NEAR enough 300 years ago, the great Gottfried Leibniz said two interesting things about consciousness. One was that if there were a machine for producing conscious experiences such as perceptions, then even if it were as big as a mill so that we could walk around among the wheels we would find “nothing but pieces which push one against the other and never anything to account for a perception”.
His other remark was by way of rebuke to John Locke. Locke thought that it was just “God’s good pleasure” to “annex” different sensations, such as pain, to various processes of brain and body, such as those caused by a pinprick. Leibniz insisted that it was “not God’s way to act in such an unruly and unreasoned fashion”. Rather the relation between the “motions” that being pricked by a pin produces in the body, and the felt pain, must be open to understanding and reason: in Leibniz’s own analogy, it should be something like the relation between a circle and its projection onto a plane at an angle to it. Stripped of the theological dressing, the point is that we do not understand the relation between mind and body if their connection might as well be pure happenstance, luck or accident, rather than understood necessity.
Part of the interest of Leibniz’s two remarks is that they fit together uncomfortably. If delving into fine physical and neurological detail is not going to explain the emergence of consciousness, as the first remark suggests, then how will we reach the eureka moment that the second remark promises, the illumination when the relationship between brain and consciousness becomes as obvious and open to rational understanding as that between a circle and a projected ellipse? Leibniz seems to have combined a stringent condition on solving the problem with pessimism about our only avenue to satisfying it.
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We have not got brains as big as mills, but we have made up for that by inventing a plethora of tools for discriminating events in the brain at ever-increasing levels of detail. Scientists can locate synaptic connections in space and time, and plot families of pathways between areas of brain activity. Each of the works under review delights in the complexities that are uncovered almost daily. They savour the staggering numbers: 30 billion neurons in the cerebral cortex alone; a million billion synapses. They go on to describe two-way interconnections, simultaneous activations of different areas, as well as the surprising examples of functions taking place without conscious experience at all, as in the famous cases of blindsight, and other clinical surprises. It is tempting to hope that with all these new facts at our disposal, we can prove Leibniz’s pessimism unfounded. Plenty of writings promise us that we can.
The problem of consciousness, if there is one, arises acutely within a framework that almost all scientists and philosophers of mind share. This is the view that all conscious processes, and indeed all mental processes of any kind, are dependent upon the activity of the brain and central nervous system. In modern debates, this is not open to dispute. But within that consensus, there is still the question of just how the dependency works. Are there laws that relate the physical and the mental, and if so, why?
A century ago people talked of “emergence”: mental activity somehow emerged out of brain activity, like Venus popping out of the sea. But that sounds mysterious, little better than René Descartes’ speculation that there was a window between the body and the soul located in the pineal gland. More recent philosophers talk of mental processes as “supervening” on physical processes. Supervenience sounds soothing. It is supposed to be an intelligible version of emergence – Leibniz-friendly emergence, as it were, although not everyone believes it deserves that reputation.
In his 1996 book The Conscious Mind, the philosopher David Chalmers felicitously distinguished between problems of consciousness that might be solved by relatively normal science, and what he called “the hard problem”, the problem that bothered Locke and Leibniz.
The problems accessible to normal science are all those about mental functioning. How does the brain integrate data from different sources? How do long-term and short-term memory interact? What are the effects of damage here or there in the brain? What are the causes and limits of blindsight or of synaesthesia? Any question framed in terms of human perceptual functioning, or motor or other functions, is in principle accessible to scientific understanding, just as the engineer can relate the functioning of the computer chip to its internal architecture. Here, Leibniz’s demand for an intelligible relationship is satisfied.
By contrast, the hard problem is variously phrased in terms of inner life, the phenomenological feel of things, or the “what it is like” of philosopher Tom Nagel’s famous question, “What is it like to be a bat?” It tries to get a grasp on private experience itself, the river that stops only with dreamless sleep, anaesthesia or death. It says that there is an inner dimension to our lives, which is of fundamental importance. Indeed it makes up our whole awareness of ourselves and our world. But the hard problem is to integrate that inner dimension into the scientific world view.
Philosophers (and lay people) thinking about this tend to divide into two camps. There are those who take the hard problem seriously. And then there are those dismissive, harder-headed theorists who believe the whole idea of a hard problem is a kind of illusion. Once we have done what the computer engineer can do, and have explained everything about human functioning and the mechanisms on which it depends, we have explained everything.
Hard-headed types come in different flavours: reductionists, functionalists or mind-brain identity theorists. Whatever their differences, they join in dismissing the first group as qualia freaks (qualia are the felt or phenomenal properties of conscious events: the painfulness of my pain, felt only by me, for example). Qualia freaks reply that reductionists are insensitive to the difference between a normal person and a zombie, thought of as an unconscious physical duplicate, a thing whose functioning is fine but whose awareness is zero.
Here are some diagnostics for whether you believe in the hard problem. Do you find it completely mysterious that the grey brain can produce the yellow perceptual experience? Do you wonder if a sufficiently large piece of visual cortex alive in a Petri dish might be producing such experience? Do you think that although there are conscious experiences, perhaps they are causally inert, having no effect on bodies and brains? Do you think it a bare possibility, even if unlikely, that you are the only conscious agent on Earth, and that other people are all zombies? If you are tempted to answer yes to most of these questions, you believe in the hard problem.
A generation ago, most scientists would not have done so. They would have thrown in their lot with reductionism of one kind or another. Science deals with what can be observed, measured and repeated. Human reactions, and their neurophysiological bases, can be operationalised. So the line of least resistance is to deny anything further, anything subjective, which cannot. In psychology, this attitude characterised behaviourism, although more sophisticated functionalist views have now overtaken it. Curiously enough, however, recent neuroscience has tended to sympathise with qualia freaks, as the titles or subtitles of these books illustrate. Each writer believes that there is a hard problem, although Christof Koch holds that we can eventually make it disappear by solving enough easy problems. Each hopes that science can at least creep up on it.
A number of developments help to explain this change. One is our increased awareness of the sheer amount of brain activity, and sometimes personal activity, that bypasses consciousness altogether. Many complex sensory-motor reactions are not conscious, and many precede any conscious awareness of the environmental cause that triggered them. So it becomes impossible simply to equate conscious processes with complex functional states of brain and body, for we know of too many such states that have nothing to do with consciousness, and work well enough or better without it. Over most of its activities, a brain is a cluster of small zombies, so we have to postulate something beyond mere function in cases where it is not.
A second development is our increased awareness of possible dissociations between events giving rise to conscious experience, and behaviour expressive of that experience. This makes it attractive to think of the conscious experience as something over and above whatever it does, for it may exist without doing anything much at all. This kind of problem is particularly prominent in Jeffrey Gray’s book, where the dissociation between visual experience and its normal function is highlighted in experiments on synaesthesia.
There are difficulties ahead, however, if you believe in the hard problem. A satisfactory theory of consciousness should protect the idea that consciousness is a good thing. Consciousness makes human life possible. It makes us do things that we might otherwise not have done, and its utility presumably provides the rationale for its evolutionary development. Gerald Edelman is the most forthright of these writers to deny this. He argues that conscious states lie outside the causal order altogether. Physics says that it takes a physical cause to produce a physical effect, and in Edelman’s picture the “phenomenal transform” or conscious discriminations that are themselves the result of underlying neural events can have no effects of their own; in the tradition, this is called epiphenomenalism. It is natural to worry that in that case they are just paint on the machinery, and might as well not exist. But in Edelman’s view they have to exist although they do nothing: they are “entailed” by sufficiently complex underlying neural states. Entailment here means that there is no possibility of the underlying neural states existing without the supervening consciousness: there is no possibility of zombies. There was, as it were, no remaining Lockean act of “God’s good pleasure” to superadd the conscious events on top of the physical events, or to paint the machinery.
In the philosophical literature, there are two models of how to understand such an entailment, or in other words to get rid of the idea of any disturbing Lockean remainder. One, made famous by Saul Kripke and Hilary Putnam (both these philosophers oppose identity materialism), is to assimilate the case to the identity of water and H2O: God or nature had only to make H2O (at the right temperature). It took no further dispensation to make water. The other is the Leibnizian model of rational or intelligible analysis, enabling us to see conscious activity as somehow implicit in the right kind of physical activity. The first of these suggests that there is no hard problem at all: there is only the embodied brain and its physical properties. The second seems equally to require a functionalist dismissal of the hard problem, since it is precisely the hard problem that stands in the way of an intelligible relationship between conscious events and others.
Readers will need to decide for themselves whether Edelman’s approach fits either model, or whether instead, by first cherishing the hard problem, and then helping itself to unexplained entailment, it really suggests only a new name for old-fashioned emergence: magic tissue secreting a magical effect.
A related difficulty is that Edelman is suspiciously silent about another classic problem for qualia freaks: if conscious processes have no causal consequences, it remains very obscure how we could know about them, and still more how we could remember them. Indeed, these problems lie at the heart of Ludwig Wittgenstein’s famous “private language argument” against the cluster of ideas that animate qualia freaks and motivate the hard problem.
Each of these books is stimulating and provoking, and contains a mine of information. The book by Koch, a collaborator of the late Francis Crick, is the heaviest, both in the sense of the largest and the one that goes furthest into neurological and biological detail; his index alone occupies 60 dense pages. Edelman’s Wider Than the Sky, as already hinted, is the most forthright and confident.
But Jeffrey Gray’s Consciousness: Creeping up on the hard problem is remarkable both for the clarity of its expositions, and for the patience with which he explores the prospects for integrating the hard problem into normal science. He does not shrink from counterintuitive conclusions: one of the sections is called “the world is inside the head”, and goes on to defend the philosophically unfashionable view that the consciously perceived world is not the real world.
We should applaud the sensitivity to philosophical issues that each of these writers shows. They illustrate that just as philosophers of mind must know outlines of the latest scientific thinking, so scientists wrestling with these matters do well to cultivate a philosophical sensitivity. As Koch admits, scientists need to listen to the questions philosophers pose, even if they don’t listen to the answers they give. One question we need to prioritise is whether there is a hard question or only a plethora of moderately difficult ones. Here, as scientists like to say, more money is needed for further research.