience of seeing red without actually having the visual experience of it.
Experience, then, is personal, indicating a fundamental difference between the physical and the mental. We can only obtain the former subjectively, never objectively. This is a problem for physicalism as it is difficult to envision how we would investigate first-person experience physically. Even if we correlate it to a neural state, would it give us any sort of explanation or indication of subjective experience or the nature of it?
Information or knowledge that is impossible to attain from a third-person perspective is troubling for a view that takes the objective physical matter to be all there is. Non-reductive physicalism has to accept that there is a gap, one that may be impossible to bridge.
Intentionality, Meaning and Representation
Another property that philosophers tend to hold is that mental states, compared to physical ones, have intentionality, that they are about something. They have content and direction, even for things that do not exist. It is a property that is difficult to reconcile with physicalism. How would a physical state have content about something it has never come into contact with? If this is a property that cannot be reduced to physical ones, it violates causal closure unless it is entirely epiphenomenal.
The same argument can be made for meaning, as it does not appear to be an objective physical property but a subjective one. A word’s meaning is only in relation to our subjective meaning of it; nothing in its physical properties relates to its meaning.
Intentionality and qualia are properties that we assign to mental states. They are difficult to reconcile with physical ones; they are irreducible mental properties.
Arguments Against Reductive Physicalism
These are the main arguments against reductive physicalism, which non-reductive physicalism tries to solve. Most take these properties to be real, yet we don’t know how they would be reconciled with physical states. If mental properties are irreducible from their higher level, physical reductionism fails outright.
Reductive physicalism has struggled to explain these mental properties purely physically outside of eliminative correlation, taking mental states to be physical. This is an unsatisfactory explanation if one takes these properties to exist and have an effect.
It is possible that the questions of the irreducibility of qualia and intentionality are ill-conceived. As mentioned by A.N. Whitehead, it might be a fallacy of misplaced concreteness to treat mental states as concrete objects. It would then rather be a problem of complex relations, which property we try to find in the fundamental physical property and not its relations, like finding wetness or surface tension in H2O molecules.
We could also see the mental as non-matter fundamental entities of their own, like fields or energy, which trouble reductive physicalism if one does not accept them as fundamentally physical. The big difference between these and the mental is that they clearly have physical cause and effect, while it is not clear that mental states do.
Without such a solution, under the completeness of physics, we are left with having to remove the cause and effect of mental states and properties, which is the stance of eliminative materialism. It takes the self to be illusory at best.
This leads us to perhaps the most pervasive argument against reductive physicalism: that of intuitiveness. We tend not to see the mental as something entirely designated by physical states. It seems obvious that mental states of pain cause behavioral changes. Giving up the intuition may even be impossible for us.
Arguments Against Non-Reductive Physicalism
The non-reductive stance instead has the problem of trying to define how mental properties affect physical ones yet still retain the fundamentalness of the physical. An attempt to do this is to allow different degrees of interaction between higher-level properties (mental) and lower-level ones (physical) or with other higher-level ones, interactions that are irreducible in some sense.
Strong downward causation means that mental properties emerge from physical ones and can then affect physical ones. An example would be if cells emergent from physical properties produced something not predictable from their physical local properties. Based on our history of physics, there is little reason to believe this to be possible. Eventually, most seemingly emergent effects can be reducible to the lower-level ones, though, in especially complex systems, ideas of emergence continue to be pervasive.
In weaker stances of downward causation, the higher-level properties do not have a causal effect on the lower level, yet they can affect them indirectly. An example is the capacity of a wheel to roll. Rolling affects the lower levels, yet there is nothing in the lower levels that constitutes rolling. Rolling is an irreducible property.
The problem for both downward causations is that if you assign this special function, in our case, the mental, to be irreducible to the physical, you run into problems with causal closure. Either this special property is not causal and thus does not have any physical effect, or it breaks causal closure.
Another solution is that mental properties operate in parallel or supervene upon the physical yet do not cause physical effects. It is then questionable why we would assume any mental properties at all, as they are causally redundant and overdetermined.
Crudely, it presently seems like the options available as a non-reductive physicalist are overdetermination, epiphenomenalism, or denying causal closure outside of reworking our idea of causality. None are that attractive to a monistic physicalist.
Physicalism: Unsteadily Steady
Outside of accepting the full-on eliminative reductive physicalism, physicalism struggles with simple and cohesive explanations of reality. Non-reductive physicalism – if we take on the completeness of physical causality – appears to have to take on the problems of either being overdetermined or denying causal closure under our current view of causality to prevent epiphenomenalism.
The current debate concerns whether overdetermination is actually a problem or if there are alternatives that can avoid it. One alternative is to attack the principle of causal closure or even our underlying causal principles that shape our view of nature.
Although it certainly may be used as an argument against physicalism, its core metaphysical assumptions, and support undermine the non-reductive view that most take to be the preferable alternative.
None of the arguments against it are strong enough to discredit it outright, but their persistence has sown the seeds of doubt. Based on the history of science and parsimony, physicalism is incredibly steady, but without it, it appears naked. Finding alternatives or trying to make reductive physicalism work has become a common pursuit in the philosophy of mind.
Bibliography
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MCGINN, C. (1989). Can We Solve the Mind–Body Problem? Mind, XCVIII(391), 349–366. https://doi.org/10.1093/mind/XCVIII.391.349
Papineau, D. (2001). The Rise of Physicalism. In C. Gillett & B. Loewer (Eds.), Physicalism and its Discontents (1st ed., pp. 3–36). Cambridge University Press. https://doi.org/10.1017/CBO9780511570797.002
Whitehead, A. N. (2010). Science and the modern world (7. paperback ed., [repr.]). Free Press.
