Incompatible Minds

Incompatible Minds

It is generally supposed that dualism is at least logically consistent, if riddled with other difficulties. There is no incompatibility between having both a mind and a body; a single thing (a person) could be both material and immaterial. One doesn’t rule out the other; you don’t contradict yourself if you say that a human being is both material and immaterial. We could call this psychophysical compatibilism. I (this thing) am (perhaps necessarily) a being with two natures, mental and physical. No one feels the need to develop a compatibilist account of the mind in order to make it compatible with the body. In this respect, the mind-body problem is unlike the free will problem: here there is a strong feeling that psychological freedom is logically incompatible with physical determinism. And more than a feeling, because the definition of freedom as the ability to do otherwise apparently contradicts the idea that everything we do is determined by our body and the past. The deterministic nature of the body rules out the freedom of the mind, given that the body determines the mind. But we don’t generally believe that the mind is incompatible with the body: we don’t think it’s contradictory to ascribe mind and body to the same entity, viz. a person or human being or rabbit. Having a physical brain is regarded as consistent with having a non-physical mind. Thus, dualism doesn’t suffer from incompatibility problems. I am going to argue, to the contrary, that it does.

Let’s start by considering the doctrine, worth examining in its own right, that all matter has a mental aspect (“material mentalism” to give it a name; it has others). The idea is that matter, ordinary lumps of matter, has two sorts of property: structural and mental. It has a dual nature, being both non-mental (“structural”) and mental (“non-structural”). For simplicity, let’s cash out “structural” as “spatial”; then we can say that material mentalism is the doctrine that all matter is both spatial and non-spatial—it has both aspects. It has an outside (what we perceive with our senses) and an inside (what we know from within by introspection). The doctrine may be viewed as extravagant or unexplanatory, but is it consistent? I think not. For it implies that the essence of matter is both spatial and non-spatial; and nothing (no single thing) can be both. Matter is thought to have a double essence (eyebrow-raising) and these essences are logically incompatible (impossible). Nothing can be both extended in space and not extended in space. Descartes never thought there could, which is why he assigned them to distinct substances (different things can instantiate contradictory attributes). In order to avoid this problem, you would have to reduce structure to mentality or mentality to structure, but the idea was to combine different essences into one thing: matter is said to psychophysical—that very stuff. The body is supposed to be both spatial and non-spatial. Notice that the claim is not that the structural features of matter (size, shape, etc.) have a mental essence; it is that these features coexist with mental properties quite distinct from them. Matter isn’t purely material; it is partially (but only partially) mental. So, matter (that stuff) has a double essence not a single essence. Descartes thought the essence of matter is extension; the material mentalist thinks that it is both extension and non-extension (what it’s likeness, thought, intentionality—whatever you think constitutes consciousness). But these are incompatible attributes. You could try going dualist about matter to avoid this problem—a piece of matter is really two substances or stuffs, each with its own characteristic essence. But then the structural stuff turns out to have no concrete nature—it is purely abstract. The mind is supposed to be what gives it a concrete intrinsic nature. Notice too that if we think away each attribute, we end up with nothing intelligible. Consider a possible world in which we have structure without mentality and one in which we have mentality without structure: the former is an abstract will-o-the-wisp, while the latter is disembodied and undeserving of the label “matter”. The whole picture is fraught with metaphysical difficulty. The point I am making now is that the psychophysical account of matter is not logically consistent, since (avowedly) the mental and the physical (“structural”) have incompatible essences. You can’t have a mentalistic theory of matter and a materialistic theory—what it’s like and structural (not what it’s like). You can’t have it both ways. Materialism about matter is consistent, and so is idealism about matter, but not part materialism and part idealism.  That is like supposing that the same thing is both determined and free: one negates the other.

Suppose you were to say that numbers have a material nature in addition to their abstract nature, or that moral values have a descriptive nature in addition to their evaluative nature. That would invite an accusation of inconsistency: numbers are not in space and yet material things are, and moral values are normative and yet descriptive properties are not. Something can’t be both; and no one ever said they could be. Abstract materialism is inconsistent and ethical descriptivism is too. The material mentalist is in the same boat and drowning by the same logic. Suppose we define the mental in terms of intentionality and the material in terms of the lack of intentionality (as has been done); then we can’t say that matter is both intentional and non-intentional. One excludes the other. Matter certainly doesn’t need intentionality to be matter; on the contrary. The same goes for a definition in terms of rationality or privacy or type of knowledge: the same thing can’t be rational and non-rational or private and not private or certain and not certain. Suppose we claimed that mind has a hidden material nature—it has a “structural” real essence. That would imply that the mind has all the properties of matter, including location and extension, in addition to its own defining properties; but these are contradictory. Of course, this is no problem for a classic reductive identity theorist, but that is not a form of double aspect theory—the type of theory I am criticizing. I am arguing that dualism is inconsistent when combined with an identity theory (in addition to its other problems)—dualism about matter in general and dualism about animal minds. Dualism implies what it says—dualism. You can’t combine dualism with monism. According to dualism, properly understood, an animal is two things not one—a mind and a body. Attempts to unite them under the heading of “person” or “self” are doomed to failure: the idea that there is a single entity, the person, that has both won’t work, since no single thing can have contradictory attributes. We are forced into materialism or idealism not a mixture of the two. The dualist has to say that matter and mind are disjoint existences—distinct substances, in the old terminology. They are not aspects of a third substance (the personor subject).  Monism is the indicated doctrine, of one kind or another, or outright substance dualism.

What should we say about the brain? Does it have two aspects? There is a temptation to say that it is both physical and mental—as the material mentalist says of matter in general. But this position is unstable: it implies that the brain is both extended and not extended, located and not located, solid and not solid, and so on. In so far as the brain is mental it is not extended, located, or solid (according to the dualist), but in so far as it is physical it is all these things. Then we have to say that the brain has contradictory properties, which is impossible. The best we can say is that some parts are mental and some physical; no part is both physical and mental. The brain is thus not one thing but a conjunction of two things; the essence of one is extension (etc.) and the essence of the other is what it’s likeness (etc.). You never have a fundamental duality of co-instantiated aspects. Duality of properties (essences) implies duality of substances. Not only are electrons never both mental and physical (contrary to material mentalism), brains aren’t either. An electron might be accompanied by a non-physical particle that is purely mental, and a brain might be accompanied by an immaterial soul, but there can’t be an entity that is both. The individuation of substances won’t allow it. Descartes never contemplated the idea of a single substance that is both material and immaterial, and he was right not to do so. This implies that property dualism is a misbegotten doctrine.[1]

[1] You might think this puts us in a tight corner, forcing us to choose between materialism and idealism, but there is a third way: postulate a third substance that can generate both mind and body (or brain) from unitary attributes—a kind of neutral monism. Dual aspect theories look like they give us the best of both worlds, but on closer examination they harbor incoherencies. To put it crudely, how on earth could ordinary matter contain elements of mind, given what we know of it? We would have to be very mistaken about it for this to be true. And physics would have to be extremely wide of the mark in its discoveries about matter. Don’t we know perfectly well that the hydrogen atom is not conscious? We have discovered a lot about the atom and never has mind sidled into view. What could account for the ignorance postulated by the material mentalist except that nothing of that kind is true? Do we really have no idea what an atom basically is? And could we have discovered its mental nature and never discovered its physical nature?  No, it has only one nature and we know pretty well what that nature is. (I realize that such pronouncements will not budge the hardened material mentalist, aka panpsychist.)