of brain and mind

Of Brain and MindConsciousness Explained. by Daniel C. DennettReview by: Richard A. WatsonThe Quarterly Review of Biology, Vol. 67, No. 3 (Sep., 1992), pp. 346-347Published by: The University of Chicago PressStable URL: http://www.jstor.org/stable/2830653 .

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346 THE QUARTERLY REVIEW OF BIOLOGY VOLUME 67

OF BRAIN AND MIND

RICHARD A. WATSON

Department of Philosophy, Washington University St. Louis, Missouri 63130 USA

A review of CONSCIOUSNESS EXPLAINED.

By Daniel C. Dennett; illustrated by Paul Weiner. Little, Brown and Company, Boston (Massachusetts). $27.95. xiii + 511 p.; ill.; index. ISBN: 0-316- 18065-3. 1991.

Consciousness Explained is an extended and well- written argument for the thesis that all mental phenomena-sensory experience, intentionality and consciousness -are physical manifestations of the material brain. Most scientists and many philoso- phers accept methodological physicalism and onto- logical materialism on the pragmatic ground that science would otherwise be impossible. That physical materialism provides reliable explanations and predictions for doing things in this world is, however, not in itself a conclusive argument against the metaphysical claim that besides material stuff there is also mental stuff in the world. Nor is it an argument against the claim that there is only mental stuff in the world, of which material things and physical events are mere aspects or construc- tions. The notorious difficulty of specifying criteria according to which one can determine whether the world consists only of material or mental stuff- or of both, as is required by Christians who separate the soul from the body -and the fact that it really makes no difference to the advancement of pragmatic science what the answer is, leads many phi- losophers to deny that metaphysical questions make any sense, or at the very least to assert that their answers make no difference to the way we perceive the world. Obviously, this response is not acceptable to Christians and others who would like to believe that we have immortal souls that survive the death and disintegration of our bodies. Dennett comprehends that, in explaining consciousness, the ultimate prize at issue is the human soul. He points out that the major obstacle to research on the scientific explanation of the mind is opposition by those who do not want to know, for fear that they will lose their souls. He is not sympathetic to their stance.

In the 17th Century, skeptical arguments against the possibility of knowledge were so perva- sive that Marin Mersenne wrote an enormous book, La Verite des Sciences (Toussainct du Bray, Paris, 1625), packed with things we know. His was a faith in the rise of modern science. Dennett's book is also packed with things we know about the mind and the brain. The cumulative impact of this

information is meant to convince readers that the correlation of physical phenomena in the brain with mental phenomena in the mind constitutes an argument that the mind in fact is the brain. The identity goes in that direction because the detailed, experimental scientific work of neurophysiology is taken to be primary to the detailed, experimental scientific work in cognitive psychology. This pri- macy is based on the dependence of neurophysiology on physics, and on the fact that behavioristic (physicalistic) psychology bulks much larger than pure cognitive psychology. Most of all, however, neurophysiological phenomena can be explained and predicted in the causal nexus of physical science. Mental phenomena understood as ontologi- cally independent of matter have no causal efficacy in the material world, and thus cannot be used to explain and predict material phenomena. Given that mental items and events can be correlated with neurophysiological items and events, however, one can argue that the mental is explained by the physical, and from this it seems plausible to con- clude that the mental is the material. What we are really referring to when we use mental terms, Dennett argues, are states, processes, and events in the brain.

What is lost, mentalists argue, is all consciousness of sensory experience that makes life worth living. If pain and pleasure are only nerve im- pulses, love and joy brain states, and the stream of consciousness merely parallel processing in a bag of a billion neurons, my self-consciousness, self- interests and self-respect are lost. No! the ghost of Descartes moans, I am a mental thing that thinks. Destroy my body, but you cannot destroy the conscious me. Dennett's response is not delicate. Sen- sory experience is an illusion, he says, and consciousness is present neither as an unbroken stream, nor is it manifested as a single self. Dennett reports the evidence that different configurations of the same brain can be manifested as separate selves, sometimes at the same time. Selves can be obliterated by disabling parts of the brain. Differ- ent selves could even succeed one another without any one of them noticing the shifts, because they share the same information and activity network in one brain. We are not oblivious to this multi- plicity of mind for we notice it in others and often (if only vaguely) in our selves. And so on.

To the argument that mental phenomena are just totally unlike the physical states and events in



SEPTEMBER 1992 NEW BIOLOGICAL BOOKS 347

the material brain, and thus cannot be identical with them, Dennett points out that scientific explanation often consists of explaining the presence of one thing, e.g., a table, by the presence of other things, e.g., a swarm of atoms. Do we make the classic blunder of saying that there are two different tables, or do we admit that there is just one table, made of atoms? But the table is colored and atoms are not. So? Many chemical compounds exhibit features not present in the elements that make them up. Surprising, perhaps, but that's the way the world is. Excite a bunch of neurons and you get sensory experience. A table is a batch of atoms, but you see a table. A visual image, e.g., is a dispositional state of the brain, but you see a visual image. That is what scientific explanation consists of: identifying tables, say, with atoms, to show how things work in the causal nexus. The puzzle of how mental phenomena can exist without having influence in the causal nexus can thus be solved: Mental phenomena do in fact have causal influence because they are identical with the neurophysiological phenomena in the brain.

Dennett does not in fact draw his conclusion this way, although he sets up all the material for doing so. What Dennett actually says is that visual im- ages, for example, are illusions, and that we just seem to see them but really do not. This is a remnant of his training by Gilbert Ryle, whose attempt to deny the reality of sensory experience has been abandoned by almost everyone except Dennett. When Dennett says, as he often does, that mental phenomena actually are real because they are physical phenomena in the material brain, he ought also to admit that their properties are sensory.

Sensory experience and consciousness are easy to account for physically (which does not at all mean that mentalists accept these accounts). The real crux is intentionality. How can something material have the property of being of or about, the property of pointing to or intending something? If an idea is a brain state, how can a brain state have content or meaning? Don't you need an intender if you have intentions? This problem comes up on page 365, and on page 457 Dennett stresses that his introduction of "presentments" as being "like speech acts with no Actor and no Speech . .. and then [his] replacing the presentments with 'events of content-fixation' [is] the crucial move in [his] whole theory." He goes on to say that his "fundamental strategy has always been the same: first, to develop an account of content that is independent of and more fundamental than consciousness -an account of content that treats equally of all unconscious content-fixation (in brains, in computers, in evolution's 'recognition' of properties of selected designs) -and second, to build an account of con-

sciousness on that foundation. First content, then consciousness." As background to the present book, Dennett refers the reader to two of his pre- vious books, The Intentional Stance (The MIT Press, Cambridge, 1987) and Brainstorms (Bradford Books, Cambridge, 1978); see also his earlier Con- tent and Consciousness (Routledge & Kegan Paul, London, 1969).

Can material entities be intentional? Dennett argues that they can be endowed with meaning in the natural course of physical evolution, not because they are given content by a separate conscious self, but because the conscious self evolves in parallel with and out of elementary, unconscious content-fixing neuronal activity in the brain. He concludes by saying that formerly we studied the mind using Descartes's metaphor of a little man inside the head reading off the information that comes into the brain. Dennett's metaphor is that of the brain as a computer, not a computer programmed and read by someone else, but a computer programmed by evolution to be partially self-programming and thus capable of self-con- sciously creating a narrative stream of thought. In the old dualistic system, mind-body interactions are magic because they cannot act causally on one another. But if we adopt mind-brain materialism and treat sensory experience, intentionality, and consciousness as physical phenomena, then we can bring the mind within the realm of science. This is the grand program to which Dennett's work is a contribution.

One cannot read Dennett's book without a program. In An Invitation to Cognitive Science (Basil Blackwell, Oxford, 1991), Justin Leiber provides the background for understanding the mind-body problem that Dennett and contemporary neurosci- entists are trying to solve. The notion that there is an immaterial self arose in part because, at least since Plato, it has been difficult to understand both how we can know and learn so much, and how we can be conscious of this knowledge. Descartes -

a total mechanist in his neuroscience -thought it impossible for a mere machine to be conscious, and so postulated an immaterial self. Leiber traces the advance of the man machine against the ghost in the machine from Descartes through La Met- trie, Mary Shelley, Babbage, Russell, and Turing. In his chapter, Meaning Must Have a Stop, he sets out the problems of meaning and content-fixing. In general, Leiber's book provides a necessary background on intentionality and consciousness as they arise and pose problems in philosophy and in contemporary cognitive science. Reading Leiber's book in conjunction with Dennett's will help one understand the problems of the computer metaphor, the players, and the moves in the game.



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