How to be a dualist

How to be a dualist

David Curtis

UCL Genetics Institute, University College London

Centre for Psychiatry, Queen Mary University of London


Is dualism really that bad?

One of my reasons for writing this is that people seem to think it’s not OK to be a dualist. There’s this notion that dualism is somehow a thoroughly disreputable position. People go “Ah but that’s dualist” or say “Cartesian dualism” as a euphemism for “nonsense”. What I’m going to claim here is that dualism is in fact intellectually quite respectable and defensible, as long as you do it right. Maybe you still won’t tell other people that you’re a dualist but at least you might feel a bit better about yourself.

Where to draw the line

Saying “mind-body dualism” is risky because the word “mind” is often used to refer to mental activities such as thinking, judging and remembering. It’s perfectly obvious that these are activities of the brain and if we start trying to split them off from the rest of biology we will rightly be shot down in flames. In the defensibly dualist view which we are promoting the only activity we will seek to separate off is the function of subjective conscious experience, involving qualia such as the experience of seeing the colour red. In this scenario, dualism offers a response to Chalmers’ “hard problem of consciousness” and says that the activity of having conscious experiences occurs outside of, or apart from, the physical universe (Chalmers, 2011). It might be easier if we referred to this as “consciousness” rather than “mind” but in fact many people seem to use the word “mind” to refer to the same thing so we will go along with that while at the same time emphasising that we do not intend to use mind as including mental contents or mental activity. Using this language, we’d better say with reference to “Cogito, ergo sum” that the subject of “Cogito” is the brain not the mind and that one can observe that there is a brain which is having thoughts and which refers to itself as “I”. But this thinking activity is not what we are referring to when we talk about mind, or consciousness, as being different from the body. Rather, mind can have a conscious experience of this thinking activity, as it can of other subjective experiences, but it doesn’t do the thinking. The dualism we’ll be talking about will be between the body and thinking brain on the one hand and the mind, or consciousness of subjective experience, on the other.

Think big

We’re going for substance dualism so let’s go all the way! Often one can read about people struggling with a non-physical mind as if consciousness is some weird stuff in the universe which we can’t see or measure. This is a very half-hearted approach. For proper substance dualism we need to say that there is a physical universe consisting of stuff with mass, energy and the other qualities of matter which exists in space and through time and which complies with all the laws of physics as we have come to discover them. Absolutely none of that needs to apply to consciousness. Not only are we talking about something which has no mass and no detectable effect on the material universe, we are talking about something which is not part of the physical universe, not necessarily located in three-dimensional space and for which even notions such as time, mathematics and logic may be completely inapplicable.

Dualism may be unscientific but it’s not anti-scientific

When people hear that dualism is unscientific they may take this to mean that it is not compatible with science. That there is an either-or choice. Either you accept science like other rational, enlightened people or you cling to the superstitious nonsense which is dualism. In fact, the term unscientific has a more technical meaning, which is that something is not amenable to study using the scientific method. One cannot construct hypotheses and test them with experiments. It is something which might be true or might not be true but as it seems that there is no way to gain any further useful information one way or the other it is not an appropriate subject for scientific investigation. Arguably, the hard problem of consciousness is now widely viewed as an unscientific question. It looks very much as though it will not be possible to carry out research which will throw light on the nature of consciousness and so neuroscientists are attending to more fruitful avenues. However to say that it is unscientific to propose that consciousness is different from the physical universe does not mean that such an idea is incompatible with science and a belief in science, just that the proposal does not seem to be capable of being investigated using scientific methods.

Actually, dualism is quite scientific

Although we don’t seem to hear about it much, for the last hundred years or so the basic understanding that scientists have about the nature of the universe in fact has a profoundly dualist feel to it. Orthodox quantum theory, as for example relayed by Stapp, has right at its heart the notion of an observer who has a conscious experience of the measurement of a physical event (Stapp, 2017). The nature and ramifications of this act of observation are subject to debate and speculation but there is no denying its centrality. Quantum theory does not seem to demand that the observing consciousness is non-physical but it certainly accords a special role for the observer which is qualitatively different from that of the physical events and measuring devices (which could include eyes and brains) which lead up to the act of observation.

While we’re mentioning quantum theory, the universe is not deterministic

There’s plenty of room for disagreement about the implications of quantum theory but one thing which seems absolutely clear is that the universe is not proceeding inexorably on a predetermined path which would in principle be predictable if we knew the position and velocity of every sub-atomic particle, including those in everybody’s brains. If we put Schrodinger’s grandchild’s cat in a box with a device that will kill it if a radioactive isotope emits a particle within a certain time frame then we have few things which we can argue about. We can argue whether the cat is both alive and dead till we open the box to take a look. We can argue whether the cat can act as an observer and knows perfectly well whether it is alive or not before we look. And we might argue that all the quantum uncertainty collapses when the particle hits the macroscopic measuring device (though apparently this is a bit left field). However one thing everybody seems to agree about is that the particle emission is a genuinely random process, its timing unknown and unknowable even in principle. So if anything ever happens in the universe which is contingent on a quantum event (and plenty does) then we can be very confident indeed that determinism can be discarded and is inconsistent with science.

Time for a silly analogy

At this point I’m going to introduce an analogy which will be helpful to illustrate various points. I’m going to talk about running a computer simulation of a three-dimensional world but please, please, please don’t think I’m for a moment moving towards the lame “we’re all living in a simulation” idea. It’s just an analogy, OK? Let’s consider a simulated world in which computer generated characters can move and interact. We could write the code to determine how they behave or if we have a bit more time and processing power we can write code to have them evolve or even to have a whole universe developing from a simulated big bang. Each part of this is all perfectly feasible and we can see real world examples of how fairly simple rules can allow computers to develop complex behaviour, such as playing go or chess. Alternatively, we can write explicit rules for artificial characters to move around in a virtual three-dimensional world and we can see this happening in any first-person shooter video game. These characters can carry out pretty much any desired range of behaviours. They can shoot at us, dodge, duck, sneak around behind us, issue feints, have aims and intentions, be cautious, be vengeful, whatever. We could program them to do science experiments or, taking a bit longer, we could set up the framework which will allow scientists to evolve by themselves.

So one thing we can do with this pitiful analogy is to get a better handle on the radical nature of substance dualism. As the simulation runs on the computer, the notion of “space” in this virtual world has absolutely nothing at all do with the space of the three-dimensional real world which the computer exists in. Simulated physicists within the virtual world could do all the experiments they liked and would still have no idea at all that the world they inhabited was actualised by electrons moving around silicon. Their notions of “down” and “up” would not have anything to do with any actual spatial displacements of electrons in the computer circuits. If the computer was set up with a monitor that allowed an external human observer to see from the vantage point of a virtual character, the virtual scientists could have no idea at all about the monitor LEDs emitting light, this travelling to the eyes of a human, eliciting brain activity and (mysteriously for us too) producing a visual experience in the observer.

The quality of conscious experience is unique and different

If we’re saying consciousness is different from the physical universe then we may want to ask, what is it like? A key insight which is absolutely mainstream science but which is a bit hard to get one’s head round the first time one comes across it is that absolutely all our experience of what we think of as the world is in fact an experience generated by our brains. The world as we see it does not exist. There is a world which exists and the world we see is a kind of representative model of it. But it is not a replica of it. We are not perceiving or experiencing the world, we are experiencing a brain-created representation of the world. To take a concrete example, we can consider our experience of seeing the colour red. We assume that the experience is a consequence of a particular pattern of neural activity in our brain, that there is a neural correlate of the conscious experience of seeing red. This activity may be provoked by any of a number of upstream events – light of a particular wavelength hitting the retina, an after-image, a hallucination, a dream. A key thing to grasp is that there is no “redness” anywhere else in the situation other than in our conscious perception. The neurons which are active are not red. The light hitting our retina, referred to by physicists as red light, is not in fact red but simply consists of electromagnetic radiation of a particular wavelength and the red object we perceive has no redness to it at all, simply having a surface which absorbs some wavelengths of light and reflects others.

This issue is so central and so challenging that it may be worth filling it out a bit. To help with this, it may be useful to realise that the information transmitted from our retinas to our brains is absolutely nothing like a photographic image. In fact, each neuron in the optic nerve, of which there are only around a million or so, transmits a little piece of information such as “vertical line”, “moving up fast”, “somewhat greenish”, “a corner, maybe”, “shimmery”, “bright point”, etc (Mitchell, 2018). The information is quite messy, with the activity of each neuron being probabilistically related to a given stimulus rather than there being strict one-to-one relationships. All this input gets processed by the brain to construct what it thinks the world is like and to produce this clear, high resolution, beautifully coloured, three dimensional model which we see when we open our eyes. But what we see is a colour-coded representation of an external world which in reality consists of nothing but particles interacting with electromagnetic radiation.

The nature of our consciousness is the nature of our subjective experiences and these experiences exist nowhere else. The quality of consciousness is the quality of our sensory perceptions but also our experiences of the other activities of our brains. Our experiences of sights, sounds, smells, thoughts, memories, emotions all constitute the fabric of consciousness and these experiences exist nowhere else. The external stimuli for sensory perceptions exist in the physical world and the neural substrate for them exists in the physical world but the world as we experience it exists only in the mind, or is the mind.

Dualism solves the hard problem

Going back to our simulated computer world analogy, if we plonk a human observer with amnestic syndrome in front of the screen we can offer a solution to the hard problem of consciousness. Amnestic syndrome means that one is completely unable to lay down any new memories and everything one knows is what one is informed of in the present. We can show our observer the viewpoint of a computer character, alongside the personal history of that character, and we can say that this is perfectly reasonable representation of the hard problem of consciousness. We have a subjective experience of what is happening in the computer world. The subjective experience, consisting of the human observer seeing colours and shapes representing that world, is completely different from the actual nature of the computer world. We can take one look at the setup and understand that it would be completely hopeless, from within the computer world, to understand how it was that there could be a conscious human observer in external space with eyes and neurons who could detect the electromagnetic radiation from a monitor which we did not even know existed. Nor could any experiments be done in the computer world which would throw any light on this issue. We could go home, comfortable simultaneously with the understanding that our physical world was in some way capable of being experienced by an observer and also with the realisation that there would never be any way to understand the nature of how this could be achieved. Hard problem solved.

How does neural activity translate into conscious experience?

We don’t know.

The mechanism whereby patterns of neuronal excitement translate into qualia remains completely obscure. Progress is being made towards identifying patterns of activity which distinguish conscious experiences from perceptions which are not conscious (Mashour et al., 2020). In animal studies it is becoming possible to identify specific neurons which seem to encode whether a crow thinks it has seen faint flash of light or not (Nieder et al., 2020). But one can envisage that even if we arrived at the situation of having fairly full knowledge about some neural correlates of conscious experience we would still face the same fundamentally difficult question. We could say that every time this particular set of neurons is activated, maybe with this pattern of activity over time, the subject experiences seeing a red flower. But we would still have to answer the same question, how? How do these little brain cells transmitting electrochemical signals to each other turn into my experience of seeing a red flower?

This question is really here as an opportunity to state clearly how neuronal activity is not translated into conscious experience, which is via electromagnetic signals from the brain. The idea that such signals could be helpful may have an initial superficial appeal. In the physical world, if we want to detect human brain activity then one way to do it is to measure the electrical signals generated when large numbers of neurons close to each other activate in a synchronised fashion. But the actual informational content of neuronal activity is encoded at a much, much more specific level, with the activity of sets of individual neurons, some close to each other and some distant. This can be visualised directly in animals with small brains such as mice and birds and one can stimulate individual neurons of people undergoing brain surgery. The basic activity of a neuron is not to conduct an electrical signal in the way that a wire does but to allow a series of ion channels to open and close in a way which results in metal ions moving in and out of the cell and this then produces fluctuations in the local electrical field. When this electrochemical action signal propagates to the end of the axon the ion flow across the cell membrane stimulates the release of neurotransmitter into synapses, thereby modifying the activity of other neurons. The gross electrical activity which can be picked up in experimental situations resembles the level of hubbub which may occur at different times and places in a cocktail party without capturing any detail of any individual words actually spoken. However the neural correlate of a conscious experience will necessarily involve specific patterns activation of individual neurons scattered across several cubic centimetres of brain. We need to remind ourselves of our dualist position and say that the fundamental mechanism of consciousness does not need to be constrained by being able to detect things such as fluctuations in an electromagnetic field but rather by the detection of a number of spatially scattered events. And that what gets detected may not relate to physical characteristics such as voltage but perhaps to something more nebulous such as a pattern of information. In any event, the original answer still stands. We don’t know.

Does consciousness do anything?

Substance dualism, in which conscious subjective experience is of a fundamentally different nature from the physical brain but can in some mysterious way be able to respond to brain activity offers an easy solution to the hard problem of consciousness but not a full solution. Difficulties arise when we begin to ask whether there is any reciprocal effect of consciousness on brain activity. The notion that an immaterial consciousness could impact the physical world is described as interactive dualism and has implications which may tend to curb our enthusiasm. First, though, let us begin by drawing strength from Chalmers’ aphorism: “There is some irony in the fact that philosophers reject interactionism on largely physical grounds (it is incompatible with physical theory), while physicists reject an interactionist interpretation of quantum mechanics on largely philosophical grounds (it is dualistic).”  (Chalmers, 2011)

Why might we think that consciousness “does something” to the physical universe? The first, and probably weakest, answer is that it feels as if it does. It feels as if we can carry out consciously intended actions. However there is room for considerable doubt that this is the case. Although the issue remains controversial, there is a respectable school of neuroscience which says that conscious intention is in fact illusory. For example, if we carry out brain scanning and ask a subject to at some point decide to lift their finger we may discover that the brain has actually already made the decision before the subject consciously does so. We can observe that thoughts arise undirected, that almost all our actions, even the most skilled ones, are done unconsciously and perhaps before we are aware of them. We can see that arguments about free will have raged for centuries with no satisfactory resolution. In short, it is hard to appeal to the experience of willed action as evidence that consciousness can have a physical effect.

Perhaps a stronger argument for interactionism comes from consideration of memory. We begin by observing that it looks very much as though consciousness itself does not have a capacity to remember things. There are neurological conditions which mean that somebody can have a conscious experience and subsequently, while remaining fully conscious, have no conscious recollection of it. Anaesthetists can give a patient medications which mean that although they might have conscious experience of a pain or discomfort they will be left with no memory of it. Since, in a dualist view, these conditions and medications affect the brain rather than consciousness itself it seems that we are forced to conclude that memory is a function of the brain and that anything consciousness knows about the past depends on the memories which the brain provides to it. As something of an aside, we can note that if consciousness has no memory then it seems we cannot be sure that the consciousness dealing with our experiences now is the same consciousness that was dealing with them a moment ago. If all our memory, including our identity, is stored in our brains then there seems no powerful argument to claim that an individual’s consciousness persists through time. All we know is the consciousness of this moment. As we have suggested before, it is not clear that time, as a property of the physical universe, has anything to do with consciousness at all. These are uncertainties which we shall leave unaddressed.

If we are looking for evidence that consciousness can impact the physical universe then we can note that we can remember subjective experiences, for example we can remember seeing something red. Now it is true that the memory of the perception is not the same as the perception itself but the memory does seem to capture some of the subjective qualities of what it is like to see something red. If the brain had relayed the experience to consciousness but consciousness had not replied then how could the brain have laid down in itself a memory of what the experience was like? And if the brain has acquired such a qualitative memory then it can only have done so by consciousness, in some way or another, exerting an effect on the brain. This seems to make quite a compelling case for interactionism. However, an alternative explanation might be that the neural activity which produces a conscious experience of a perception always simultaneously lays down an associated memory which, when activated, produces the conscious experience of the memory of the perception. If we do not find this explanation convincing then it seems we would be obliged to accept that consciousness can impact the brain. From a subjective point of view it does seem as if in general one can have conscious memories only of things which have been consciously perceived rather than of the myriads of sensory experiences which are not consciously perceived. On the other hand, this argument may be somewhat weakened by the fact that people can also remember things which have not happened, as experiments regarding witness reliability demonstrate, and this would seem to suggest that there is indeed a capacity to generate memories of subjective experiences purely from information about their substrates.

In fact, a more radical question can be asked about consciousness and memory. If consciousness has no memory, then how is that I am so sure the redness I experience now is the same as the redness I have always experienced in the past? Where does the knowledge of what redness is like reside? Are there some attributes which consciousness can store (what redness is like) while others are stored in the brain (the fact that I saw a red thing yesterday)? Or is it the brain which stores both?

Whether or not the brain can actually remember conscious experiences, it seems undeniable that the brain knows about consciousness. This would not be the case if consciousness were a purely passive observer of brain activities. In that situation, brains could go through their lives pursuing their owners’ purposes and helping keep their owners alive without have the slightest inkling that their activity was giving rise to conscious experiences. (In our computer world analogy, this would correspond to having a human observer being able to see the simulated world from the viewpoint of a virtual character but having no influence at all on that character’s actions.)  Instead, we have the situation where brains are thinking, talking and writing about experiences being subjectively experienced. It seems very difficult to think how brains could know that conscious experience happens if consciousness had no physical effects at all on brains. From this point of view, we can argue that the existence of this discussion that I am writing and you are reading is proof that consciousness can produce consequences in the physical world.

And one final argument in favour of interactionism comes from the perspective of evolution. It looks very much as if the brain has a function, among others, to organise information in a way such that it can be experienced by consciousness. An alternative view is that there is something intrinsic to what would be the natural activity of the brain which provides the neural correlates of consciousness and that brains would behave exactly the same way whether they gave rise to conscious experiences or not. If we find this implausible and think that on balance it seems likely that the brain does indeed represent a very sophisticated device for doing whatever it takes to produce phenomena which can be experienced by consciousness then we have to conclude that this ability has evolved. It does not just happen to be there. But for a function to evolve then it has to affect the fitness of the organism. We have to say that in some way being conscious provides some degree of survival advantage. But this can only be the case if consciousness has actual effects.

If consciousness does something, what does it do?

Although there seems to be a reasonable case that consciousness can have effects on the physical universe, the nature of what these effects might be is very unclear. The quantum uncertainty around the unfolding of physical events means that the ability of consciousness to have effects is not ruled out. It is possible to claim that aspects of neuronal activity occur at such a microscopic level that quantum effects are relevant while Stapp is very insistent that such uncertainty can apply at the level of the whole brain (Stapp, 2017). From this, settling on chocolate or vanilla might represent two alternate possible outcomes described probabilistically with a decision being settled by a quantum collapse (Chalmers & McQueen, 2020). To accept this as an explanation for how free will might operate would involve having a convincing proposal as to how consciousness might influence this process. Which I have not yet seen.

A problem with the idea of consciousness taking advantage of quantum indeterminacy to make choices is that it is hard to see how consciousness could have the slightest idea of which individual neurons it needed to activate in order to achieve a desired effect. A slightly more feasible notion might be that consciousness could impose a “vision” of a desired outcome which could be communicated to the brain and that once the brain was aware of this vision then it could work to achieve it. An attractive feature of this is that there might be quite a similarity between the vision of the desired outcome and the kind of perception which is meaningful to consciousness. For example, when I raise my hand there can be a subjective awareness of what it is like to have a raised hand. If my consciousness could communicate to my brain the awareness of having a raised hand as a desired result then my brain could set about raising my hand to achieve it. Then we could say that if consciousness “knows” what the pattern of neuronal activity corresponding to the experience of raised hand looks like then it therefore “knows” what pattern of activity to impose on the brain as a vision of a raised hand. An unattractive feature of this proposition is that involves consciousness imposing a particular pattern of neural activity across the brain which would be well downstream of the quantum uncertainties of individual neurons and which would seem to involve either quantum effects at a macroscopic scale or else the imposition of a set of molecular events which locally propagated back in time to the set of quantum events which would result in them. (These two conceptions possibly being equivalent.)

A more modest claim for a role of consciousness might be that it is able to report back something about the nature of the subjective experience. We can start with the perception of pain. It seems fairly obvious that a primitive organism could function perfectly well with mechanisms which detected noxious stimuli and triggered behaviours to avoid them. Human beings have spinal reflexes which will cause limbs to move away from sources of pain without any involvement of the brain. So what does conscious awareness of pain add? How does it help? One might think that the brain would be well able to come up with a perfectly acceptable response to pain without needing to be told by consciousness that it is really, really unpleasant. Does the conscious experience somehow add to the urgency and intensity of sensations which enhances evolutionary fitness? How would an organism that had conscious experiences be different from one that did not? Might it be that the effect of consciousness on the brain was to provide some additional input about the aesthetic quality of the experience? The extent to which something is pleasurable or painful? Beautiful or ugly? Fun or dull? Clearly much of these qualities could be assessed by the brain but does consciousness add some extra edge?

Maybe it would be possible to come up with a more satisfactory solution if we moved away from the ideas that the brain produces a neural correlate of qualia which are then consciously experienced and that there is also some way in which consciousness can impact on brain functioning. Maybe a more fruitful approach would be to consider experiencing as some kind of collaborative exercise between brain and consciousness. We could imagine that the two of them worked together with the brain providing the necessary information about the object of experience while consciousness, in becoming aware of it, provided a qualitative picture to the brain of what the subjective experience was like.

So there we go then

That’s about it. I don’t have answers to these questions but I just want to point out that it is not totally na├»ve, insane and hilarious to entertain dualism in the 21st century. The dualist position raises new problems which seem to require interactionism as a response and then things become challenging in different ways. But I don’t think it would be fair to say that our current understanding of the state of things renders dualism intrinsically ridiculous.


Further reading

Chalmers, D. J. (2011). The Character of Consciousness. In The Character of Consciousness. Oxford University Press.

Chalmers, D. J., & McQueen, K. J. (2020). Consciousness and the Collapse of the Wave Function. In S. Gao (Ed.), Consciousness and Quantum Mechanics (forthcoming). Oxford University Press.

Mashour, G. A., Roelfsema, P., Changeux, J. P., & Dehaene, S. (2020). Conscious Processing and the Global Neuronal Workspace Hypothesis. In Neuron (Vol. 105, Issue 5, pp. 776–798). Cell Press.

Mitchell, K. (2018). Innate: How the Wiring of Our Brains Shapes Who We Are. Princeton University Press.

Nieder, A., Wagener, L., & Rinnert, P. (2020). A neural correlate of sensory consciousness in a corvid bird. Science, 369(6511), 1626–1629.

Stapp, H. P. (2017).  Quantum Theory and Free Will: How Mental Intentions Translate into Bodily Actions. Springer.



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