Chris Carter has recently posted an article challenging the idea that consciousness depends (for its very existence) on the brain. I’ve read it carefully and am underwhelmed. I have two general comments.

First, though Carter summarizes the evidence for mind-brain dependence well in the beginning, he has merely asserted–and comes nowhere near demonstrating–that William James’ “transmissive hypothesis” (a variant of what Paul Edwards’ called “the instrument theory,” the notion that the brain is merely an instrument of the soul) is “Just as consistent with the observed facts…” Saying so is one thing. Showing it is another. Nothing in this paper does the latter.

Second, it is simply false to characterize the explanatory value of materialism and dualism, with regard to the overwhelming evidence for mind-brain dependence, as on a par. Materialism clearly explains such evidence better in demonstrable ways.

Indeed, over 80 years ago, philosopher C. D. Broad’s intellectual honesty compelled him to concede as much. In a chapter titled “Empirical Arguments for Human Survival” in his 1925 classic on the philosophy of mind, The Mind and Its Place in Nature, before defending his own idiosyncratic form of dualism he dubbed “compound theory,” Broad writes:

“The view that the mind is existentially dependent on the organism and on nothing else is compatible with all the normal facts, and is positively suggested by them, though they do not necessitate it. And it is the simplest possible view to take. The theory that the mind merely uses the body as an instrument is difficult to reconcile with the normal facts; and it is doubtful whether there are any well-established [paranormal] phenomena that require it.”

Carter fails to address any arguments to the effect that materialism (broadly conceived to include property dualism) explains the evidence for mind-brain dependence much better than any form of substance dualism–arguments even present in his main target: Corliss Lamont’s The Illusion of Immortality. For instance, Carter writes:

“James then explores the various possibilities for the exact type of functional dependence between the brain and consciousness. It is normally thought of as productive, in the sense that steam is produced as a function of the kettle. But this is not the only form of function that we find in nature: we also have at least two other forms of functional dependence: the permissive function, as found in the trigger of a crossbow; and the transmissive function, as of a lens or a prism. The lens or prism do not produce the light but merely transmit it in a different form. As James writes

Similarly, the keys of an organ have only a transmissive function. They open successively the various pipes and let the wind in the air-chest escape in various ways. The voices of the various pipes are constituted by the columns of air trembling as they emerge. But the air is not engendered in the organ. The organ proper, as distinguished from its air-chest, is only an apparatus for letting portions of it loose upon the world in these peculiarly limited shapes.”

In The Illusion of Immortality, Corliss Lamont directly rebutted the prism analogy, which could easily be modified to cover the organ analogy as well:

“If the human body corresponds to a colored glass … then the living personality corresponds to the colored light that is the result of the glass…. Now while light in general will continue to exist without the colored glass … the specific red or blue or yellow rays that the glass produces … will certainly not persist if the glass [is] destroyed” (p. 104).

Yet Carter does not say a word in reply. And what about the simple point Paul Churchland raises in the introduction to his 1984 Matter and Consciousness:

“If there really is a distinct entity [an immaterial soul] 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 [the transmissive hypothesis], 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. Alcohol, narcotics, or senile degeneration of nerve tissue will impair, cripple, or even destroy one’s capacity for rational thought…. And the vulnerability of consciousness to anesthetics, to caffeine, and to something as simple as a sharp blow to the head, shows its very close dependence on neural activity in the brain. All of this makes perfect sense if reason, emotion, and consciousness are activities of the brain itself. But it makes very little sense if they are activities of something else entirely” (p. 20).

Carter goes on to say that all that the mind-brain dependence evidence shows is concomitant variation, not that mental activity is produced by the brain. But, as Hume has argued, if the issue is one of probability, this is precisely what concomitant variation implies: “The weakness of the body and that of the mind in infancy are exactly proportioned; their vigour in manhood, their sympathetic disorder in sickness, their common gradual decay in old age. The step further seems unavoidable; their common dissolution in death.” Indeed, John Stuart Mill even recommended the “method of concomitant variation” as one of the most reliable ways to reason from effect to cause, that is, to infer the most probable common cause of a number of effects.

Let’s look at Hume’s example. As brain complexity increases, mental abilities also increase (in Hume’s example, when you chart brain growth from infancy to adulthood; but also when differences in the intelligence of species with brains of varying complexity are compared). At the same time, as brain complexity decreases–in the progressive stages of Alzheimer’s disease (Hume’s “gradual decay”), say, or by progressively destroying more and more of the brain–mental acuity also decreases.

Mill’s method of concomitant variation recommends that we look for a prior condition that correspondingly varies with all events of certain type in order to identify that condition as a potential cause of events of that type. In this case, the question becomes: What always varies with the varying mental capacities of (say) different organisms? The answer: The complexity of their brains. As brain complexity goes up, mental abilities increase. As brain complexity goes down, mental abilities decrease. Brain complexity, then, causes mental ability. In short, the brain causes (or “produces”) the mind. If the William James’ transmissive hypothesis were correct, and the brain essentially only acted as a “transceiver” for consciousness, there is no reason to think that ever increasing mental complexity would require, in step, ever increasing brain complexity. A chimpanzee or a human being can type on a typewriter, but the greater complexity of what the human being types doesn’t require any increase in the complexity of their “instrument”–the typewriter. But increasing mental acuity does appear, without exception, to require increasing brain complexity. That observation is precisely the opposite of what one would predict if substance dualism were true, and exactly what we would expect if consciousness was a property of the brain.

Despite the clarity of this point, Carter concludes: “[T]he dependence of consciousness on the brain for the manner of its manifestation in the material world does not imply that consciousness depends upon the brain for its existence” [emphasis mine].

It seems to me that there is an intentional ambiguity here: what does Carter mean by ‘the manifestation of consciousness’? The most natural interpretation of ‘consciousness manifesting itself in the physical world’ is the behavior of conscious beings. But, as Corliss Lamont argued: “A severe injury to the head … may change an ordinarily cheerful man into a sullen and morose one subject to sudden fits of homicidal mania. If the brain and body are simply the instruments of the soul, we have to say in such a case that this personality is really still brimming over with joy and benevolence, but that unfortunately these sentiments can only express [“manifest”] themselves in dark glances, in peevish complaints and in violent attacks” (p. 100).

Evidently, then, ‘the manifestation of consciousness’ cannot refer to behavior, because it is demonstrable that manipulating the brain does not merely modify behavior, leaving the mind itself intact, but modifies mental functioning itself. LSD affects how you think, not merely how you behave. So what can Carter possibly mean by ‘the manifestation of consciousness’?