Is the Mind Identical to the Brain?

Is the Mind Identical to the Brain?

The mind-body problem is usually formulated as a problem about the relationship between mental and physical events, or about mental and physical attributes, or about “mental phenomena” and the brain. Seldom, if ever, is it formulated as a problem about what we call “the mind”, viewed as an entity bearing mental attributes. That is, we do not debate whether the substance denoted by “the mind” is identical to the substance denoted by “the brain”, to use traditional terminology. In other words, is the thing or object we call “the mind” identical to the thing or objectwe call “the brain”? If we view the mind as an organ, analogous to the heart or stomach, then the question would be whether the mental organ is identical to the brain organ. We would then be able to consider the doctrine of “organ identity”, just as we talk about type and token identity, or property identity. The organ identity thesis is thus the thesis that the organ that is the mind is identical to the organ that is the brain.

            It is important to see that the organ identity thesis does not entail either the type identity or token identity thesis. The mind could be identical to the brain and yet mental events are not identical to brain events: there are two kinds of events, ontologically separate, but they occur in a single substance, called both “the mind” and “the brain”. A single thing can host a variety of events—as the body contains both digestive and respiratory events—without those events being themselves identical. So the falsity of type and token identity theories would not entail the falsity of the organ identity thesis. If we think that standard identity theories are false, this holds out the hope that at least one form of materialism might be true—that the mind is just the brain. We then don’t have to accept a Cartesian dualism of substances or things, but can affirm that there is a single substance that has both mental and physical attributes. That substance can be described either as “the mind” or “the brain”.

            Why don’t philosophers debate this question more? I suspect it is because they think the mind is not a thing: they think that the definite description “the mind” does not denote an object of any kind, still less a physical object like the brain. Rather, when we talk of “the mind” we are really just talking about mental phenomena, so that the phrase “the mind” just means “all mental phenomena”. Then there is nothing left over to consider once we have considered mental events and mental properties—there is no “mental substance” whose relation to the brain we have not investigated. The brain is an individual substance, and maybe also the person, but there is no further individual substance called “the mind”. A person does not have a mind in the way he or she has a brain: the mind is precisely not like an organ of the body. Thus a philosopher might declare, “The mind is not an object!” It is some kind of category mistake to think that the mind is an object; and so there is no room for an identity theory of the object that is the mind.

            But surely this “no-object” view is mistaken. Maybe the mind is not a perceptible object or a spatial object or an object with mass, but that doesn’t imply that it is no kind of object. We certainly talk about the mind as if it is an object: the word “mind” is a count noun, allowing both the plural form and numerical quantifiers, and we have many singular terms purporting to refer to minds. Thus: “A mind is a terrible thing to waste”, “Great minds think alike”, “I have three first-class minds in my metaphysics class”, “Edith’s mind is like no other”, “He is out of his mind”, “My mind is totally exhausted”, “My mind is not identical to yours”, “I am in two minds about it”, and so on. These object-invoking locutions do not refer to bodies or to persons: they objectify the mind itself. As far as ordinary language is concerned, the mind is a thing—a substance, to use old-fashioned term. We need to be given a reason why our ordinary locutions are misleading–and I know of none. The question can then intelligibly arise as to whether this thing is or is not identical to the brain. We need not mean the whole brain: some parts of the brain have no mental correlate (that we know of), so we can exclude these parts from the thesis of identity. The claim will then be that the mind is identical to a part of the brain, say the cerebral cortex. Are there reasons to accept this claim, and are there reasons to doubt it?

            The reasons to accept it are familiar: we avoid Cartesian substance dualism, we respect Ockham’s razor, and we find a natural substance that can be the host and ground of mental events. We have empirically discovered that the brain is the thing referred by “the mind”—it is not the heart or some otherworldly non-spatial entity. If the mind is indeed a thing, then the brain is the thing that it most likely is. But are there any good objections to such a thesis? Objections to type and token identity theories will not entail objections to the organ identity thesis, but perhaps analogous objections will arise for that thesis. So it might be said that the brain could exist without the mind and that the mind could exist without the brain: we can imagine the two things apart in some possible world. That is, there can be zombie brains and disembodied minds: my brain might exist just as it is now but my mind does not exist, and my mind could exist without my brain existing. Note that the zombie claim is not that my brain could exist and host no mental events; it is that my brain could exist and my mind not exist (that specific thing), whether or not my mind itself instantiates any mental properties.

I think neither of these dualistic claims is credible: the existence of my brain just as it is now is sufficient for the existence of my mind (supervenience holds), and it is really not possible for the thing I call my mind to exist in the complete absence of my brain. Any intuitions we may have to the contrary can be easily explained away, so that we are free to accept the identity thesis of mind and brain (while possibly rejecting identity theses for mental events and properties). It is no more possible for the organ that is my mind to exist without my brain than it is possible for the organ that pumps my blood to exist without my heart existing.

A plausible assumption is that “mind” is synonymous with “organ that is responsible for thinking (etc)”, as “heart” is synonymous with “organ that pumps the blood”—at any rate, we can certainly imagine that the terms were introduced in that way. Then it has been empirically discovered that the mental organ is the brain, as it has been discovered that the blood-circulating organ is the heart. We might confuse epistemic possibilities with metaphysical possibilities in both cases—it might have turned out that minds and blood-circulators are different organs of the body (perhaps hearts and brains, respectively)—but once we know what the organs actually are we can claim necessary identity. My mind just is my brain and could not be anything else, as my blood-circulator just is my heart and could not be anything else. Some other mind need not be identical to a brain like mine (say, a Martian mind with a different type of “brain”), but my mind—this particular mind—is identical to that brain. It could not be otherwise.

            Are there difficulties stemming from Leibniz’s law? Well, there are certainly some interesting consequences: we can infer that the mind has a certain size, shape, and weight, since the brain does; and we can infer that the brain thinks and feels, since the mind does. Whatever is true of the brain is true of the mind and vice versa. But we can just accept these entailments as interesting consequences of an empirical discovery, rather like accepting that heat involves particles in motion or that the stomach contains acid—surprising, perhaps, but not refutations of the theory. It has turned out that the organ that thinks (the mind) has various physical characteristics, and that the organ in the head (the brain) has various mental characteristics: surprising, perhaps, but not reasons to reject the identification. A more challenging consequence is as follows: mental events occur in the mind; the mind is identical to the brain; therefore mental events occur in the brain. Similarly: neural events occur in the brain; the mind is identical to the brain; therefore neural events occur in the mind. Here we should remember that identity is symmetrical: if the mind is the brain, then the brain (or a part of it) is the mind—so whatever is true of the brain will be true of the mind. The mind therefore has biochemistry, runs on electricity, divides into two halves, is damp to the touch, and is nutritious when eaten. But again, these can be seen as interesting results, not reasons to reject the identity: surely both things (mind and brain) are likely to have hidden natures that science might disclose, which may not be anticipated by common sense. And then there is the point that it is a good thing if we find what substance mental events occur in, since we want them to occur in something natural and investigable: if they occur in the brain, then they do not occur in some supernatural entity, or in nothing. The identity of the organs doesn’t imply that mental events are neural events or have any of the properties of physical entities (like spatiality), since we are not assuming event identity; it tells us merely that the substance in which mental events occur is a physical substance with certain physiological properties. There is nothing even faintly reductionist about the organ identity theory with respect to mental phenomena.

            A thing (or substance) can easily instantiate different kinds of properties, so there is no logical difficulty about the brain being both a bearer of physical properties and a bearer of mental properties. It is much more difficult to make sense of a single event instantiating both mental and physical properties. According to the organ identity thesis, while the mind is the brain, mental events are not claimed to be physical events—indeed, token identity might be rejected as incoherent. Still less is there any commitment to type or property identity theory. In a sense, then, organ identity is a very weak form of materialism; but it is not trivial, because it excludes substance dualism and has some surprising consequences. It turns out that my mind is in my head, for instance, and that my mind has a specific weight. But that doesn’t mean that mental states are in the head or have weight. The book is on the shelf and has a certain weight, but that doesn’t mean that the story in it is on the shelf or weighs anything. Similarly, my brain turns out to be a thinking thing, given its identity to the mind, and it is conscious; but there is no need to assume that its other properties are likewise mental. If I have a conscious mind and an unconscious mind, then I have a conscious brain and an unconscious brain—I have two brains, as I have two minds (or a single mind with two parts). If someone has a brilliant mind, she has a brilliant brain; and likewise for mature minds, impoverished minds, petty minds, narrow minds, etc. But these propositions all look like natural consequences of an empirical discovery, not conceptual impossibilities. They simply result from the identity claim plus Leibniz’s law.  [1]

            The organ identity theory thus tells us that a single thing can be both mental and physical—so it is a kind of “double aspect” theory. It stands more chance of being true than the standard forms of identity theory, given the compelling objections that have been raised, and yet it is not trivial. It is not in any way a solution to the problem of consciousness, nor a theory of mental states more generally. It simply says that the mind is identical to the brain, i.e. that these two entities are one and the same. The mind, then, is identical to a part of the body. This may not be as much materialism as we would like, but at least it avoids one kind of dualism.

Colin McGinn

  [1] It is possible to weaken the theory in order to avoid the consequences of Leibniz’s law, by replacing identity with constitution. Then we don’t have to attribute every property of the mind to the brain and vice versa. But I like the boldness of the straight identity theory.