Mind and Body
"The Emergence of Spirit and Matter", attributed to Shivdas, painted ca. 1828 during the reign of Maharajah Man Singh, Marwar (now Jodhpur), Rajasthan, northwest India. From Folio 2 from the Shiva Purana, now in the Mehrangarh Museum. The painting is influenced by the ascetic Nath sect of yogis. The left panel represents the "formless Absolute" that preceded Creation. In the center panel, Spirit or Consciousness (the male figure) and Matter (the female figure) are linked through their gaze and posture. In the right panel, Spirit and Matter are separated, with their arms crossed, no longer looking at each other. From Garden and Cosmos: The Royal Paintings of Jodhpur, exhibit at the Arthur M. Sackler Gallery, Smithsonian Institution, 2008-2009.
Consciousness has many aspects, but the fundamental feature of consciousness is sentience or subjective awareness. As the philosopher Thomas Nagel put it in his famous essay, "What Is It Like To Be a Bat?" (1979),
The fact that an organism has conscious experiences at all means, basically, that there is something it is like to be that organism. There may be further implications about the form of the experience; there may even (though I doubt it) be implications about the behavior of the organism. But fundamentally an organism has conscious mental states if and only if there is something that it is like to be that organism -- something it is like for the organism. We may call this the subjective character of experience. It is not captured by any of the familiar, recently devised reductive analyses of the mental, for all of them are logically compatible with its absence. It is not analyzable in terms of any explanatory system of functional states, or intentional states, since these could be ascribed to robots or automata that behaved like people though they experienced nothing.The relation between mind and body is one of philosophy's great problems, but consciousness plays a special role in making it problematic. It's no trick to make a machine that processes information (well, I can say that now!). All you have to do is take stimulus inputs and process them in some way so that the machine makes appropriate responses. Your home computer does this. So does a 19th-century Jacquard loom. From this perspective, as the computer scientist and artificial intelligence pioneer Seymour Papert once put it, "The brain is just a machine made of meat". The trick lies in making a machine that is conscious.
As Nagel put it in his "Bat" essay,
"Consciousness is what makes the mind-body problem really intractable. Without consciousness, the mind-body problem would be much less interesting. With consciousness, it seems hopeless."How did we get to this point?
A Philosophical Disclaimer
I'm not a philosopher, and I don't
have any advanced training in the history and
methods of philosophy -- or any elementary training,
either, for that matter. In trying to make
sense of philosophical analyses of the mind-body
problem, which I think is necessary in order to have
some perspective on the scientific work, I have
relied on my own common sense, the tutelage of John
Searle (who should not be held responsible for any
of my own misunderstandings), and several excellent
These authors don't discuss the evolution of mind and consciousness, but I'll have something to say about this topic later, in the lectures on "The Origins of Consciousness".
In addition to these popular general
introductions to philosophyI have particularly
relied on the following:
The modern debate about mind and body has its origins at the beginnings of modern philosophy, with Rene Descartes (1596-1650), a 17th-century French philosopher who lived and worked in Holland for most of his life, and the other thinkers of the Enlightenment.
Descartes argued for a strict separation between human beings and animals.
Body and Soul, Body and Mind, Body and Brain
most Western philosophers who came before him,
Descartes was a layman, but he was also a dutiful son of
the Catholic Church. Like Galileo, he advocated a
heliocentric view of the universe. But when he
heard of Galileo's persecution, he suppressed his own
view. As it happens, Church doctrine also
influenced Descartes' thinking about body and
mind. Descartes made his argument for
dualism in part on the basis of his religious beliefs:
Church doctrine held that Man was separated from animals
by a soul, and for Descartes, soul was equivalent to
mind, and mind was equivalent to consciousness.
Mind is the basis for free will, which provides what we
might call the cognitive basis for sin.
However, Descartes' dualism was also predicated on rational grounds. It just seemed to him that body and mind were just -- well, somehow different.
And so it seems to the rest of us,
too. Paul Bloom, in Descartes'
Baby (2004), notes that even young children
-- once they have a concept of the mind, a topic
we shall discuss later in the lectures on "The
Origins of Consciousness" -- appear to
believe that their minds are somehow
distinct from their bodies.
although they know about brains,
they appear to construe their brains as "cognitive
prostheses" that help them
think, instead of organs
that actually do all our thinking.
It has been suggested that
dualism is intuitively appealing because
the brain does not perceive itself, the
way it perceives sounds
and lights, the rumblings
of your stomach and dryness of your mouth, your heart
beating rapidly and your face flushing.
There's "no afference in the brain" --
just (just!) interneurons processing
environmental events, manipulating thoughts, and
organizing responses. We can't feel
Of all of Descartes' ideas, dualism is perhaps the most influential. Not for nothing, I suppose, when he died his skull was buried in a different place than the rest of his body (see Descartes' Bones: A Skeletal History of the Conflict Between Faith and Reason by Russell Shorto).
Descartes' dualism is also an interactive
dualism. Mind and body are composed of separate
substances, but they interact with each other.
But aside from locating it in the pineal gland, Descartes had no clear idea how this mind-body interaction took place. This is what the philosopher G.N.A. Vesey referred to as the Cartesian impasse (in The Embodied Mind, 1965).
It is now known that the pineal gland is sensitive to light, and when stimulated releases melatonin, a hormone that is important for regulating certain diurnal rhythms. The pineal gland may not be where mind and body meet, but it does seem to be an important component in the biological clock.
And, for that matter, he was wrong on the first point, too: close microscopic examination reveals that the pineal gland is divided into two hemisphere-like structures. But Descartes had no way of knowing this, so we shouldn't count it against him.
Mind and Body in Opera
Many later philosophers tried to find a way out of, or around, the Cartesian impasse. In so doing, they adopted a dualistic ontology, but not necessarily of Descartes' form, involving different interacting substances.
Nicholas Malebranche (1638-1715) proposed a view called occasionalism. In his view, neither mind nor body has causal efficacy. Rather, all causality resides with an omniscient, omnipotent God. The presence or movement of an object in a person's visual field is the occasion for God to cause the visual perception of the object in the observer's mind. And the desire to move one's limb is the occasion for God to cause the limb to move.
Baruch Spinoza (1632-1677) proposed dual-aspect theory (also known as property dualism). In his view, both mind and body were causally efficacious within their own spheres. Physical events cause other physical events to occur, and mental events cause other mental events to occur. But both kinds of events were aspects of the same substance, God. Because God cannot contradict himself, he thus ordains an isomorphism between body and mind.
Gottfried Wilhelm Leibnitz (1646-1716) proposed psychophysical parallelism. In his view, mind and body were different, yet perfectly correlated. Leibniz's parallelism abandons the notion of interaction. He saw no way out of Descartes' impasse, because he could not conceive of any way for two different substances, one material and one immaterial, to interact. He also rejected occasionalism as mere hand-waving. The only remaining alternative, in his view, was parallelism: when a mental event occurs, so does a corresponding physical event, and vice-versa. This situation was established by God when he created Man, and doesn't make use of the pineal gland or anything else.
These neo-Cartesian views may seem silly to us
know, but it is important to understand why people were so
concerned with working out the mind-body problem from a
First, there was the influence of Catholic religious doctrine, which held that humans possessed souls that distinguished them from mere animals. Today, the Roman Catholic Church has no problem with the theory of evolution, for the simple reason that, in their view, Darwn's theory applies to the evolution of bodies, whereas souls, including mind and consciousness, comes from God. The equation of soul with mind creates the mind body problem.
We know, intuitively, that mind somehow arises out of bodily processes, but we also know that mind somehow controls our bodily processes. This "somehow" is the great sticking-point of dualism. Apparently, the only way out is to abandon dualism for monism, the ontological position that there is only one kind of substance. But if there is only one substance, which one to choose?
Faced with the
choice, some monists actually opted for mind over body.
Chief among these was George Berkeley (1685-1753, pronounced
"Barklee", like the basketball player), the Anglican bishop
whose poem, "Westward the course of Empire wends its way",
inspired the naming of Berkeley, California (pronounced
"Berklee", like the music school in Boston). By
insisting that there is no reality aside from the mind that
perceives it, Berkeley articulated a position variously known
as immaterialism, idealism, psychic monism,
or mentalistic monism. For Berkeley, only two
types of things exist: perceptions of the world, and the mind
that does the perceiving.
A Zen koan asks: If a tree falls in the
forest, and nobody hears it, does it make a sound? For
Berkeley, the answer is a firm No. Berkeley's
philosophical doctrine, known as esse est percipi -- "to be is to be
perceived" holds that nothing exists independently of
the mind of the person who perceives it.
Obviously, there's no sound unless the
mechanical vibrations in the air generated by the
falling tree fall upon the eardrum of a listener.
But for Berkeley, the tree itself doesn't exist unless there's
present to perceive it. Strange as it may
seem, Berkeley was what we would now call a
philosophical "empiricist". He believed, like
Locke and other empiricists, that all our
knowledge of the world comes from our
sensory experience; but he concluded that if
all we know of the world is our sensory
impressions of it, then mind itself,
not matter, must be the fundamental
James Boswell (1740-1795) tells the story of what happened when he told Samuel Johnson (1709-1784), about his (Boswell's) inability to refute it (Boswell, Life of Johnson, Vol. 1, p. 471, entry for 08/06/1763):
Still, immaterialism has attracted some adherents in the years since.
After we came out of church we stood talking for some time together of Bishop Berkeley's ingenious sophistry to prove the non-existence of matter, and that every thing in the universe is merely ideal. I observed, that though we are satisfied his doctrine is not true, it is impossible to refute it. I shall never forget the alacrity with which Johnson answered, striking his foot with mighty force against a a large stone, till he rebounded from it, "I refute it thus.".
Chief among these, the American psychologist Morton Prince held that consciousness was a compound of mental elements which he called -- no kidding -- "mind-stuff" (in The Nature of Mind and Human Automatism, 1885). In his view, all material elements possessed at least a small amount of mind-stuff; when these elements are combined, their corresponding mind-stuff is also combined, so that consciousness emerges at a certain level of the organization of matter. At first glance, this looks like property dualism, but Prince was really an immaterial monist. In his words (and punctuation):
[I]nstead of there being one substance with two properties or 'aspects,' -- mind and motion [extension], -- there is one substance, mind; and the other apparent property, motion, is only the way in which this real substance, mind, is apprehended by a second organism: only the sensations of, or effect upon, the second organism, when acted upon (ideally) by the real substance, mind.
monists opted for body over mind, a position variously known
as materialist monism, or simply materialism.
Among the first materialist monists was Julien Offray de la Mettrie (1709-1751), who claimed that humans, like animals, were automata, with their behaviors governed by reflex. The only difference between humans and animals was that humans were conscious automata, aware of objects and events in the environment, and of their own behavior. For de la Mettrie, mental events exist, as Descartes had said, but they are caused by bodily events and lack causal efficacy themselves. De la Mettrie's book was promptly burned by the Church, and de la Mettrie himself sent into exile.
But his essential position was subsequently adopted by Pierre Jean Georges Cabanis (1757-1808). In a formulation that will be familiar to those who have read much more recent work on the mind-body problem, Cabanis claimed that
"Just as a stomach is designed to produce digestion, so a brain is an organ designed to produce thought".
The views of de la Mettrie and Cabanis set the stage for of epiphenomenalism, a term coined by Shadworth Holloway Hodgson (1832-1912). In Holloway's view, thoughts and feelings had no causal efficacy. They were produced by bodily processes, but they had nothing to do with what the body does.
Whereas de la Mettrie thought that (inefficacious) consciousness set humans apart from animals, T.H. Huxley, arguing from the principle of evolutionary continuity, ascribed consciousness to at least some nonhuman animals as well. But Huxley also argued, with Hodgson, that conscious beings were still conscious automata.
Epiphenomenalism solved half the mind-body problem, by concluding that mind and body do not interact. But the other problem persisted, which is how body gives rise to mind in the first place. Of course, if you don't think that mind is important, this question loses much of its hold. But if you think that mind is important, precisely because it has causal powers, than you can't be an epiphenomenalist, or even a proponent of conscious automata. But if you don't want to be an idealist, or a dualist, then what?
Epiphenomenalism is perfectly captured in one of its earliest expressions, the steamwhistle analogy of T.H. Huxley (1868), Darwin's cousin and known as "Darwin's Bulldog" for his vigorous defense of the theory of evolution by natural selection:
The consciousness of brutes would appear to be related to the mechanism of their body simply as a collateral product of its working, and to be completely without any power of modifying that working as the steamwhistle which accompanies the work of a locomotive engine is without influence upon its machinery.
Note, however, that Huxley refers
to "the consciousness of brutes" (emphasis added).
For all that he and Darwin believed about evolutionary
continuity, he still seemed to believe that there was
something special about the consciousness of humans
--to wit, that it might indeed play a causal role in behavior.
However, even epiphenomenalism acknowledges consciousness -- it just thinks it's epiphenomenal. So even epiphenomenalism can't escape what the philosopher Joseph Levine calls the explanatory gap. Levine argued that purely materialist theories of mind, which rely solely on anatomy and physiology, cannot, in principle, explain how the physical properties of the nervous system give rise to phenomenal experience. To illustrate his reasoning, consider the following two physicalist explanations:
In the Principles of Psychology (1890), William James embraced the viewpoint that the purpose of consciousness was to aid the organism's adaptation to its environment. James rejected both the automaton-theory (and epiphenomenalism) and the mind-stuff theory, devoting a chapter of the Principles to each view (James was close friends with Prince, but friendship has its limits). But James himself never got beyond Descartes' impasse. Convinced as a scientist that materialism was right, but also convinced as a human being that mind had causal efficacy, James ended up adopting a variant of psychophysical parallelism - that there was a total correspondence of mind states with brain states, but that empirical science can't say more than that. James considered this stance to reflect an intellectual defeat, and he simply resigned himself to it and to the Cartesian impasse (did I mention that James was chronically depressed?).
James's resignation is echoed in some quarters of contemporary philosophy in a doctrine that has come to be known as Mysterianism, so named by the philosopher Owen Flanagan after the 1960s one-hit rock group "Question Mark and the Mysterians" (their one hit was "96 Tears", which was originally supposed to be titled "69 Tears" until someone thought better of it). Mysterianism holds that consciousness is an unsolvable mystery, and that the mind-body problem will remain unsolvable so long as consciousness remains in the picture.
An early version of modern Mysterianism was asserted by the philosopher Thomas Nagel, in his famous 1979 "Bat" essay, which was really an argument that consciousness is not susceptible to analytic reduction:
"[T]his... subjective character of experience... is not captured by any of the familiar, recently devised reductive analyses of the mental, for all of them are logically compatible with its absence. It is not analyzable in terms of any explanatory system of functional states, or intentional states, since these could be ascribed to robots or automata that behaved like people through they experienced nothing."
Now, on the surface, this could simply be taken as a statement of dualism. But recall that Nagel's essay began on a note of despair that the mind-body problem is soluble at all (emphasis added):
"Consciousness is what makes the mind-body problem really intractable. Without consciousness, the mind-body problem would be much less interesting. With consciousness, it seems hopeless."
A more recent version of Mysterianism was outlined by the philosopher Colin McGinn (1989, 2000), who assumes that materialism is true, but asserts that we are simply not capable of understanding the connection between mind and body -- in his term, gaining cognitive closure on this issue:
We have been trying for a long time to solve the mind-body problem. It has stubbornly resisted our best efforts. The mystery persists. I think the time has come to admit candidly that we cannot resolve the mystery.... [W]e know that brains are the de facto causal basis for consciousness, [but] we are cut off by our very cognitive constitution from achieving a conception of... the psychophysical link.
Whereas James thought that the mind-body problem was a more-or-less temporary failure of empirical science, McGinn argues that the mind-body problem is insoluble in principle, because we simply lack the cognitive capacity to solve it -- to achieve what he calls cognitive closure on the problem.
McGinn draws an analogy between the limits of psychological knowledge and Piaget's theory of cognitive development. In Piaget's view, a child at the sensory-motor or preoperational stage of cognitive development simply cannot solve certain problems that can be solved by children at the stages of concrete or formal operations. He implies that if there were a fifth stage of cognitive development, or maybe a sixth or seventh, maybe we could get closure on the mind-body problem. But since there are inherent limitations on our cognitive powers, we can't.
A Post-Operational Stage of Thought?
Actually, there just might be a post-operational stage, or stages. Piaget's theory implies that the various stages of cognitive development can only be known from the standpoint of a higher stage. So if Piaget was able to identify a stage of formal operations, that implies that somebody -- Piaget himself, at least! -- must be at yet a higher stage of cognitive development. Call this Stage 5. But even Piaget never claimed to have solved the mind-body problem, so if McGinn is right then cognitive closure will have to wait until somebody gets to a sixth or higher stage.
In fact, the promise of such higher stages of cognitive development is made explicit by the Transcendental Meditation (TM) movement founded by the Maharishi Mahesh Yogi. One of the Maharishi's followers, the late psychologist Charles N. ("Skip") Alexander, drew explicit parallels between Maharishi's stage theory of consciousness and Piaget's stage theory of cognitive development. And, in fact, TM holds out the promise of achieving through meditative discipline a union of mind and body -- from which standpoint, presumably, the solution to the mind-body problem will be clear. See, for example, Higher Stages of Human Development: Perspectives on Adult Growth, ed. by Alexander and E.J. Langer (Oxford University Press. 1990).
McGinn hastens to point out that psychology is not alone, among the sciences, in lacking cognitive closure on some problem. Physics and mathematics are the most advanced (and arguably the most fundamental) of the sciences, but physicists labor under the implications of Heisenberg's uncertainty principle, and mathematicians suffer from Godel's incompleteness theorem. Still, physicists and mathematicians manage to get a lot of work done, solving other problems, and that's what psychologists and philosophers should do too.
In other words: if the mind-body problem is insoluble, we should just get over it.
Although set aside by James in the latter part of the 19th century, and by the Mysterians in the latter part of the 20th century, the mind-body problem has continued to incite effort in the 20th and now the 21st centuries, including the widespread embrace of materialist monism but even a revival of dualism. But first it had to go through a stage where the mind-body problem itself was simply rejected.
That was what behaviorism was all about. These philosophers and psychologists effectively solved the mind-body problem by rejecting it, and they did this by rejecting the mind as a proper subject-matter for science.
Within psychology, the seminal documents of the behaviorist revolution are by John B. Watson:
Watson's behaviorism was a reaction to both structuralism and functionalism in the new scientific psychology. To Watson (and he was not alone), introspection seemed to be getting the field nowhere, and had become bogged down in disputes over such issues as whether there could be imageless thought. Watson himself also hated serving as an introspective observer. Watson himself had been trained as a functionalist at Chicago, and had conducted a successful line of research on animal learning, but he balked at the functionalists' attribution of consciousness to nonhuman animals.
Watson's central assertions were as
Consciousness is simply irrelevant to this program, because consciousness has nothing to do with behavior. New behaviors are acquired as a result of learning (construed as the conditioning of reflexes), and individual differences in behavior are the result of individual differences in learning experiences. Watson's emphasis on learning is exemplified by Watson's dictum :
Give me a dozen healthy infants, well formed, and my own specified world to bring them up in and I'll guarantee to take any one at random and train him to become any type of specialist I might select -- doctor, lawyer, artist, merchant-chief, and yes, even beggar-man and thief, regardless of his talents, penchants, tendencies, abilities, vocations, and race of his ancestors.
Watson left psychology in 1920, when he was fired from his faculty position at Johns Hopkins in the midst of a messy divorce scandal involving his relationship with a graduate student. Eventually Watson found work as the resident psychologist at J. Walter Thompson, the famous advertising agency, in which capacity he invented the "coffee break" as part of a campaign for Maxwell House coffee (See? Psychology has practical benefits!). But behaviorism wasn't harmed by this reversal of his personal fortune, and clearly dominated psychological research from the 1920s to the 1960s -- though not in its pure Watsonian form.
In the 1930s, behaviorists moved beyond Watson's "muscle-twitch" psychology, in which behavior was construed as a string of innate and conditioned reflexes closely tied to the structure of the peripheral nervous system, toward an emphasis on molar rather than molecular behavior. In the words of E.B. Holt (1931), what came to be called neobehaviorism was concerned with "what the organism is doing". For example, at Berkeley E.C. Tolman showed that rats who had been trained to run a maze for food would also swim for food if the maze was flooded. The maze was the same, but because running and swimming involved different muscle movements, what had been learned was a molar behavior -- e.g., "get from Point A to Point B" rather than a particular sequence of muscular movements in response to the maze stimulus.
Moreover, many neobehaviorists held more
liberal attitudes than Watson on the role of mental states
Behaviorism in psychology had its parallel in philosophical behaviorism, whose roots in turn were in earlier approaches to the philosophy of mind.
Logical positivism began in the "Vienna
Circle" of philosophers, such as Herbert Feigl and Rudolf
Carnap, and was promoted in England by A.J. Ayer and in
America by Ernest Nagel. Logical positivism is based
on the verification principle, which states that
sentences gain their meaning through an analysis of the
conditions required to determine whether they are true or
false. There are, in turn, two means of verifying the
truth-value of a statement.
Sentences which cannot be empirically verified, either analytically or synthetically, are held to be meaningless. Because statements about people's mental states are empirically unverifiable, the logical positivists held -- or, at least, they strongly suspected -- that any statement about consciousness -- and indeed the whole notion of consciousness itself -- is simply meaningless.
Linguistic philosophy, which arose through the work of Ludwig Wittgenstein, Gilbert Ryle, and J.L. Austin, argued that most problems in philosophy are based on misunderstandings or misuses of language, and that they simply dissolve when we pay attention to how ordinary language is used. Linguistic philosophers placed great emphasis on reference -- the objects in the objective, publicly observable real world to which words refer. Because mental states are essentially private and subjective, linguistic philosophers harbor the suspicion that mental states don't refer to anything at all, and that mental-state terms like "consciousness" are essentially meaningless.
The Ghost in the Machine. While both
logical positivists and linguistic philosophers focused a
great deal of attention on the terms representing mental
states, the philosophical behaviorists, like their
psychological counterparts, tended to dispense with
mental-state terms entirely. For example, in The
Concept of Mind (1949), Gilbert Ryle argued that the
mind is "the ghost in the machine" (a phrase that inspired
the classic rock album by The Police). For Ryle,
the whole mind-body problem reflects what he called a category
mistake -- a mistake in which facts are represented as
belonging to one domain when in fact they belong to
another. With respect to mind and body, the category
mistake comes in two forms:
The bottom line in philosophical behaviorism is that we cannot identify mental states independent of behavioral states and the circumstances in which behavior occurs. This is also essentially the bottom line for psychological behaviorism, to the extent that it talks about mental states at all. Both psychological and philosophical behaviors seek to get around Descartes' impasse by refusing to talk about mind at all.
The hegemony of the behaviorist program within psychology began to fade in the 1950s, with the gradual appreciation that behavior could not be understood in terms of the functional relations among stimulus, response, and reinforcement.
the deep sources of the cognitive revolution lie with some
neobehaviorists who made their careers in the study of animal
learning, but who critiqued salient features of the behaviorist
early anomalous findings were generally ignored or dismissed by
practitioners of behaviorist "normal science", in a manner that
would make Thomas Kuhn proud. But in the 1960s, evidence
for cognitive constraints on learning mounted rapidly:
These and other studies, following on the pioneering research of Tolman and Harlow (and others) made it clear that we cannot understand even the simplest forms of learning and behavior in so-called "lower" animals -- never mind complex learning in humans -- without recourse to "mentalistic" constructions such as predictability, controllability, surprise, and attention. Although the cognitive revolution was chiefly fomented by theorists who were interested in problems of human perception, attention, memory, and problem-solving, the results of these animal studies increased the field's dissatisfaction with the dominant behaviorist paradigm, and increased support for the cognitive revolution in psychology.
cognitive revolution was also fostered by the development of the
high-speed computer, which could serve as a model, or at least a
metaphor, of the human mind:
Put concisely, the computer model of the mind showed how a physical system could, in some sense, "think" by acquiring, storing, transforming (i.e., computing) and using information. In some respects, the computer metaphor solved the mind-body problem in favor of materialism, because it showed how a physical system could operate something like the mind. But the fact that computers could "think" (or at least process information) raised the question of whether computers were, or could be, conscious. Put another way, the fact that computers could "think" without being conscious suggested that maybe consciousness was epiphenomenal after all. In any event, the fact that psychological discourse was re-opened to mental terms revived discussion of the mind-body problem, and promptly stuck us right back in the middle of Descartes' impasse -- exactly where William James had left us in 1890!
One difference between the beginning of the 21st century and the end of the 19th is that not too many cognitive scientists seriously entertain dualism as a solution to the mind-body problem. Almost everybody adopts some form of the materialist stance, for the same reason that James did -- because we understand clearly that mental states are somehow related to states of the brain. At the same time, many people remain closet dualists, for reasons articulated earlier: religious belief, the persistence of folk psychology, or disciplinary commitment to the psychological level of analysis (that's my excuse!). Others, however, have gotten beyond what they see as irrationality, sentimentality, or ideology to proliferate a variety of "new" materialisms -- or, at least, more precise statements of materialist doctrine.
Modern versions of materialism are based on one or another version of identity theory, which holds that mental states are identical to brain states. This position is distinct from epiphenomenalism, which holds that mental states are the effects of brain states; and it is also distinct from psychophysical parallelism, which holds merely that mental states are correlated with brain states.
theory comes in two forms:
Types, Tokens, and Categories
The type and token versions of identity theory are named by analogy to the type-token difference in categorization. In categorization, type is the category (e.g., undergraduate class), while token is a particular instance of that category (e.g., Psychology 129 as taught in the Spring Semester of 2005.
between the two versions of identity theory has
important implications for scientific research.
Many traditional cognitive scientists prefer token identity theories, which have the benefit of allowing mental talk and folk psychology to remain legitimate discourse. But some cognitive scientists seem to prefer type identity theories, and seek to abandon mental talk as soon as neuroscience permits.
The distinction between type and token identity theories has important implications for the neuroscientific effort to identify the neural correlates of conscious mental states. Consider how these experiments are done.
Note that this methodology assumes type identity -- that every brain that is performing a particular task is in the same state as every other brain that is performing that same task. Otherwise, it wouldn't make any sense to average across subjects. If token identity were true, and every individual brain were in a different state when performing the same task, then the activities of the several individual brains would cancel each other out, and the researcher would be left with nothing but noise. But the signal -- the brain signature -- emerges only when you average across individuals.
If researchers believed in token identity, they'd go about their studies in a very different way. They'd scan a single individual, on many occasions, and average across trials but not individuals to identify the brain signal, and then conclude that some particular part of the brain is active when this particular individual is performing this particular task. But who cares about particular individuals? Nobody -- not at this level of analysis, at least. The goal of cognitive neuroscience is to obtain generalizable knowledge about the relations between brain activity and cognitive processes. Which is why cognitive neuroscientists average across subjects, not just across trials within subjects -- which shows that they embrace a type identity view of mind-brain relations after all.
It turns out that when you talk about mind and body, Leibniz' Law isn't necessarily upheld:
the materialist position has many current adherents, especially
among those who wish to abandon folk psychology -- for example.
Of course, eliminative materialism is a program of reductionism -- specifically, eliminative reductionism, entailing the view that the laws of mental life discovered by psychology can (and should) be reduced to the laws of biological life discovered by biology -- and, presumably, thereafter to the laws of physics. The implication of reductionism is that physics is the fundamental science, and everything else is just nonscientific "folk" talk, to be eliminated as soon as science allows. As the physicist Ernest Rutherford once put it:
Never mind that Rutherford got the Nobel Prize in chemistry. He regarded himself as a physicist, and is generally regarded as the father of nuclear physics.
such a position is unpalatable to anyone but physicists and
those possessed of physics-envy (and perhaps
philatelists). Partly for that reason, the Churchlands,
Patricia and Paul, have argued (together and separately) for a
program of intertheoretic reductionism, which promises to
preserve the legitimacy of the psychological level of
"the real-world findings of neuroscience".
The clear implication is, that mental states aren't real, and that psychology, as the science of mental life, doesn't have anything to do with the real world.
Note that it never occurs to them that neuroscience should be grounded in the real-world findings of psychology, which would be the case if they were really interested in the symbiotic relations between two theories, or two levels of analysis. The clear implication of their work is that the only "real world" is the world of neuroscience. The world of neuroscience can be objectively described, while the world of mind and consciousness is the world of ether, phlogiston, and fairies.
You get a sense of what eliminative reductionism is all about when, as quoted in a New Yorker article on their views, Pat says to Paul, after a particularly hard day at the office,
"Paul, don't speak to me, my serotonin levels have hit bottom, my brain is awash in glucosteroids, my blood vessels are full of adrenaline, and if it weren't for my endogenous opiates I'd have driven the car into a tree on the way home. My dopamine levels need lifting. Pour me a Chardonnay, and I'll be down in a minute" (as quoted by MacFarquhar, 2007, p. 69),
It's funny, until you stop to reflect on the fact that these people are serious, and that their students have taken to talking like this too.
But really, when you step back, you realize that this is just an exercise in translation, not much different in principle from rendering English into French -- except it's not as effective. You'd have no idea what Pat was talking about if you didn't already know something about the correlation between serotonin and depression, between adrenaline and arousal, between endogenous opiates and pain relief, and between dopamine and reward. But is it really her serotonin levels that are low, or is it her norepinephrine levels -- and if it's serotonin, how does she know? Does she have a serotonin meter in her head?
Only by translating her feelings of depression into a language of presumed biochemical causation -- a language that is understood only by those, like Paul, who already have the secret decoder ring.
And even then, the translation isn't very reliable. We know about adrenalin and arousal, but is Pat preparing for fight-or-flight (Cannon, 1932), or tend-and-befriend (S. E. Taylor, 2006)? Is she getting pain relief or positive pleasure from those endogenous opiates? And after going through the first five screens of a Google search, I still couldn't figure out whether Pat's glucosteroids were generating muscle activity, reducing bone inflammation, or increasing the pressure in her eyeballs.
And note that even Pat and Paul can't carry it off. What's all this about "talk" and "Chardonnay"? What's missing here is any sense of meaning -- and, specifically, of the meaning of this social interaction. Why doesn't Pat pour her own drink? Why Chardonnay instead of Sauvignon Blanc -- or, for that matter, Two-Buck Chuck? For all her brain cares, she might just as well mainline ethanol in a bag of saline solution. and, for that matter, why is she talking to Paul at all? Why doesn't she just give him a bolus of oxytocin? But no: What she really wants is for her husband to care enough about her to fix her a drink -- not an East Coast martini but a varietal wine that almost defines California living -- and give her some space -- another stereotypically Californian request -- to wind down. That's what the social interaction is all about; and this is entirely missing from the eliminative materialist reduction.
problem is that you can't reduce the mental and the social to
the neural without leaving something crucial out -- namely, the
mental (and the social). And when you leave out the mental and
the social, you've just kissed psychology (and the rest of the
social sciences) good-bye. That is because psychology isn't just
positioned between the biological sciences and the
social sciences. Psychology is both a biological science
and a social science. That is part of its beauty and it is part
of its tension.
In her recent memoir, entitled Touching a Nerve (2014), Patricia Churchland writes that she turned from "pure" philosophy to neuroscience when she realized that "if mental processes are actually processes of the brain, then you cannot understand the mind without understanding how the brain works". To which Colin McGinn, reviewing her book in the New York Review of Books, asked why she stopped there. If mental processes are actually processes of the brain, and brain-processes are electrochemical processes, then she should have skipped over the neuroscience and gone straight to physics. And so should everyone else, including historians and literary critics. But if historians and literary critics don't have to be neuroscientists, why is this an obligation for psychologists?
it's possible to be a materialist monist but not a reductionist. This is the
stance that the late
Donald Davidson (another UCB philosopher ) called anomalous
monism (e.g., in "Mental Events", 2001). Davidson agreed that
the world consists only of material entities, thus rejecting Descartes'
substance dualism; and therefore, all events in the world are
physical events. At the same time, Davidson denied that
mental events, such as believing and desiring, could be explained
in purely physical terms. So, his theory is
ontologically materialistic (because the world
consists only of physical entities) but explanatorily
dualistic (because the network of causal relations
is different for mental events than for physical
In fact, the histories of psychology and of neuroscience show exactly the opposite of what the Churchlands discuss. In every case, whether it is concerned with visual perception or with memory or anything else, theoretical developments in neuroscience have followed theoretical developments in psychology, not the other way around.
for example, the amnesic syndrome, as exemplified by patient
H.M., who put us on the road toward understanding the role
of the hippocampus in memory.
But what exactly is that role? The fact is, our
interpretation of the amnesic syndrome, and thus of
hippocampal function, has changed as our conceptual
understanding of memory has changed.
Here, clearly, neuroscientific data hasn't done much constraining: the psychological interpretation of this neurological syndrome, and its implication for cognitive theory, changed almost wantonly, as theoretical fashions changed in psychology, while the neural evidence stayed quite constant.
another example: what might be called The Great Mental
Imagery Debate -- that is, the debate
over the representation of mental imagery -- or, more
broadly, whether there are two distinct forms of knowledge
representation in memory, propositional (verbal) and
So, in the final analysis, neuroscientific evidence was neither necessary nor sufficient to resolve the theoretical dispute over the nature of knowledge representation.
And, of course, interpretation of PET and fMRI brain images requires a correct description of the subject's task at the psychological level of analysis. Without a correct psychological theory in hand, neuroscience can't find out anything about the neural substrates of mental life, because they don't know what the neural substrates are neural substrates of.
someone once put it (unfortunately, not me):
have said (Kihlstrom, 2010):
Other cognitive scientists prefer token identity theories. They don't seek correspondence between mental events and brain events. Instead, they classify mental events in terms of their functional roles and ignore the physical systems in which these functions are implemented. Philosophical functionalism is closely related to psychological and philosophical behaviorism, in that all that matters are the functional relations between inputs and outputs -- what goes on in between doesn't much matter.
This philosophical functionalism lies at the basis of many programs of artificial intelligence (AI), which attempt to devise computer programs that will carry out the same operations as minds. The term was originally coined by John McCarthy (then at MIT, later at Stanford), who also invented LISP, a list-processing language which still serves as the backbone of AI.
Searle has famously distinguished between two views of AI:
Kenneth Mark Colby (1920-2001)
Colby, one of the pioneers of artificial intelligence, was a psychiatrist who graduated from the Yale School of Medicine in 1943, and computer scientist at Stanford and later UCLA. While at Stanford, Colby developed Parry, a computer simulation of paranoia that is sometimes counted as the only computer program to pass the Turing test. After leaving UCLA, Colby founded Malibu Artificial Intelligence Works, and produced a conversational therapy program called Overcoming Depression.
Parry was adapted from Eliza, a program developed by Joseph Weizenbaum at MIT that was the first conversational computer program, and simulated the interaction between a psychotherapy patient and a "Rogerian" (as opposed to a Freudian) psychotherapist (Eliza was named for Eliza Doolittle, the central character in George Bernard Shaw's play, Pygmalion, which was in turn the basis for the Broadway musical My Fair Lady). According to Colby's New York Times obituary, Parry and Eliza once had a chat, part of which went like this:
For an engaging account of the Turing Test, and the Loebner Prize awarded annually to the "Most Human Computer", see the Most Human Human: What Talking with Computers Teaches Us About What It Means to Be Alive by Brian Christian (2011). It turns out that there's also a prize for the "Most Human Human", and Christian's book charts his quest to win it.
Although I agree with Searle, I believe it is important to distinguish yet another form of artificial intelligence. What I call Pure AI is not concerned with psychological theories or mental states at all, but only with the task of getting machines to carry out "intelligent" behaviors. Most robotics take this form. So does most work on chess-playing by machine. Deep Blue, the IBM-produced program that beat Garry Kasparov, the reigning world champion, in 1997, is a really good chess player, but nobody claims that it plays chess the same way that humans do (in fact, we know it doesn't), and nobody claims that it "knows" it is playing chess. It is just programmed with the rules of the game and the capacity to perform incredibly fast information-processing operations. For pure AI, programs are programs.
Kasparov, commenting on his loss, and on chess as a goal for artificial intelligence research, writes:
The AI crowd... was pleased with the result and the attention, but dismayed by the fact that Deep Blue was hardly what their predecessors had imagined decades earlier when they dreamed of creating a machine to defeat the world chess champion. Instead of a computer that thought and played chess like a human, with human creativity and intuition, they got one that played like a machine, systematically evaluating 200 million possible moves on the chess board per second and winning with brute number-crunching force. As Igor Alexander, a British AI and neural networks pioneer, explained in his 2000 book, How to Build a Mind:
By the mid-1990s the number of people with some experience of using computers was many orders of magnitude greater than in the 1960s. In the Kasparov defeat they recognized that here was a great triumph for programmers, but not one that may compete with the human intelligence that helps us to lead our lives.
It was an impressive achievement, of course, and a human achievement by the members of the IBM team, but Deep Blue was only intelligent the way your programmable alarm clock is intelligent. Not that losing to a $10 million alarm clock made me feel any better ("The Chess Master and the Computer" by Garry Kasparov, reviewing Chess Metaphors: Artificial Intelligence and the Human Mind by Diego Rasskin-Gutman, New York Review of Books, 02/11/2010).
In 2009, computer scientists at IBM announced Watson (named after the firm's founder, Thomas J. Watson, Sr., not John B. Watson, the behaviorist), based on the company's Blue Gene supercomputer, intended to answer questions on "Jeopardy!", the long-running television game show If successful, Watson would represent a considerable advance over Deep Blue, because, as noted in a New York Times article, "chess is a game of limits, with pieces that have clearly defined powers. 'Jeopardy!' requires a program with the suppleness to weigh an almost infinite range of relationships and to make subtle comparisons and interpretations. The software must interact with humans on their own terms, and fast.... The system must be able to deal with analogies, puns, double entendres, and relationships like size and location, all at lightning speed" ("IBM Computer Program to Take On 'Jeopardy!'" by John Markoff, 04/27/2009).
The IBM Jeopardy Challenge was taped in January and aired on February 14-16, 2011 (the first game of the two-day match was spread out over two days, to allow for presentations on how Watson worked). It pitted Watson against Ken Jennings, who made a record 74 consecutive appearances on the show in in 2004-5, and Brad Rutter, who won a record $3.3 million in regular and tournament play. In a practice round reported in January, 2011, Watson beat them both, winning $4,400 compared to Jennings' $3,400 and Rutter's $1,200. In the actual contest, Watson won again, $77,147 against Jennings' $24,000 and Rutter's $21,600. The machine made only two mistakes: responding "Toronto" to a question about U.S. cities (you could see the IBM executives' jaws drop open), and repeating one of Rutter's incorrect responses.
In addition to his linguistic skills, fund of knowledge and rapid access to it, Watson may have had a slight advantage in reaction time, though. Milliseconds count in Jeopardy, and if so it would be interesting to see a re-run of the contest with Watson constrained to something like humans' average response latencies.
contest, Watson displayed a remarkable ability to parse language
and retrieve information.
In a later match, however, Watson was beaten by Rep. Rush Holt (D.-N.J.), who had been a physicist before being elected to Congress ("Congressman Beats Watson" by Steve Lohr, New York Times, 03/14/2011). One category that Watson failed in was "Presidential rhymes" (as in "Herbert's military operations": What were Hoover's maneuvers?"). So Watson's not invincible (the machine had won only 71% of its preliminary matches, before the televised contest). The point is not that Watson is always right, or that he wins all the time, or that he doesn't win all the time. The point is that Watson is a pretty good question-answering machine.
It is not clear what kind of AI Watson represents. Probably not Strong AI: nobody claims that Watson will "think", and the newspaper article uses the word "understand" in quotes. Many of the principles undergirding Watson's software are based on studies of human cognition, which suggests that it is not Pure AI either, and might be a version of Weak AI. IBM engineers, interviewed after the Challenge was completed, were reluctant to claim that Watson mimicked human thought processes (see "on 'Jeopardy!', Computer win Is All but Trivial" by John Markoff, and "First Came the Machine That Defeated a Chess Champion" by Dylan Loeb McClain, New York Times, 02/17/2011). Watson's performance on pre-Challenge test runs is described by Stephen Baker in "Can A Computer Win on 'Jeopardy'?", Wall Street Journal, 02/05-06/2011).
David Gelertner, professor of computer science at Yale (and victim of the Unabomber), wrote ("Coming Next: A Supercomputer Saves Your Life", Wall Street Journal, 02/05-06/2011):
Watson is nowhere near passing the Turing test -- the famous benchmark proposed by Alan Turing in 1950, in which a program demonstrates its intelligence by duping a human being, in the course of conversation over the Web or some other network, into believing that it's human and not software.
But when a program does pass the Turing test, it's likely to resemble a gigantic Watson. It will know lots about the superficial structure of language and conversation. It won't bother with such hard topics as meaning or consciousness. Watson is one giant leap for technology, one small step for the science of mind. But this giant leap is a major milestone in AI history.
Which strengthens the case for Pure AI. But even if it had been only remotely successful, instead of spectacularly successful, the article notes that it will be a "great leap forward" in "building machines that can understand language and interact with humans". For example, IBM is using an improved version of Watson's technology to develop a language-based interactive system for medical diagnosis.
Will Watson play again? Probably not. Deep Blue never played chess again after defeating Kasparov (part of him is on display in the Smithsonian). He's made his point, it's unlikely that any human will beat him when Jennings and Rutter couldn't, and Watson may have a slight mechanical advantage in reaction time at the buzzer.
So let's give David Ferucci, who led the IBM development team, the last word (quoted in Markoff's 2011 article):
People ask me if this is HAL [the computer that ran amok in 2001: A Space Odyssey]. HAL's not the focus, the focus is on the computer on Star Trek, where you have this intelligence information seek[ing] dialog, where you can ask follow-up questions and the computer can look at all the evidence and tries to ask follow-up questions. That's very cool.
The Two Functionalisms: A Confusion
Watson's behaviorism, has close ties to philosophical functionalism as well as to philosophical behaviorism. So why did I write earlier that Watson was as much opposed to functionalism as he was to structuralism? Because Watson was opposed to a different functionalism. Philosophical functionalism hadn't even been thought of when Watson was writing in the 1910s (neither had philosophical behaviorism, for that matter).
The "school" in psychology known as functionalism was skeptical of the claims made by members of another "school", structuralism, claim that we can understand mind in the abstract. Based on Charles Darwin's (1809-1882) theory of evolution, which argued that biological forms are adapted to their use, the functionalists focused instead on what the mind does, and how it works. While the structuralists emphasized the analysis of complex mental contents into their constituent elements, the functionalists were more interested in mental operations and their behavioral consequences. Prominent functionalists were:
functionalist point of view can be summarized in four
Psychological functionalism is often called "Chicago functionalism", because its intellectual base was at the University of Chicago, where both Dewey and Angell were on the faculty (functionalism also prevailed at Columbia University). It is to be distinguished from the functionalist theories of mind associated with some modern approaches to artificial intelligence (e.g., the work of Daniel Dennett, a philosopher at Tufts University), which describe mental processes in terms of the logical and computational functions that relate sensory inputs to behavioral outputs.
At the turn of the 21st century, theories of mind and body are fairly represented by the various books reviewed by John Searle in The Mystery of Consciousness (1997, reprinting several of Searle's review articles in the New York Review of Books), by the replies of the books' authors, and by Searle's rejoinders. On first glance, most theorists appear to adopt some version of materialism, holding to the view that consciousness is something that the brain does.
This is true even for Searle, who while a vigorous critic of the books under review nonetheless asserts that consciousness is a causal property of the brain (see The Rediscovery of the Mind, 1992).
For Searle, consciousness emerges at certain levels of anatomical organization. Certainly, the human brain, with its billions and billions (apologies to Carl Sagan) of neurons, and umpteen bazillions of interconnections among them, has the complexity to generate consciousness. This is probably true of the brains of nonhuman primates, which also have lots of neurons and neural connections. It may also be true for dogs and cats (certainly Searle holds that his dog Ludwig is conscious). It may not be true of snails, because they may not have enough neurons and interconnections to support (much) consciousness. It's not true of paramecia, because they don't have any neurons at all.
And it's certainly not true of thermostats. Although some computers might be conscious, if they had enough information-processing units and interconnections, by and large Searle is deeply skeptical of any claim that consciousness can be a causal property of anything other than a brain. Rather than calling himself a materialist, Searle prefers to label his view biological naturalism. Brains produce consciousness, even if silicon chips (and beer cans tied together by string) don't.
But it's not just possessing neurons that's important for consciousness. Anatomy alone isn't decisive. General anesthesia, concussion, and coma render people unconscious, but they don't alter the structure of the nervous system. However, they do alter physiology: how the various structures in the nervous system operate and relate to each other.
Although his biological naturalism is closely related to materialism, Searle strenuously opposes eliminative materialism and other forms of reductionism. For him, consciousness cannot be eliminated from scientific discourse because objective, third-person descriptions of brain processes necessarily leave out the first-person subjectivity that lies at the core of phenomenal experience. First and foremost, consciousness entails first-person subjectivity. This cannot be reduced to brain-processes because any third-person description of brain-processes must necessarily leave out first-person subjectivity. For that reason, every attempt to reduce consciousness to something else must fail, because every reduction leaves out a defining property of the thing being reduced -- in this case, the first-person subjectivity of consciousness. (In making this argument, Searle is basically applying Leibniz's Law.)
believes that first-person subjectivity is an irreducible
quality of consciousness, and that this irreducible quality is
produced as a natural consequence of human (and probably some
nonhuman) brain processes, but he has no idea how the brain
actually does it. But, he says, that's not a philosophical
problem. The philosopher's job is to determine what
consciousness is; once that's done, the problem can be "kicked
upstairs" to the neurobiologists, whose job it is to figure out
how the brain does it (Searle makes the same argument about free
is very critical of some of his colleagues, but he takes as
good as he dishes out. In some ways it is unfortunate
that Searle did not include reviews of his own work in The
Mystery of Consciousness, and further exchanges with the
reviewers. Two reviews stand out in particular:
"In the end, Lakoff and Johnson fail in much the same way that Searle does. For just as the debunker needs a little bit of the visionary in him -- enough to leave us feeling that philosophy is worth debunking -- so too does the visionary need a keen instinct for what the debunkers will have to say in response.... The battle between visionaries and debunkers is most fascinating when it takes place within the mind of one individual" (p. 90).
The only way out of this problem, it would seem, is to deny the reality of consciousness -- to say that phenomenal awareness is something that does not really exist, that it is literally an illusion. Or, at least, to say that to the extent that consciousness does exist, it is irrelevant to behavior: That is, consciousness plays no role in the operation of a virtual machine -- a software program that processes stimulus inputs and generates appropriate response outputs, just like a real machine would (which is what computational functionalists think the mind is).
This variant on functionalism appears to be Dennett's position in Consciousness Explained (1991). According to his "Multiple Drafts" theory of consciousness, qualia are things that just happen to happen while stimulus information is being processed from the environment and responses being generated to them. And intentionality doesn't exist either -- it's just a rhetorical "stance" we take when we talk about mind and behavior (Dennett also wrote a book entitled The Intentional Stance).
reduction fails, as Searle says it does, then the only way out
for a materialist is to deny the reality of consciousness. For
Dennett, consciousness is literally an illusion, only one of
many "multiple drafts" of phenomenology, and plays no role in
the operation of a virtual machine. For Dennett, only
behavior matters, and only behavior actually exists.
Conscious mental states don't have any special significance, and
they don't play any causal role in what is going on. For
Dennett, it's behavior that matters, not phenomenology,
Those who recognize in Dennett the earlier arguments of John B. Watson are onto something. For Dennett, the evidence for consciousness is to be found in behavior. First-person subjectivity doesn't count because it's an illusion -- just one of many "multiple drafts" of phenomenology, none of which have any causal impact on behavior or the world.
Dennett's work is especially provocative for his reconstrual of what might be called the zombie bugaboo. Philosophical discussions of consciousness often invoke the notion of zombies, defined as molecule-for-molecule replicas of humans, who can do all the things that humans do except that they do them unconsciously. Thus, consciousness ostensibly differentiates humans from zombies. But for Dennett, we're zombies too -- not because we're unconscious, but because zombies are conscious too. From his perspective of radical functionalism, because their behavioral functions are indistinguishable from that of humans, zombies must have the same internal states as humans, including internal states of consciousness. If we're conscious, so are they. We're all zombies now.
recently reafirmed his views in From Bacteria to Bach and
Back: The Evolution of Minds (2017; given a surprisingly
even-handed review by Thomas Nagel in "Is Consciousness an
Ilusion?", New York Review of Books, 03/09/2017).
Dennett, of course, says "yes" (Nagel, of course, would insist
"No", which is why the tone of the review is so
surprising. Maybe Nagel got tired of fighting).
Adopting terms introduced by Wilfrid Sellars, a British
philosopher, Dennet argues that there is a "manifest image"
of the world as it appers to us, and there is a "scientific
image" of the world consisting solely of particles in
fields of force. The scientific image is real; the
manifest image is literally an illusion. And it's the
manifest image that we're consciously aware of. The
manifest image is a "user-illusion designed by evolution
to fit the needs of its users". And so is
consciousness. Dennett claims that our competence,
or our ability to operate adaptively in the world, does not
depend on our ability to comprehend what we are doing -- just
like a computer (here Dennett invokes the Turing machine) can
competently perform calculations without having any idea what it
is doing. But wait: if consciousness is a user-illusion
designed by evolution, what are the user's "needs" that it
serves? For Dennett, consciousness allows us to monitor
ourselves, and deal with other people. The widely shared
illusion of consciousness allows us to predict each other's
behavior, as well as our own. But consciousness doesn't
play any causal role in this behavior. It's an
afterthought. It's an illusion.
For Dennett, first-person experience has no particular authority, and our attributions concerning our own behavior have no privileged status over other people's attributions. They're just opinions:
Curiously, then, our first person point of view of our own minds is not so different from our second-person point of view of others' minds: we don't see, or hear, or feel, the complicated neural machinery churning away in our brains but have to settle for an interpreted, digested version, a user-illusion that is so familiar to us that we take it not just for reality but also for the most indubitable and intimately known reality of all.
About which Nagel concludes:
About the true nature of the human mind, Dennett is on one side of an old argument that goes back to Descartes. He pays tribute to Descartes, citing the power of what he calls "Cartesian gravity", the pull of the first-person point of view; and he calls the allegedly illusory realm of consciousness the "Cartesian Theater". The argument will no doubt go on for a long time, and the only way to advance understanding is for the participants to develop and defend their rival conceptions as fully as possible -- as Dennett has done. Even those who find the overall view unbelievable will find much to interest them in this book.
of Dennett by Joshua Rothman focuses on Dennett's personal life,
as well as his ongoing debate with David Chalmers New ("A
Science of the Soul", New Yorker, 03/27/2017; UCB's
Terrence Deacon also makes a cameo appearance). . As an
undergraduate at Harvard, Dennett studied with the philosopher
W.V.O. Quine (recall, from the lectures on "Introspection",
Dennett's essay on "Quining Qualia"). His dissertation
advisor at Oxford was Gilbert Ryle, whose famous book about the
mind was entitled The Ghost in the Machine
A wonderful detail: Dennett, a talented wood-carver (and many
other things, beside) fashioned a Russian "maryoshka" nested
doll of Descartes; open up Descartes, and you find a ghost
inside; inside the ghost, you find a robot. That pretty
much captures Dennett's view.
Link to a TED talk by
In the contemporary scene, materialism dominates discussions of consciousness, as arguments rage about whether materialism offers the correct approach to the mind-body problem, and if so which version of materialism is the correct one. But materialism doesn't exhaust the possibilities, and dualism has been revived as well.
example, Karl Popper, the distinguished philosopher of science,
and Sir John Eccles, the Nobel laureate in medicine (who I think
is largely responsible for this work) have proposed a
tri-aspect interactionism which distinguishes among three
According to P&E, World 3 is governed by normative principles such as the rules of logic, literary and musical forms (such as the sonnet and the sonata). These principles are objectively valid, regardless of whether anyone follows them. But, they argue, no physical system in World 1 can appreciate the rules of World 3. Therefore, World 2 is needed as an intermediary -- something that understands the content of World 3 and can apply that understanding in World 1. Because World 2 must be substantially different from World 1, P&E essentially argue for dualism -- the world of the mind is different from the world of the body.
In arguing against materialism, and for a substantial (no pun intended) difference between mind and body, Popper and Eccles have argued for a dualism that matches our introspections: mental states are not the same as physical states, yet mental states can affect the physical world. Yet it's not clear that Popper & Eccles have cleared Descartes' impasse. In fact, they may have made the situation worse, by giving us three worlds to worry about instead of just two!
And, in fact, there may well be a third world to worry about. Many prominent mathematicians consider the laws of mathematics to be genuine discoveries, not mere products, of the mind -- in other words, even though lacking physical reality, they exist independently of mental activity, somewhat along the lines of Plato's forms. Among these theorists is UCB's own Prof. Edward Frenkel, legendary instructor of a lower-division course in multivariable calculus,as represented in his book, Love and Math: The Heart of Hidden Reality (2013). As summarized by Jim Holt ("A Mathematical Romance", New York Review of Books, 12/05/2013):
"How can it be," Einstein asked in wonderment, "that mathematics, being after all a product of human thought independent of experience, is so admirably appropriate to the objects of reality?" Frenkel's take on this is very different from Einstein's. For Frenkel, mathematical structures are among the "objects of reality"; they are very bit as real as anything in the physical or mental world. Moreover, they are not the product of human thought; rather, they exist timelessly, in a Platonic realm of their own, waiting to be discovered by mathematicians. The conviction that mathematics has a reality that transcends the human mind is not uncommon among its practitioners, especially great ones like Frenkel and [Robert] Langlands, Sir Roger Penrose and Kurt Godel. It derives from the way that strange patterns and correspondences unexpectedly emerge, hinting at something hidden and mysterious. Who put those patterns there? They certainly don't seem to be of our making.More recently, another philosopher, T.M. Scanlon has also suggested that certain objects exist "outside of space and time", not part of the material world (Being Realistic About Reasons, 2014). different from the one covered by the natural sciences.
Scanlon argues that normative reasons are not simply derived from
something else, like a person's attitudes or desires that might
justify his behavior. In fact, the driver's behavior is
justified by appeal to something that exists independent of his or
anyone's attitudes. This "something" is a normative
reason. (For an exposition of Sanlon's theory, see
"Listening to Reason" by Thomas Nagel, New York Review of
Normative reasons play a big role in analyses of morality, which
would take us far beyond the scope of this course. My only
point in mentioning Scanlon's work is that Popper and Eccles are
not alone in thinking that there are things which have an
observer-independent existence but which are not part of the
spatially and temporally bounded reality explored by the natural
A rather different take on the problem of consciousness is offered by David Chalmers, in a provocative (and peculiar) blend of materialism and dualism which neither denies that consciousness exists nor reduces consciousness to neural functions. Chalmers' work has been extremely provocative: Alone among the philosophers writing on consciousness, he has inspired a whole book of critical responses, and some people think he's actually solved the mind-body problem. Certainly he does.
Chalmers argues that the easy problems are easy because they concern abilities and functions, such that explanation need only specify the proper mechanism. The hard problem is hard because it remains after all the mechanisms are accounted for, and goes beyond function to experience -- precisely what Levine (1983) called the explanatory gap.
some respects, the distinction between easy and hard
problems is essentially the distinction between "how" and
"why?' questions. Easy questions about structure and
function are questions about How the system is built
and How the system functions. Hard questions
about experience boil down to questions about Why the
system generates consciousness and Why these
functions simply don't transpire in the dark.
For the record, before Chalmers wrote his book, Colin McGinn described consciousness as "the hard nut of the mind-body problem" (1989), and Galen Strawson called it "the hard part of the mind-body problem" (1989). But Chalmers gets credit for formulating the distinction between the easy and hard problems of consciousness, and for articulating just what made "the hard problem" so hard.
If this is true, the next question is whether "Why?" is an appropriate question for science. It seems analogous to questions like "Why is there air?" or "Why are there stars?" -- both of which seem way too metaphysical for science.
In fact, science answers "why" questions by changing them to "how" questions. Air arises from photosynthesis, and stars are a product of the Big Bang and nuclear fusion.
So, perhaps Chalmers has made an easy question into a hard question by changing the way the question is framed, from how to why. And maybe he answers his own hard question by turning it back into an easy question by reframing it from why to how.
Chalmers asserts that some extra ingredient is needed to close the explanatory gap. Because everything in physical theory is compatible with the absence of consciousness, we need a new fundamental assumption to get conscious experience out of a physical system. Chalmers closes the explanatory gap by proposing that experience itself is a fundamental feature of the physical world, just like mass, space, and time. Specifically, Chalmers proposes that experience is an aspect of information.
information theory, as developed in the 1940s and 1950s by
Claude Shannon at Bell Laboratories, information is defined as
the amount of change that occurs between two states of a
Claude E. Shannon (1916-2001)
Shannon's work on information theory, which identified the bit (binary digit) as the fundamental element in all communication, laid the foundation for modern computer science and communications. In his master's thesis, which has been called the most important one produced in the 20th century, he showed that Boolean logic (which solves problems by manipulating just the symbols 0 and 1) could be implemented by a set of electrical switching circuits. More important, Shannon realized, as he put it, that "a computer is a lot more than an adding machine". Because he realized that 0s and 1s could represent anything, not just numbers, Shannon laid the foundation for artificial intelligence.
After receiving his PhD (from MIT, in 1940), he worked on cryptography for the wartime government, and also AT&T's Bell Laboratories on the problem of noise-free transmission of messages. In this context, he proposed that
(as quoted in "Claude Shannon, Mathematician, Dies at 84" by George Johnson, New York Times, 02/27/01).
In his famous two-part paper, "A Mathematical Theory of Information" (1948), Shannon showed how adding extra bits to a message could keep it from being garbled by noise -- the genesis of contemporary error-correction codes in computer science. Shannon, who moved to MIT in 1958 (he retired in 1978), was one of the world's great eccentric geniuses. He used to ride a unicycle through the halls at Bell Labs, built a computer that could compute in Roman numerals, and developed a mathematical theory of juggling. He suffered from Alzheimer's disease in his last years.
Shannon's highly mathematical theory was rendered into readable English prose by Warren Weaver, and Shannon and Weaver together published a book-length treatment of the theory in 1949.
In his double-aspect
theory of information, Chalmers asserts that information
has a physical aspect (which embodies a difference between one
or more physical states of the world) and an experiential aspect
(which gives rise to consciousness). Thus, information
physically represented in the brain (e.g., by a pattern of
neural firings) naturally gives rise to conscious experience,
because conscious experience is one aspect of the state of being
informative. But human brains aren't the only things that
Although this move might strike some observers
(including myself) as a deus ex machina, Chalmers
insists that everything that embodies information is
conscious, because information always has a dual aspect. Still, he never quite addresses the "hard
question" of just how information translates into
A Deus Ex Machina?
In ancient Greek and Roman drama, when the plot got stuck, or the play had to come to an end, the writer occasionally arranged for an actor, playing a god, to be swung onto stage by a crane-like machine, decide the outcome of the play, and explain what had gone on. Frankly, it's hard to avoid the feeling that Chalmers has done something similar -- the dual-aspect theory of information seems to come out of nowhere, and explains everything just a little too neatly. (Illustration at left from dkimages.)
At the very least, it seems that Chalmers has revived Morton Prince's old "mind-stuff" theory, against which James railed in the Principles, in the modern guise of information theory. If that's what counts as a solution to the mind-body problem, then OK....
A related idea comes from UCB's own Terrence Deacon, a cognitive anthropologist who has long been concerned with the problem of how life, not to mention sentient life, could have evolved from inanimate matter. Deacon offers a solution in Incomplete Nature: How Mind Emerged from Matter (2012). The essential ingredient for life, in his view, is the emergence of a complex system that is teleodynamic -- autonomous, self-maintaining, temporally stable, and resistance to entropy. One such system is the biological cell -- the basic building-block of life. And the brain, of course, is a complex system of cells. Whereas Chalmers believes that consciousness is a property of any physical system that embody information, Deacon suggests a somewhat more restrictive view: that the physical system must consist of biological cells, which have the five properties just listed. Deacon does not quite verge on panpsychism, as Chalmers does, ascribing consciousness to things like computers and thermostats. But he comes close, asserting that there is sentience -- consciousness -- wherever we find self-preserving dynamic systems. That includes brains, but also cells (like individual neurons) and molecules.
But then he edges closer to panpsychism when he asserts that it's not just organic material that can be sentient. Any entity that is self-organizing will have consciousness, precisely because -- you have to forgive the pun here -- it organizes its self. That includes biological matter, of course, but presumably it can also include inorganic matter, like perceptrons. Anyway, Deacon believes that while neurons and the things made of them are conscious, you don't need neurons to be conscious. All you need is a self-organized, autonomous, temporally stable entity that resists entropy. The key to the argument seems to be that, in order to be conscious, you have to have some sort of self, and self-organizing, teleodynamic systems have a self by definition.
Still, when you ask how teleodynamic systems attain consciousness, simply by virtue of being teleodynamic, all that can be said is: "it's not clear".
For a critique of Deacon's ideas, see "Can Anything Emerge from Nothing?" by Colin McGinn, New York Review of Books, 06/07/2012. An exchange of views between Deacon and McGinn was published in the NYRB on 10/11/2012.
Much the same sort of argument seems to be made by
Antonio Damasio, a neurologist who has written frequently on
consciousness and related topics. Damasio focuses on the
essentially subjective nature of consciousness, and notes that,
in order to have subjectivity, or first-person experience, you
have to have a sense of self -- a first person in the first
place!. So, he tries to figure out which parts of the brain are
critical for the sense of self. The general argument of
Damasio's book, Self comes to Mind (2011) goes as
For a critique of
Damasio's ideas, see "The Mystery of Consciousness Continues" by
J.R. Searle, New York Review of Books, 06/09/2011. An
exchange of views with Barclay Martin was published in the NYRB
LInk to a TED talk by
Both Chalmers and Deacon exemplify what might be
considered a search for the "secret sauce" -- an attempt to
identify the one thing that makes the difference
between consciousness and unconsciousness.
Earlier, Koch joined Francis Crick in proposing that the key to consciousness was the synchronized firing of neurons at 40 cycles per second (hertz). Koch subsequently revised his view, stating only that 40-hertz firings were necessary for the formation of integrated percepts.
At roughly the same time, Tononi joined Gerald Edelman in proposing the dynamic core theory of consciousness, which proposed that consciousness is a product of both highly integrated and highly differentiated information (Tononi & Edelman, 1998; Edelman & Tononi, 2000).
More recently, and working both together and separately, Tononi (in "Consciousness as Integrated Information: A Provisional Manifesto, 2008; see also Balduzzi & Tononi, 2008) and Koch (in The Quest for Consciousness, 2004, and Consciousness: Confessions of a Romantic Reductionist, 2012) have refined the dynamic core theory of consciousness in a new information integration theory.
For a review of Koch's 2004 book, see "Consciousness: What We Still Don't Know" by J.R. Searle, New York Review of Books, 01/13/2005; also an exchange between Searle and Stevan Harnad, NYRB 06/23/2005.
For a review of Koch's 2012 book, see "Can Information Theory Explain Consciousness?" by J.R. Searle, New York Review of Books, 01/10/2013; also an exchange between Searle and Koch and Tononi (writing together), NYRB 02/.
Baars, a cognitive neuroscientist who is affiliated with Crick's Neurosciences Institute, has proposed a theory of consciousness known as Global Workspace Theory (GWT; 1988).
GWT holds that the function of consciousness is to combine a number of different cognitive processes into "a single coherent experience". It does this by making the contents of various subordinate, modular information-processing functions available to each other -- so that, for example, we can think about what we're perceiving, remember similar events from the past, and the like. These different flows of information all come together in a global workspace -- hence the name of the theory. This global workspace is, essentially, working memory.
Similarly, Morsella (2005) has proposed a
Supramodular Interaction Theory. Following Fodor's (1983)
doctrine of modularity, Morsella argues that the outputs of
different low-level modules feed into "supramodules" that
perform higher-level tasks, leading to overt behavior executed
by various musculo-skeletal systems. For example, one
module (processing information from a low-level blood-sugar
module) might give rise to feelings of hunger, initiating a
search for food. another supramodule might take
information from the skin senses, generate feelings of pain, and
initiate escape or avoidance behavior. The activities of
these supramodules may conflict, as when the act of eating
causes pain (because the eater has a toothache?). The
function of consciousness, in this view, is facilitate the
resolution of conflict between different musculo-skeletal
systems. He argues that only the skeletal musculature is
controlled by conscious processes -- everything else done by
various effector systems goes on unconsciously. Thus, it
is the phenomenal awareness of conflict between action
tendencies that permits the conflict to be resolved.
One of the most interesting contemporary approaches to the mind-body problem involves a revival of panpsychism -- the idea that consciousness pervades the physical universe. Panpsychism was implied in Morton Prince's notion of mind-stuff, and more explicitly implicated in David Chalmers's idea that consciousness is a property of any information system. Panpsychism was a prominent topic at the 2016 conference on "The Science of Consciousness", and also ran through a series of talks on "The Rise of Human Consciousness" presented at the New York Academy of Sciences on May 23, 2016.
Most prominently, Giulio Tononi (Biological
Bulletin, 2008; Oizumi, Albantakis, & Tononi, PLoS
Computational Biology, 2014), a neuroscientist at the
University of Wisconsin (and former student of Gerald Edelman),
has taken a page from Chalmers's book and proposed an Integrated
Information Theory which holds that consciousness is a
property of any physical system that has the ability to store and
integrate a large amount of information. Tononi has also
proposed a mathematical unit, phi, to measure how much
information integration -- that is, how much consciousness
-- any entity has.
The details of how phi is
calculated are beyond my competence to explicate, so I'm not going
to even try.
Unfortunately, phi has some
problems. Scott Aaronson, a computer scientist, has
calculated that, following Tononi's formula, a DVD player
(technically, a component of a CD player that corrects for errors
induced by flawed media) has more consciousness than a human
brain. Aaronson argues that such a result contradicts our
intuition that, however much consciousness a DVD player has, it
can't have more consciousness than a typical human.
In reply, Tononi noted that Aaronson's calculations depended on an earlier version of the Phi formula -- but then conceded that the latest version, known as Phi 3.0, confirms Aaronson's result, and actually increases the superiority of the DVD player. More important, Tononi isn't bothered by the notion that a DVD player might have consciousness. He points out, correctly, that empirical science has a long and distinguished history of correcting our intuitions about the nature of things. And, in fact, he goes on to assert that an even simpler structure, a sufficiently large 2-dimensional grid of logic gates, when physically implemented, would have a large value of phi -- and, thus, be conscious.
Aaronson, in his rejoinder, calls this
the "Copernicus of Consciousness Argument", after the astronomer
who argued that, despite our intuitions, the sun does not revolve
around the earth. He insists that any formula that indicates
that a "simple expander graph" has consciousness doesn't comport
with common sense. Or, as he puts it "When the clock strikes
13, it's time to fix the clock...".
Aaronson's blogpost, which contains a very math-heavy
explication of phi.
Link to Tononi's reply.
Still, the important point in this
context is that Tononi has seriously proposed that nonliving
matter, including any arbitrary physical system, can be conscious,
so long as it can store and integrate a large amount of
Despite this criticism, Max Tegmark (2015), a cosmologist at MIT (and UC Berkeley PhD), has embraced and expanded IIT. Tegmark actually proposes that consciousness is a state of matter, like solid, liquid, gas, or plasma. He calls it "perceptronium", in homage to Minsky and Papert's perceptrons -- early versions of self-organizing "neural networks" that were capable of learning. Tegmark traces several steps that lie between the usual states of matter and states of consciousness.
Putting all of this together, Tegmark argues that any physical system will have consciousness if it satisfies six - -but really four -- principles.
In some ways, Tegmark's
version of panpsychism is preferable to Chalmers's and Tononi's,
because it puts limits on what can be conscious. As he
writes, clocks and diesel generators tend to exhibit high
autonomy, but lack substantial information storage capacity"
(2015, p. 4). Therefore, they are unlikely to be
conscious. Still, it seems to me that any materialists
theory that has to solve the mind-body problem by invoking a new
substance known as "perceptronium" might just as well cite
Morton Prince and talk about "mind-stuff". It gets us to
pretty much the same place. Which is nowhere.
Issues of panpsychism
aside, Tononi's integrated information theory of consciousness
has inspired the development of a strictly biological measure of
consciousness, which does not rely on either self-report or
behavior, and which can be applied to any species that has a
brain: the Perturbational Complexity Index (PCI;
Massiminii et al., 2005). The general idea behind the PCI
is that conscious processing involves the complex integration of
various areas and systems of the brain, especially in the
thalamocortical system. To obtain a value for PCI, Casali
et al. first deliver a pulse of transcranial magnetic
stimulation (TMS) to the brain: this is the "Zap" of what has
been called Zap and Zip. The the electrical
potentials evoked by this stimulus are recorded by EEG by means
of a dense array of electrodes. These recordings, taken
from various regions of the cerebral cortex, are then aggregated
by an algorithm derived from data-compression techniques (think
zipfiles or MP3s) derived from computer science: this is
the "Zip" of Zap and Zip. To take an analogy:
imagine that a an organ sounds a chord in a great cathedral, and
we measure how long it reverberates, and how the echo reaches,
and is passed around, the various alcoves and chapels that
surround the main nave. PCI is kind of like that.
But there isn't just one "zap". As with event-related
potentials, there are dozens, even hundreds, of zaps. Each
individual subject then receives an aggregate score, ranging
from 0 to 1; the investigator may also record the maximum
individual PCI score, known as PCImax.
In an initial study,
Massimini, Tononi, and their colleagues Tononi and Massimini showed
that PCI could distinguish between waking and sleeping in normal
subjects (Massimini et al., Science, 2005). A
later study showed that PCI could distinguish between subjects
who were awake, asleep (NREM sleep), or anesthetized (by various
agents), as well as brain-injured patients in various stages of
coma (Casali et al., Science Translational Medicine,
2013). A more recent study found that a PCI value of .31
had 100% specificity and sensitivity in discriminating between
subjects who were conscious and those who were unconscious
(i.e., in NREM sleep or anesthetized). That is, 100% of
conscious subjects were identified as conscious were indeed
conscious (including those who were dreaming), and 0% were
unconscious; and 100% of those it identified as having lost
consciousness were indeed unconscious (including those in
dreamless sleep), and 0% were conscious. Applying this
criterion to patients in various stages of coma, PCI
successfully identified all of those who were in the "minimally
conscious state", and suggested that a minority of those
diagnosed as in the "vegetative state" possessed, at least
minimal levels of consciousness. The upshot of all this
work is that Tononi, Massimini, and their colleagues believe
that they have created a biological index of consciousness that
does not rely on either self-reports or behavioral
responsiveness; that that this index is based on Tononi's
Information Integration Theory of consciousness.
There is more on
consciousness in sleep, anesthesia, and various stages of coma
elsewhere in these lectures, where you'll also find further
discussion of the Casali et al. (2016) paper.
For an account of the discovery and implications of PCI, see "How to Make a Consciousness Meter" by Christof Koch, Scientific American, 11/2017. Koch thinks that the PCI will permit us to objectively measure consciousness without relying on self-report. I think he's mistaken, for reasons that will become clearer in the lectures on sleep and dreams.
At the end of this tour, we appear, like James, to be left stranded at Descartes' impasse. As scientists, we must embrace materialism: the mind is what the brain does, and science must be based on public observation. But our experience as conscious beings inclines us toward dualism: the intuition that mental states are different from physical ones, and the belief that mental states have causal efficacy, and the view that there is something about consciousness that is essentially private and subjective.
As a result, philosophers and other cognitive scientists will continue to argue about the mind-body problem.
This situation, where after more than 350 years of hard thought we are pretty much back where we started, suggests that Searle is probably right that the mind-body question has been poorly constructed, and that to make progress we have to break out of received categories of mind and body, dualism and monism, idealism and materialism. We know that the mind is a function of the body: the mind is what the brain does, and our mental capacities are the product of biological evolution. At the same time, dualism has its pleasures. It comports with our experience of ourselves as sentient beings with free will. Psychologists, who are primarily concerned with the nature of mental life, are by their very nature dualists of a sort. Moreover, dualism keeps certain interesting problems alive, such as the problem of free will and the possibility of psychosomatic interactions.
one project for science is to determine how the brain does
it -- that is:
So while some cognitive scientists engage in endless debates over consciousness, functionalism, and reductionism, there are still a number of interesting scientific problems to be solved.
We also know, intuitively, that consciousness has causal efficacy. Our thoughts, feelings, and desires cause us to do what we do, and our mental states can affect bodily states. So another project for science is to find out how the brain does this, too. How do mental states affect bodily states and functions, as in placebo effects and psychosomatic effects. Both projects are materialist in nature, but both projects take mind, and consciousness, seriously -- they don't try to write them out of the picture.It turns out that there is not just one mind-body problem, but at least four. Each aspect of the mind-body problem is taken up in separate lecture supplements:
page last revised 10/27/2017.