I have started studying philosophy of mind and I am currently reading an introduction to the field. The first topic that is presented in the book is dualism of the Cartesian brand, and the case for it is made, roughly, thus:

  1. Material objects are characterized by such things as extension, shape, definite location in space and being made of elementary particles which could be described by a physical theory
  2. Mental objects, such as sensations, perceptions and thoughts, exist
  3. Sensations, perceptions and thoughts are not extended, have no shape nor definite locations in space, and are not made up of particles
  4. Therefore, sensations, perceptions and thoughts are not material.

Honestly, it seems a good argument to me. If I think about a desire I am feeling, for istance, I could argue that it is my body, and so it would have a location in space, but it would not make sense to me to say that this desire has a shape, or that its position could be exactly pinpointed, or that it could be observed or detected through technological devices (even potentially!).

This notwithstanding, objections to the argument are not considered in the rest of the book. The only thing it has to say about dualism is that it demands an explanation of how the immaterial and the material interact causally. A lot more space is devoted to potential refutations of the knowledge argument, the zombie argument and the likes.

Even perusing some literature on the topic, the closest thing I have found to a discussion of this argument is in Smart's paper Sensations and Brain Processes. The author seems to argue, at least as far as I can grasp, that premise 2 is false: there is no such thing as a perception or a sensation or a thought, but only experiences of having a perception, or a sensation or a thought.

Besides this, I could not find references to the argument even in anti-materialist treatments (except for the book I'm studying, of course).

Why is this argument overlooked? Is it that bad?

  • In addition to Smart's objection to premise 2, premise 3 may be considered problematic. If one believes that mental "objects" are identical to the physical firing of neurons, then mental objects do have extension, shape, and definite locations in space, and they are made up of material particles. According to this view, the desire to drink a cup of coffee is a physical brain state with all of the physical properties mentioned above. Also note that the choice of the word "object" is contrary to the ideas you are expressing. Perhaps phenomena would be a better choice.
    – nwr
    Jan 6, 2016 at 4:18
  • So, are you arguing that premise three is begging the question?
    – Adrian
    Jan 6, 2016 at 4:21
  • Premise 3 is certainly problematic for a physicalist/materialist. On the plus side, there are aspects of consciousness, such as qualia, which have so far resisted neuroscientific techniques aimed at establishing "neural correlates" and there are persuasive arguments that such correlates will never be identified.
    – nwr
    Jan 6, 2016 at 4:26
  • 3
    I would definitely summarize the whole argument as "Premise 3 is begging the question". But so it Premise 1. We have decided, after a long search in physics that what we see as material objects are mostly empty space, that they do not really have clear boundaries, that the material that makes them up is not really localized, and that elementary particles are not elementary, but are bundles of energy and can be broken down and recomposed So they lack extension, shape, locality and construction. Between those two, the argument is no so much wrong, as pointless.
    – user9166
    Jan 7, 2016 at 0:46
  • "Greenness Disappears"
    – user16869
    May 13, 2016 at 1:45

6 Answers 6


This argument is a variation on what Kitcher calls the "rational psychologist's fallacy" in Kant's Transcendental Psychology. It is a particular case of the argument from ignorance fallacy, and was addressed already by Kant in Critique of Pure Reason. In the OP version of the argument the fallacious reasoning is rolled into using premise 3. Sensations, perceptions and thoughts are effects implemented by something, and one can not move from description of effects to conclusions about the nature of something that implements them, unless one actually knows how they can be implemented. So "not extended, have no shape nor definite locations" are no more relevant than the same statements about say heat or beauty.

In the original version of the fallacy sensations, perceptions and thoughts were replaced by "the unity of thought", and Kant pointed out that this sort of reasoning cuts both ways. Here is Kitcher's summary of Kant's argument in the Second Paralogism:

"If Rational Psychologists are permitted to argue for the simplicity and immateriality of the soul by claiming that they do not see how a material substance could realize the unity of thought, then materialists would be free to employ the same strategy to "establish" the opposite conclusion. Since the latter do not understand how an immaterial substance could realize the unity of thought, they may claim that the soul is material".

Here is another version of the same fallacy with immateriality replaced by intentionality, which is due to Searle:

"It is not because I am the instantiation of a computer program that I am able to understand English and have other forms of intentionality... but as far as we know it is because I am a certain sort of organism with a certain biological (i.e., chemical and physical) structure, and this structure under certain conditions is causally capable of producing perception, action, understanding, learning, and other intentional phenomena".

As Kitcher points out:

"In this passage Searle indulges in exactly the sort of argument from ignorance that Kant warns Rational Psychologists against... The problem with both arguments is that, although we have certain abstract descriptions of thoughts (they must be unified, they must be intentional), we do not have the slightest idea what kinds of things might be able to instantiate those properties. Proponents of such arguments disguise this fact, by announcing that souls possess the requisite unity or that brains possess the requisite intentionality. But these bold claims do not rest on an understanding of how anything could possess such properties; they are supported entirely by the antecedent conviction that it is brains or immaterial souls that do the thinking."

  • 4
    @Alexander S King I often get the impression that many modern debates in philosophy of mind and language would be dissolved, or at least would take a more constructive form, if their participants seriously engaged Kant's critical objections to their presuppositions. Not kidding! I see Quine as asking for just that in contemporary terms on analytic/synthetic distinction, metaphysical possibility, and indeterminacy of translation, but it is a cry in the desert.
    – Conifold
    Jan 7, 2016 at 0:52
  • 1
    but the same kind of fallacy prevents materialist from claiming the mind is material, doesn't it? are materialists entitled to say anything better than "we do not know how the mind can be understood in terms of materialism"?
    – nir
    Jan 7, 2016 at 7:24
  • 3
    @nir I rarely see materialists argue inductively like "we see thoughts attached to bodies, therefore they are material", they usually go hypothetico-deductively "assuming they are material we can build models of thinking" and point to neuroscience for partial progress. They then have not metaphysical but methodological advantage over the alternative in that their hypothesis enables a research programme that has hope of gaining insight into mental workings.
    – Conifold
    Jan 10, 2016 at 21:04
  • 1
    @Conifold, "the latter do not understand how an immaterial substance could realize the unity of thought, they may claim that the soul is material"... This objection does not make sense to me. If someone makes the claim that "integers each have particular smells"... the claim is nonsensical. Integers are fully defined... there's no doubt that integers don't have smells. The argument, "Just because you cannot conceive of how integers can't smell does not mean they can't." Similarly, programs are fully defined. Material objects are fully defined. They can't magically take other properties. Apr 2, 2016 at 23:28
  • 1
    @Ameet Integers are not fully defined, there are inequivalent versions of arithmetic and undecidable sentences in all of them, but they are at least of our own making. Material objects are not, the empirical "definition" is provisional and open to revision, and we also know little how sufficiently complex systems of even well understood material elements would behave. So far we haven't even deduced chemical properties from quantum mechanics, but few argue that acids are immaterial.
    – Conifold
    Apr 4, 2016 at 21:11

I think that argument would have been very effective a few hundred years ago. However, science has been clawing away at Premise 3. It is no longer immediately obvious that sensations have no shape or location, due to modern neurology. In fact, one might even dare to argue that premise 3 is obviously false. Consider that they check newborn's hearing within the first 24 hours by putting electrodes on their skull and playing soft clicks in their ear while recording the electrical activity. That strongly suggests there is a location to the sensation of hearing.

The focus on things like knowledge and p-zombies is more common because they are considered hard definitions to pin down. You think you know what knowledge is, until you really start to try to define it, and then you quickly realize that you know very little about how you know things. Likewise, p-zombies push at the definition of "consciousness" itself. They force us to ask question like "is consciousness even an observable property?"

The complicated part is when you start talking about mental processes supervening onto physical processes. It can get harder to tell whether something is a pure mental process, or if it is a physical process whose behavior is well described as though it were a metaphysical mental process.

  • Sam Harris said: "Consciousness is the one thing in this universe that cannot be an illusion."
    – user16869
    May 13, 2016 at 1:54
  • @nocomprende Then that certainly perscribes some limits on the meaning of either "consciousness" or "illusion," doesn't it?
    – Cort Ammon
    May 13, 2016 at 2:49
  • I am not sure I follow. If illusions are limited, that is good right? Ideally, there would be no illusions, so limit them away! Consciousness is limited also. I don't know any omniscient people. What is the problem there? Limited things are therefore worthless? Well, throw the universe away then.
    – user16869
    May 16, 2016 at 2:00
  • @nocomprende I did not say that illusions nor conciousness were limited. I said the meaning of those words are limited by making such a powerful assertion. It means one must choose a meaning for those words carefully such that the assertion does not prove false. One might even miss the entire point of others who use those words differently, just to uphold such an assertion. The consequence may be quite extreme. Its entirely possible the only entities meeting Sam Harris's assertion are unobservable, and as such can never be an illusion.
    – Cort Ammon
    May 16, 2016 at 5:04
  • Mmkay, I was thinking that we have zillions of examples of conscious beings: humans, pets, many other animals. I see consciousness as a continuum, verging downward into awareness, extending to the interactions of elementary particles. For me, 'consciousness' basically is synonymous with 'reality'. Not sure if Harris felt that way, he was simply arguing for our own experience. To me, the meaning of 'illusion' is anything that we think exists, apart from our experience. It is a big world.
    – user16869
    May 16, 2016 at 12:18

Of course, sensations and other mental processes are not material. Electrochemical processes were unknown to Descartes. His characterization of res extensa derives from the restricted mechanical view of his time.

But when repeated today, the argument is a bit outdated: Today we say that mental processes are a kind of information processing, i.e. the basic term is information. Information processing always needs a material or better a physical substratum, e.g. nerve cells and the electrochemical processes of information processing. Information cannot be equated with these physical processes, but information presupposes the existence of these processes. A first bridge between physics and information theory is the concept of the entropy of a message. In the context of neuroscience this bridge has to be broadened to join physics and informatics and create a monistic and scientific view which incorporates mental processes.

Summing up: Descartes is right that mental processes are not material. But the scope of his approach is too narrow to be relevant for today's investigations.

  • but computation is a mechanical process. you can create a computer brain from cog wheels, you don't need electronics or quantum phenomena
    – nir
    Jan 6, 2016 at 15:06
  • @nir I consider the algorithms the important aspect of computation, not which hardware is used.
    – Jo Wehler
    Jan 6, 2016 at 18:14
  • But at the end what you have in a computation that is being carried out, are just cog wheels turning and pushing on each other. Where in that mechanical mill, can you find anything immaterial?
    – nir
    Jan 6, 2016 at 18:27
  • 1
    @nocomprende, in the case of a machine built by humans, what you call a purpose is external to the system of cogwheels. It is a thing in the mind of a human. we can argue separately if that thing in your mind is material or not but it is irrelevant to the turning of the wheels in the machine. if you consider the machine alone then where is the purpose? where is anything immaterial in its operation? another person can examine it and describe its operation and declare its operation can be described by a particular algorithm or principle, say evolution, but that is just an external description.
    – nir
    May 13, 2016 at 5:43
  • 1
    The turnings of the wheels carry out the purpose, just like when you work for a company, you carry out your purpose. Why is this so hard for people to understand? What is this mythical layer that they keep creating? Your job is an "external description". What are you when you are doing your job, besides just some protoplasm occupying space and producing heat? Well, other blobs of protoplasm happen to want you to do whatever you are doing. Are wants thoughts? Are they immaterial? I think people are just trying to hard. They are thinking too hard. Just observe what is.
    – user16869
    May 16, 2016 at 1:58

What the problems in the argument are, and why it is overlooked, are two different questions.

1) Every argument has problems, so pointing out its problems does not explain why it is overlooked.

2) Is it really overlooked? I don't know. If people in this community do not come up with references I would appreciate if you could contact the author of said book with this question and let us know the answer here. (what is the name of the book?)

3) If it is indeed overlooked, then one possible explanation may be found in Peter Unger's recent bashing of philosophy:

What philosophers are in search of — and they don’t realize this — is generalizations that aren’t open to any conceivable possible counterexample, however far-fetched. These counter-instances don’t have to be at all realistic. So they put forth these offerings. Almost always, these offerings fail, and colleagues come up with counter-instances. When they don’t fail, they turn out to be trivial. Virtually all of them are analytically correct, though philosophers don’t realize it.

Generally, though, they’re mostly incorrect offerings, with counterexamples, and it keeps changing and keeps changing, until everyone becomes bored with the topic, and then they go on to something else. It’s not as though anything ever gets established, except for very trivial things, nor is it that anything ever gets refuted. Rather, things become old hat and fashions change. But this general way of doing things hasn’t changed. In about seventy or eighty years, as far as I can tell, in terms of mainstream English-speaking philosophy.

  • Seems more like about 2500 - 3000 years. I have this feeling about Philosophy too. Nonduality cuts through a lot of the illusory thinking and pointless conceptualizing.
    – user16869
    May 13, 2016 at 1:56

What is wrong with the proposition is that it has two mutually contradictory statements. If statement 2 is true, then statement 3 is false; if statement 3 is true, then statement 2 is false. This ensures that at least one statement,out of three, is false. Therefore, the conclusion is false.
This all comes about from the "normal" understanding of exist - an object exists, if it can be perceived by at least one of the 5 human senses.

  • What if the "object" in question is a Perception? Or an Experience? Does 1 exist? Does Fairness exist? How about the rules of a game?
    – user16869
    May 13, 2016 at 1:57

Thoughts are not immaterial. Thoughts are neural activity, period. They do not float around in your head and are not dissipated or stored intact. They are neural "experiences" that can be replayed as "memories." They seem to be immaterial due to the brain's perception mechanism that we identify with as "self." "I" have this thought of "going to get ice cream." The "I" is also neural activity; self does not exist as an entity.

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