The case against physicalism

The case against physicalism

What is physicalism?

Physicalism is the view that everything real is ultimately something physical. A more traditional term often used interchangeably is materialism – the view that everything is matter – but this term is used less frequently now that we know forces such as gravity are not strictly material.

Physicalism does not deny that many things such as consciousness seem non-physical. But in the end physicalists usually claim such things supervene in some way on the physical, or can be reduced to physical entities. What does it mean to supervene? If you recall the old dot-matrix printers, think of how they printed pictures as a series of dots. The picture supervenes on the physical dots. If two pictures have an identical dot pattern, the pictures must be identical. Similarly, physicalism entails that apparently non-physical entities supervene on physical properties.

It should be noted that there are various physicalist views such as token and type physicalism, and reductive and non-reductive physicalism. There are also different conceptions on what it means for something to be physical (theory-based and object-based). These nuances can get very complicated, and won’t be explored here.

Physicalism and God

Given we normally conceive of God as non-physical, atheism is a consequence of physicalism. Physicalism also rules out substance dualism – the view that our minds or souls are made of a non-physical substance. It’s worth noting that there is a view known as Christian physicalism, which entails that there is no such thing as a non-physical mind, soul or spirit. Of course Christian physicalists are not true physicalists, as they admit the existence of God as a non-physical entity.

Why physicalism?

Why be a physicalist, when entities like minds seem obviously non-physical? According to Daniel Stoljar, “we live in an overwhelmingly physicalist or materialist intellectual culture. The result is that, as things currently stand, the standards of argumentation required to persuade someone of the truth of physicalism are much lower than the standards required to persuade someone of its negation” 1.

Physicalism is a view generally adopted by default. Few people go through the arguments for and against the view. As it turns out, the arguments in favour of physicalism are not very persuasive.

Argument from science

This argument is based on the success of science. Science has been extremely successful, and science has shown us that there is no non-physical stuff. So physicalism is true.

This is a dubious claim. Here’s an analogy by philosopher Edward Feser:

1. Metal detectors have had far greater success in finding coins and other metallic objects in more places than any other method has.
2. Therefore we have good reason to think that metal detectors can reveal to us everything that can be revealed about metallic objects.

This argument is fatally flawed. Metal detectors ignore shape, colour and other aspects of metallic objects and focus on their metallic composition. They don’t reveal everything about metallic objects.

Similarly, science is successful precisely because it focuses on aspects of nature that can be observed in some way, predicted and controlled. Non-material things are not as amenable to scientific investigation, but that doesn’t mean science has shown they don’t exist.

Argument from neuroscience

Doesn’t neuroscience show that the mind is nothing more than brain processes? This view was expressed in a famous essay by Tom Wolfe, Sorry, But Your Soul Just Died, reporting on the progress of neuroscience in 1996 2. Twenty years later, is that what we’ve concluded? No. Neuroscience doesn’t tell us how the brain works, or even conclusively which bit of the brain is responsible for each function.

Neuroscience uses brain imaging to investigate the workings of the brain. A common technique is functional magnetic resonance imaging (fMRI), and despite appearances fMRI images are not snapshots of the brain in action. fMRI doesn’t measure brain activity, but rather blood oxygen levels (BOLD) as a proxy for brain activity. This is poorly understood, and also has a 2-5 second delay and so isn’t concurrent with actual brain activity.

Importantly, fMRI images are not pictures of brain activity. They are statistical representations of a highly complex system. Each region interacts with
other regions and is part of many experiences. Seeing one area light up in response to a stimulus doesn’t necessarily mean a particular sensation is felt, and it doesn’t capture higher functions such as our sense of self, our intentions, and our voluntary actions.

Interpreting image data is also tricky, illustrated by the infamous dead salmon study. A salmon purchased from a store was shown photographs of people and asked to guess what the people were feeling. The researchers found that when the imaging data was analysed, a small part of the salmon’s brain showed activity in response to the photographs. This is the multiple comparisons problem – if you perform enough tests, at least some of them will return positive results, even if they are not real. Because fMRI scans divide the brain into 50,000 or more regions, they are very susceptible to this issue.

What do fMRI images tell us about the mind and the brain? Statistical flaws aside, they tell us that certain mental activities are usually correlated with increased blood flow to certain parts of the brain. We aren’t even sure exactly what increased blood flow is actually measuring – hopefully neuronal activity, although some researchers doubt this.

Raymond Tallis sums up our knowledge of the brain derived from neuroscience well: “The conclusion from (as we have seen, rather wobbly) correlations of bits of consciousness with bits of brain activity that the former is identical with the latter depends on several elementary errors, notably that correlation is causation and causation is identity and that necessary conditions are identical with sufficient conditions. As regards the latter, while it is obvious that a brain in good working order is a necessary condition of consciousness, it does not follow from this that it is a sufficient condition of consciousness or that its workings are identical with consciousness” 3 .

We are a long way from being able to demonstrate that the mind is nothing more than the brain, a necessary requirement for physicalism to be true.

Argument from causal closure

This argument relies on the principle of causal closure of the physical – that physical effects have only physical causes. If mental events cause physical events (e.g. wanting to raise your arm raises it), then mental events must either be physical or supervene on the physical (which is physicalism).

What is the status of the causal closure principle? It is an empirical thesis that has developed over time. It is not implied by physics, but is rather a metaphysical principle. Causal closure is widely accepted, but has no knockdown arguments in favour of it. After all, we don’t even really have a widely accepted theory of causality. And yet causal closure is one of the main argument for physicalism.

Causal closure also faces a number of problems, such as that of mental causation. If a mental event causes a physical event, there must be a physical cause of the event if causal closure is true. But does this mean the mental event is irrelevant? This is Kim’s exclusion argument, and a significant problem for non-reductive physicalism.

Another issue for causal closure (and thus physicalism) is Hempel’s dilemma. If we define physicalism by reference to contemporary physics, then it must be false — after all, who thinks that contemporary physics is complete or entirely correct? But if we define physicalism by reference to a future ideal physics, then the definition is meaningless — after all, who can predict what a future physics contains?

Issues for physicalism

As shown above, the arguments for physicalism are not particularly strong. But physicalism also faces a number of significant issues.


Our mental states are about things other than themselves – this is called intentionality. For example, consider ink on paper spelling the word “brain”. The ink shapes are meaningless until we give them meaning – the physical properties of the ink and the letters do not give them meaning. Our thoughts give them intentionality. But if physical neural processes are like physical ink marks, devoid of intentionality, how can thoughts (which have intentionality) be merely neural processes?

The “hard” problem of consciousness

According to David Chalmers (echoing Noam Chomsky), “the intentionality issue is a problem, but the qualia issue is a mystery” 4. What is it like to feel pain? What is it like to see the colour red? These are the properties of experience known as qualia, and they have a number of important characteristics.

Firstly, qualia are private, as they are experienced through the first person. Qualia are also ineffable – the experience of qualia cannot be fully conveyed through words. Finally, qualia are directly accessible through consciousness.

Physical objects don’t share these these properties, and so qualia are a problem for physicalism – there is an issue in explaining how physical properties give rise to the way things feel when they are experienced. This is known as the explanatory gap.

Can neuroscience correlate qualia and neural states? No, at best it can only correlate verbal reports of qualia with neural states. Qualia are private, so correlations could be consistent with qualia inversions (e.g. colour spectrum inversions).

There are a number of well-known arguments that demonstrate the difficulty qualia poses to physicalism. The best known is probably Jackson’s knowledge argument, which poses the following scenario:

Mary is a brilliant scientist specialising in the neurophysiology of vision. She knows all the physical facts about colour and perception. Mary has spent her life locked in a black and white room with a black and white monitor to view the world. When released from the room, and seeing red (say) for the first time ever, does she learn anything new?

Intuitively, yes. Mary’s experience of seeing red has taught her something new about how people see the world.The argument is outlined below:

1. Mary knows all the physical facts about colour vision.
2. Mary learns some new facts on leaving.
3. There are non-physical facts about colour vision, so physicalism is false.

There is clearly an issue for physicalism if the knowledge argument is sound. How do physicalists respond?

Primarily, they argue that Mary hasn’t really learnt anything new. Rather Mary has gained a new ability (or know-how), or she has obtained knowledge by acquaintance which she already knows.

Alternatively, some physicalists use a different definition of physicalism, or use a different definition of what it means to be physical. A more recent approach is to explain the apparent discrepancy in terms of phenomenal concepts.  The apparent gap between consciousness and the physical world is explained rather as a gap in our concepts of  consciousness and the physical world.

Frank Jackson himself no longer believes the knowledge problem is an issue for physicalism. He has adopted representationalism, holding that qualia are nothing more than intentional or representational mental contents. This reduces the hard problem of consciousness to the easier problem of intentionality.

Other responses to the explanatory gap include Dennett’s eliminativism. His belief is that our phenomenal features of the perceived world are not actually qualia, but only seem like qualia, and that there is no “hard problem” of consciousness. The Churchlands take eliminativism to the extreme and deny that qualia exist at all.

David Chalmers (who popularised philosophical zombies as another argument against physicalism) comprehensively argues that none of these strategies can sensibly close the explanatory gap 5. Instead, options reduce to either some form of dualism or consciousness somehow being a fundamental part of physical reality. An example of the latter is Galen Strawson’s panpsychism.

Epiphenomenalism is a form of dualism that holds that mental and physical properties are distinct, but mental properties have no causal powers. This denies mental causation, which is unacceptable to most people, and is incompatible with our knowledge of our own minds.

Historically, substance dualism (or Cartesian dualism) has been the most widely accepted solution. The explanatory gap is because the mental and the physical are different substances. Of course, if substance dualism is true, physicalism is false.

Substance dualism

Substance dualism is usually rejected out of hand as “outmoded”, or “implying magical substances”. How reasonable are the objections to substance dualism?

Given the rising popularity of forms of panpsychism, which implies all matter is conscious in some sense, accusations about magical substances seem rather misplaced. But what are the other objections to substance dualism?

Doesn’t neuroscience refute dualism?

No, we’ve seen that neuroscience does not demonstrate the mind is identical to the brain or brain processes. There are a small but significant number of neuroscientists who are dualists, such as Nobel Prize winner John Eccles, UCLA neuroscientist Jeffrey Schwartz, and Mario Beaureguard, author of The Spiritual Brain: A Neuroscientist’s Case for the Existence of the Soul.

Interestingly, it seems we are hard-wired in some way to be dualists,  even if we are neuroscientists who are physicalists. According to recent research, “although few neuroscientists openly endorse Cartesian dualism, careful reading reveals dualistic intuitions in prominent neuroscientific texts” .

The interaction problem

How does the immaterial mind interact with the material brain? Given dualism, there must be some kind of causal connection between the two entities, and currently we don’t have a viable explanation.

This is an issue for dualism, but it certainly is not a fatal objection. Newton didn’t have an answer to what the causal agent was for his gravitational force, which was inexplicably capable of acting at a distance. Arguably, we haven’t progressed much further – we explain the gravitational force in terms of hypothetical particles called gravitons that we have never observed and are unlikely to ever directly detect.

There are four fundamental forces we currently know of – the strong and weak nuclear forces, electromagnetism, and gravity. It seems possible that there is a fifth basic force associated with some kind of mental field. This isn’t far removed from panpsychist theories about consciousness being a fundamental part of nature.

Contemporary physics is also somewhat encouraging to the possibility of interactionism. Quantum mechanics altered the status of an observer to an active participant that affects a system’s behaviour. It is possible that consciousness plays a role – perhaps the defining feature of measurement is that it involves conscious observation. This is the essence of the Von Neumann–Wigner interpretation of quantum mechanics, where consciousness causes the collapse of the wave function. This is admittedly a fringe theory.

Causal closure (again)

We’ve mentioned causal closure previously, and it is closely related to the interaction problem. The principal of causal closure states that physical effects have only physical causes, which seems incompatible with substance dualism.

As explained earlier, causal closure is a metaphysical thesis rather than a law of physics, and it is by no means certain. If a fifth fundamental force does exist, or if consciousness is an important effect in quantum mechanics, then causal closure is false.

Dualism is still viable

Substance dualism is still a viable theory of consciousness, despite its relative unpopularity amongst philosophers. Lycan, a physicalist, nonetheless argues that “no convincing case has been against substance dualism, and that standard objections to it can be credibly answered”7. Dualism neatly resolves the problems of consciousness, and has as much support or more than physicalist alternatives.

Hylemorphic dualism

One dualistic alternative to substance dualism that has been gaining in acceptance amongst some philosophers, especially Thomists, is hylemorphic dualism, a view going back to Aristotle that regards being as a compound of matter and form. Form is the essence of a thing, what you might call its organising principle, and in hylemorphic dualism the human soul is regarded as the form of the body. A good defense of hylemorphic dualism by David Oderberg can be found here.


Although physicalism is the default view in our intellectual culture, the arguments for physicalism are not particularly strong, and there are some substantial arguments against it. It is equally intellectually respectable to hold to a dualistic view of reality.


Stoljar, D. (2001). Physicalism. [online] Available at: [Accessed 1 Jun. 2016]. 

2 Reprinted in Wolfe, T. (2000). Hooking up. New York: Farrar, Straus, and Giroux.

3 Tallis, R. (2009). Neurotrash | New Humanist. [online] Available at: [Accessed 1 Jun. 2016].

4 Chalmers, D., 1996, The Conscious Mind, New York: Oxford University Press, p24.

Chalmers, D. (2010). The character of consciousness. Oxford: Oxford University Press.

Mudrik, L. and Maoz, U. (2015). “Me & My Brain”: Exposing Neuroscience’s Closet Dualism. Journal of Cognitive Neuroscience, 27(2), pp.211-221.

Lycan, W. (2009). Giving Dualism its Due. Australasian Journal of Philosophy, 87(4), pp.551-563.