• Presumably the end game of dualist philosophers is to definitively prove the existence of ontologically separate mental states which cannot be reduced to brain states. If they succeed in doing so, then we would be able to make testable and falsifiable statements about mental states.
  • When materialists (physicalists) speak of matter in the context of the mind-body problem, they don't mean matter per se, as understood in physics. Materialist already accept theories which have multiple categories of basic substances (matter, energy, electricity, force, genes, etc...). In the context of the mind-body problem, what materialists mean by matter is anything that can be explained by empirical sciences.

But then, if dualists do achieve their goal, whatever proofs they provide regarding mental states will allow them to provide empirical theories with predictive explanatory power w/r to these mental states, and then these theories would become part of the empirical sciences, and hence part of the materialist world view.

As an example, if David Chalmers' theory of sensation being a fundamental quantity/variable in nature (as a way of explaining qualia) is true, then that would just mean there was a paradigm shift in physics, and any theory about the mind substance would be part of a physicalist world view. Dualism would also become indistinguishable from functionalism and none reductive materialism.

My questions:

  1. How could dualists definitively prove the ontological uniqueness of mental states without these states becoming part of the domain of empirical sciences?
  2. Can Dualism ever be distinguished from none reductive materialism?

4 Answers 4


The line is typically drawn slightly differently, mostly because the word "explain" is not precise enough for a hard-edged debate on the topic. As given in the introduction to Phyiscalism on wikipedia:

A "physical property", in this context, may be a metaphysical or logical combination of properties which are physical in the ordinary sense. It is common to express the notion of "metaphysical or logical combination of properties" using the notion of supervenience: A property A is said to supervene on a property B if any change in A necessarily implies a change in B.

Supervenience of the mental onto material implies that all changes in "mental state" can be fully grounded in some physical principle (I believe it is generally what you intended when you phrased the question in the first place, this is just the precise word). If a dualist was to somehow prove that there was a mental state which did not supervene onto a physical state, they would have proven dualism. At such a point, the mental state would not become material, because it would still not behave according to physical laws (in particular, it would exhibit mental behaviors such as freewill).

As for the "proof" of dualism or physicalism, the debate has raged for a very long time, and the general consensus is that nothing resembling proof can be acquired without dying (and it is generally presumed to be very difficult to bring such information back to share with the rest of us). Until we know "all of physics," the unknown is still out there. Those that do believe there is proof typically use the word "proof" in a way that permits their belief to shine through, such as a "scientific proof" or a "religious proof." In particular, the question of what does it mean to perceive something continues to divide the camps in a way that is so difficult that even the idealists, who believe there is only mind and matter is an illusion, can make a play. The challenge of empirically testing theories involving chaotic systems doesn't make the debate any simpler.

Finally, there's the question of randomness in empirical studies. If you really dig into statistics, there is no way to tell if some experimental results are a random distribution or a non-random (mindful) distribution. All you can do is look at the data and say how likely or unlikely that distribution was to arise by random chance. There is (intentionally) no way in statistics to be 100% certain that a variable fits a given distribution or not.

  • Could there be a "negative proof" in the manner Godel or Kant? If we take successful AI, whatever that means, to be the ultimate proof that mentality is physically grounded, would a proof that computing can never reproduce "that which" creates, maintains, and reproduces computing constitute a proof? It would simply be a proof that "something thought of" remains always irreducible to any possible representation of thinking. I suspect this may be a very naive idea already thoroughly refuted. Oct 30, 2015 at 15:06
  • I wont say its impossible, because very smart folk have found very clever negative proofs before. Personally, I have my own opinions based on my research suggesting there are physical situations which do indeed arise involving self-similar chaotic systems where it is impossible to prove no "mind" exists, due to the limitations of perception because we are inside the system, not outside of it. These "solutions" are forbidden by ZFC, as they form infinite descending sets when you model them, so they must not be physical (or at least not definable with sets or numbers), but with ZFC...
    – Cort Ammon
    Oct 30, 2015 at 17:44
  • 1
    ... you can construct something finite that is arbitrarily close to being called a "mind," so much so that limits in our measurements would simply overlook it. The existence of such minds could be true (indicating that the world is not totally modeled by set theory), or it could be false (indicating that the world is indeed all physical), but to the best of my understanding, the truth value of the existence of minds is not one which can be captured by empirical study by finite beings.
    – Cort Ammon
    Oct 30, 2015 at 17:48
  • @NelsonAlexander (tagging you now that I'm done writing). There's also the fascinating constructions Dan Willard is constructing, which build up the system of numbers differently than we usually do. His work constructs systems which are self-provable, defying Godel, simply by not making multiplication a total function, and in the process refusing the diagonalization lemma. Some of these worlds have fascinating properties which indicate there are things we can never know. One of them is that it is possible to construct sets whose cardinality is provably countably infinite, but...
    – Cort Ammon
    Oct 30, 2015 at 17:51
  • 1
    A key question for me for arguing why it makes sense to allow blurring: What am I: mind or matter? If I am nothing but matter, then I am duplicatable, have no mind, no control over my purpose, and no freewill. If am nothing but mind, then how do I affect the natural world? If I am dissatisfied with either extreme, and am more comfortable with compromise concepts like "the mind controls the body," to me that suggests I should explore directions which allow objects if interest to have both mental and material properties.
    – Cort Ammon
    Oct 30, 2015 at 20:14

These questions remain interesting, but I can't see that "dualism" is being adequately defined here.

As you yourself imply, the whole idea that dualists could "prove" the existence of the res cogitans or some "cognitive field theory" and then subject it to empirical testing is not, by definition, dualism. Your question is all contained within a naturalistic monism from the very beginning.

I am not sure how "dualism" is best defined today, but I suspect there are many "hard" and "soft" versions. We could imagine Leibnizian monads all operating independently. Or Cartesian substances. Or some "dark energy" wholly irreconcilable to any possible description of the universe. Or systems that operate randomly relative to each other. Perhaps the best case today would be matter subject to "entropy" versus matter subject to "life," even as we seem to be filling in the chemical and logical steps between.

But by any "hard" definition I would think dualism entails precisely that which cannot be reduced, converted, or proven. Everything "whereof one cannot speak," as Wittgenstein puts it. It is precisely that aspect of "mind" that remains in surplus, over and above whatever mind is able to observe and reduce pertaining to itself.

The very quality of irreducibility. The mind conceived of as a relentless "unlimiting" of whatever "limits" it formulates into natural laws or perhaps even logical principles.

So the question becomes: Is this Lockean "I know not what" or Kantian "ding an sich" simply extraneous metaphysical fluff? If we can't see it, chew it, or talk about it, why not just Occamize it? That may be a perfectly good answer from any scientific point of view.

I take Kant to be a paradigmatic modern dualist. And many find no good reason for his retention of the noumenal. It is, indeed, very unsatisfactory. As Fichte, Hegel, and others pointed out, by positing it, Kant appears to have already brought it under concepts and into his apparatus. He is blithely chattering on about the unspeakable.

My own sense is that Kant's critical philosophy requires it for a completion of the reasoning, free, moral subject. That which endows us with moral sense or higher purpose and prevents "reason" from ever being reduced to computing, not matter how powerful. In addition, Kant argues that we can "think" certain things we can never "know," let alone prove. And in this sense perhaps his "noumena" act like a zero in mathematics, as a kind of necessary placeholder between "one" and its "opposite."

So the "proof" of dualism would be a negative, a priori, Godel-type demonstration that "computing" of any sort can never reduce and reproduce that which creates and sustains computing. Or, if it does, then we have indeed become a whirling Hegelian Geist. The great thing about AI is that it really does bring these old questions back in an interesting, tangible way. The instinctive dualist looks suspiciously at AI and tries to grasp: What is it that we are really doing here?

  • This definitively answers question 1). Thanks. But it makes 2) even more puzzling. Oct 30, 2015 at 17:18

Presumably, different dualists have different end games, although I imagine most of them will agree to proving ontologically distinct mental states as goal. But I also imagine most of them will reject reduction of mental states to empirical experience, at least as understood by most materialists. If they thought that possible we would not be talking about philosophical zombies, which are defined to be empirically equivalent to humans, but without the mental states. Indeed, we can hardly expect dualists to go further than token identity non-reductive materialists, who already reject reduction of mental to physical, which for them contains empirical. No law relates mental to physical, says Davidson, there is something special in biochemistry that conjures up qualia, which are inaccessible by empirical means, says Searle.

I also think many materialists would take an issue with not meaning matter as understood in physics, and reject the talk about "substances". They are monists after all, there is one matter of which physics, chemistry, biology, etc. describe different manifestations.

It is probably close to the truth that dualism and non-reductive materialism are essentially equivalent empirically, although the practitioners of both will likely resist the thesis. Regardless, the distinction would survive it. That is because most dualists, like idealists, existensialists, etc., believe in a non-empirical aspect of reality, and our special (possibly private) access to it over and above the senses. Descartes had rational intuition, Kant had practical reason, Hegel had determinations of thought, Husserl and Bergson had phenomenological intuition, Heidegger had phenomenological insight, Chalmers writes "physical realization is the most common way to think about information embedded in the world, but it is not the only way information can be found. We can also find information realized in our phenomenology", and is strategically vague on how this phenomenology is to be shared. The idea that there is an aspect to reality, the concrete, over and above anything that can be captured represantationally, the abstract, the essence, and hence over and above anything empirical, or at least anything scientifically empirical, is quite common. So I do not expect to see dualists and materialists holding hands in agreement no matter what happens empirically.

Of course, many phenomenologists, like Husserl, would deny the dualism label, and claim instead that their position dissolves the material/ideal divide. Also, their non-empirical experience doesn't have to be mystical. Here is from Rinofner-Kreidl's Phenomenologist's Reply to Quine:"Phenomenology advocates are widening the concept of "experience" beyond that of sensual experience, thus permitting non-sensual experience referring to ideal objects indirectly situated in space and time "sekundär lokalisiert", i.e. by means of sensual objects to which they are connected. Therefore, phenomenological apriorism is committed to a special type of experience. It is not, on principle, independent of any experience whatever, as Kant considers a priori knowledge to be."


My questions:

1. How could dualists definitively prove the ontological uniqueness of mental states without these states becoming part of the domain of empirical sciences?

2. Can Dualism ever be distinguished from [non] reductive materialism?

I believe question #1 is flawed. If the dualists prove the uniqueness of mental states (or any other dualist claim) that then is able to become the domain of empirical science, they may have "lost" their dualist... is "status" the right word?

But in so doing, they would have "forced" the scientific community to accept their truth claims and expand their materialist view of the world to include an area of study that was previously denied to exist. Sort of a "lose the battle, win the war" story without even really losing the battle.

Then, I believe question #2 becomes irrelevant if you accept the above.

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