One of the biggest arguments against substance dualism is the fact that when the brain is damaged, the mind is altered. If the brain and mind are two different substances, the mind should not be effected by brain damaged. But it is...

What are some solutions to this problem for substance dualism? Interactionism? Dual aspect monism?

  • How do we really know this? Medical literature abounds with stories of people in comas who, after recovering, reported that they were aware of everything that was going on around them? HOW DO YOU KNOW the mind is altered? You can't know what's in someone else's mind! That's the whole point.
    – user4894
    Commented Nov 4, 2018 at 21:08
  • I think medical literature also abounds with stories of people incapacitated to various degrees by traumatic brain injuries... Commented Nov 5, 2018 at 1:19
  • @user4894 Generally, when people’s brain are affected, their minds are affected, no matter what the causes are. And we can tell this by neurological examinations and other neurophysiologic testings. For example, when people get cerebral concussion, cerebral infarction, or encephalitis; or consume mind-bending drugs, sedatives, or stimulants; or have a brain tumor or degenerative diseases destroying their brains, their minds are altered accordingly, and this can be clearly examined or tested. Even you can tell this if you have a chance to see or talk with people in these conditions.
    – user287279
    Commented Nov 5, 2018 at 5:14
  • We have patients who seem to be in coma but actually aren’t. It’s explicable neurologically. The brain portion that functions to create consciousness is still working but those brain portions that function to manifest the signs of being conscious aren’t, such as locked-in syndrome, akinetic mutism, malingering cases, etc. These are infrequent cases and are not evidence that the mind is not dependent on the brain.
    – user287279
    Commented Nov 5, 2018 at 5:26
  • The only solution is non-dualism. All the rest are some form of dualism in disguise.
    – user20253
    Commented Nov 5, 2018 at 14:14

6 Answers 6


This is an important question, and one that interactive dualists are generally poor at even admitting exists. Most of the other physicalist attacks on interactive dualism are based on reasoning or science errors (asserting different types of things cannot interact is -- simply untrue; asserting science has shown energy conservation and causal closure of the physical are facts is likewise untrue, as shown by the current open nature of physics and continual discovery of new interactions, and by the spontaneous symmetry breaking in the gauge symmetry assumption). Defenses of dualism tend to focus on these refutable objections, and on the evidence in favor of dualism. Three good examples are The Self And its Brain, by Popper and Eccles, or this link, for a more recent example: http://www.newdualism.org/papers/R.Bernier/Bernier_Thesis.pdf

The issue for dualists should be made clear. Substance typically assume that consciousness is spiritual, and it interacts with the brain the way a TV broadcast station interacts with a television screen, or the way a remote drone operator interacts with a drone. This model accounts for some effect on consciousness from brain damage. If a TV's circuitry has a few wiring shorts, then it can malfunction in how it manifests a signal (such as a person knows what they want to say, but they are unable to form the words due to a stroke), and damage to telemetry sensors or camera on the drone can degrade the info getting back to the operator (stroke in optical processing of brain leads to blindness). Plus, dualists are often trying to defend a religious view in which "souls" are indivisible, hence they assert a an intrinsic indivisibility to consciousness. An example of both assumptions, from a recent dualist paper is here: http://www.newdualism.org/papers/R.Collins/Collins-Scientific%20Case%20for%20Soul.pdf Eccles model of interaction is more explicit, and has the same features.

The problem for both assumptions is that there has been considerable evidence for an extended time that CONSCIOUSNESS is affected by brain damage, and that we can lose bits of consciousness, not just our data or expression. The first documented case was a railway worker whose brain was penetrated by a spike in the 1800s, and underwent a personality change: https://www.smithsonianmag.com/history/phineas-gage-neurosciences-most-famous-patient-11390067/ A more recent set of examples is documented in "the Man Who Mistook His Wife for a Hat", documenting the case studies of a neurologist's patients, and the bits of consciousness they lost. Patients unable to even think of the left hand field of view, patients who cannot think about action verbs -- these are degradations of the DRONE OPERATOR, not of the data, or of the communication, or the drone behavior.

I have found only two dualist authors who admit this problem. Beloff http://www.newdualism.org/sites/moebius.psy.ed.ac.uk-dualism/papers/brains.html, agrees this observation supports physicalism, but he does not offer a solution. May and May offer a two-mode ad hoc addendum to dualism -- when enbodied, mind for TBD reasons tracks with bodies, but then when separate they don't: https://www.selfconsciousmind.com/TheoryOfMindAndBrain-12052011.pdf. May and May don't offer any rationale why, if minds can process "left side of visual field" when discarnate and there is no brain to process any of this in parallel, but then when there is a brain doing some of this processing, the mind can not then do the left side of visual field even if that portion of the brian is damaged -- they lack any explanation, other than "this is how it is".

Note, the damage/thinking correlation is not a fatal objection to dualism, but only to the two assumptions I noted above. A dualist model, to be compatible with this data, needs to allow that souls use brains to expand their functions and throughput of consciousness. This can be done with a much more complex, coupled/interactive model. Anyone who has driven the safety-assist cars which partially process the road data for you, then try to assist in controlling the car, will have experienced some aspects of an offboard thinking assist. Our cars do not couple directly into awareness, but per interactive dualism, our brains do. Hence apply this concept to actual awareness, and a dualist model that treats the brain as a shared enabler of some features of consciousness would be consistent with this data.

What this model would predict is that disembodied souls would have less capability and throughput than they do when embodied, and could also have different personalities. This is a consequence that most dualists are reluctant to accept, but this is only a problem for some models of dualism, and the wishes of dualists, not for dualism in principle.

Dual aspect monism (DAM) is refuted by all the refutations of identity theories, AND faces both the same problem dualists do, but also faces additional logic problems (the matter of the brain is still there, why would a wiring difference cause mental changes). I have not seen dual aspect monists even put the effort out that dualists have to articulate even as coherent a model as the TV/drone model. You will need another poster to come up with any DAM answers -- I don't think they have them.

  • This is a great answer. You have shown in extensive detail why interactionist substance dualism is proven wrong!
    – Noah
    Commented Nov 6, 2018 at 19:41
  • 1
    The reason philosophy of mind is still a very active field is because every effort to explain mind has some major problems. As these problems for interactionist dualism can be solved by a) narrowing the theory, rejecting some popular variants of it, and b) adding more complexity to it -- these problems are not fatal for interative dualism. I-D is actually in better shape than any other theory of mind I have found -- as the others either cannot be patched, or the patches appear to involve incoherence. I am an interative dualist ;-).
    – Dcleve
    Commented Nov 6, 2018 at 20:02
  • Thanks for the clear Dcleve. 10/10 answer!
    – Noah
    Commented Nov 7, 2018 at 0:04
  • my new question is related to this one
    – Noah
    Commented Nov 24, 2018 at 16:47

Descartes didn't think the organic functioning of the brain was irrelevant to our mental experiences. He drew a strict distinction between mind/soul and spirit, which he identified with the action of the nerves. Spiritual/nervous activity was, in Descartes' theory, a physiological movement that directly mediated the content of perceptions (and so on) into the pineal gland.

If you want the details, you'll have to read Passions of the Soul. But suffice to say that Descartes is very actively engaged with the idea that certain sorts of illusions and vices arise, not from either the external world or the mind itself, but from the improper organization of the physical mechanism of the brain.


If the mind is expressed on the physical 'plane' by means of the brain. Then a damaged brain would not express the mind faithfully. It follows that the mind can be unaltered by brain damage.

Conversely, if the mind is informed of the physical through the brain, a damaged brain would render a distorted view. Thus the mind's actions cannot be taken to pertain to the actual physical plane.

Thus we must conclude a damaged brain can not be seen as a reliable source of information about the non-physical mind. Furthermore assuming that the aberrant behavior of a brain damaged individual, in physical substance, is determined by an aberrant mind, as non-Physical substance, is not valid. So this argument against substance dualism is assuming the conclusion in its own proof.


Clearly when our eyes are damaged, our phenomenal experiences change; nothing seems especially problematic about this to substance dualism. From psychology and neuroscience (and lots of interesting optical illusions) we now understand that even our visual phenomenal experiences correspond not directly to the nerve impulses from the retinas, but are rather the result of significant processing by the brain. So, we would similarly expect brain damage to have the potential to change our visual phenomenal experiences.

The substance dualist could hold that the eyes and brain are just (somehow) providing input to mind / causally involved in our phenomenal experiences, and that the mind is different from the brain in a way not unlike the way in which mind is different from the eyes.


In Giving Dualism its Due, William Lycan (a physicalist) considers several objections against Cartesian Interactionist Dualism, and several arguments in favor of physicalism. He argues that the arguments in favor of physicalism are no worse than the arguments in favor physicalism, and the arguments against interactionist dualism are no better than the arguments against physicalism.

He characterizes this particular objection, the "neural dependence" objection, with a quote from Paul Churchland (Matter and Consciousness, 1984):

If there really is a distinct entity in which reasoning, emotion, and consciousness take place, and if that entity is dependent on the brain for nothing more than sensory experiences as input and volitional executions as output, then one would expect reason, emotion, and consciousness to be relatively invulnerable to direct control or pathology by manipulation or damage to the brain. But in fact the exact opposite is true . . . .

Lycan responds:

Of course the opposite is true. But why would any dualist accept the premise’s second conjoined antecedent? What dualist ever said, or even implied, that the mind is dependent on the brain for nothing more than sensory experiences as input and volitional executions as output? Descartes himself knew very well that the mental depended in a detailed way upon the brain. And the transducer explanation applies here as well. We may even add that cognition may interdepend in a close way with brain activity: there is no reason to suppose that the mind can do complicated reasoning without the aid of a physical calculator; in the real world, most people cannot do complicated reasoning without the aid of a physical calculator. Mind–brain interaction may be constant and very intimate. (Here again, the picture is implausible, but only because dualism and Cartesian interaction are implausible in the first place. Subtract those two implausibilities, and the rest of the picture is not bad at all.)

Earlier in the same article Lycan argues that both dualism and Cartesian interaction are indeed plausible (or at least approximately as plausible as physicalism is).


if you treat the brain (and to a lesser extent, cardiac nerves and one form of gut nerves) as an interface between mind and the physical, many things fall into place.

damage to the physical interface will render both sensation and response defective without any direct impact on the mind.

using the model of your mind as a drone operator — drone fitted with cameras, microphone, loudspeaker — odd behaviour of the drone is not the same thing as a damaged mind. the drone may be damaged, or communication may be damaged (for example, the screen the operator is using to sense things from the drone’s PoV may have failed), and this says nothing at all about the operator (your mind).

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