Abstract
Man can embody truth but he cannot know it.
––W.B. Yeats
This paper is concerned with the nature of the relationship between ‘mental’ mind phenomena and ‘material’ brain phenomena; in other words the ‘mind–brain'or ‘mind–body’ problem. Following an examination of the general nature of the problem, it establishes two working propositions which are employed in the attempt to conceptualize the mind in its relationship to the brain.
A second paper [1] will take these two propositions as a starting point, and explore their logical implications for psychiatry, particularly in relation to theories of causality and aetiology, and the question of how we achieve knowledge of the mind.
Mind and brain
It is an easy matter to define what me mean by the human brain in terms of its general physical characteristics, but a definition of the human mind is more problematic. The Oxford English Dictionary [2] attempts definition in terms of various characteristics or faculties, such as memory, thought, intention, judgement and emotional experience; mind is a ‘mental or psychic faculty’: ‘the seat of awareness, thought, volition, and feeling; cognitive and emotional phenomena and powers as constituting a controlling system, specifically as opposed to matter ’. The final part of this definition reflects the common usageof ‘mind’ as reference to something distinct from matter; the conception that lies at the heart of the ‘mind–body’ problem. Probably no completely satisfactory, and certainly no simple, definition of mind is possible. What will be meant by mind in this paper is consciousness awareness along with the sum of those mental faculties regarded as characteristic of the mind, and in particular the presence of a subjective state of which introspective awareness is possible. In his book The rediscovery of the mind [3] the philosopher John Searle argues that what we recognize as fundamentally characteristic of the human mind is the capacity for consciousness. Searle writes: ‘I will argue that there is no way to study the phenomena of the mind without implicitly or explicitly studying consciousness. The basic reason for this is that we really have no notion of the mental apart from our notion of consciousness’.
While a concept of unconscious mental processes is integral to any sophisticated theory of mind, the questions surrounding the epistemological status of unconscious processes within the mind, and how these might be conceptualized, lie outside of the scope of the paper. The term ‘mind’ will be employed without any implicit assumption about their existence and nature.
Historical background
The mind–body problem has a long philosophical history. A brief note on some of the influential ideas may help place the contemporary situation in perspective. The French philosopher Rene Descartes (1596–1650) is known for his lucid formulation of ‘mind’ or ‘soul’ as something distinct from body, and of which we have indubitable knowledge [4]. Consequently he is often condemned for ‘creating’, the mind–body problem. Gilbert Ryle [5] has suggested Descartes’ formulation contributed to the growth of a myth, which over time has become a kind of official doctrine and dogma in Western society; the dogma of ‘the ghost in the machine’. Although Descartes gave clearer form to the dualist conception of mind as distinct from matter, dualist systems of thought were influential before Descartes and can be traced at least as far back as the ancient Greeks.
Descartes considered mind or soul and body to be ontologically distinct, that is, two things of different essential natures; yet his observation revealed that they seemed to exert effects upon one another. How could two things fundamentally different in nature act upon each other? Descartes postulated that the pineal gland was the seat of mind–body interactions which he conceived of as being mediated by the ‘animal spirits’, but beyond that was unable to specify the mechanism by which such interaction might take place [6].
Contemporary commentators, in highlighting the shortcomings of Descartes’ dualism, often overlook the elegance and clarity of his central formulation in the Meditations: I think therefore I am. Descartes, beginning from a position of epistemological scepticism, apprehended reasons to doubt all commonly accepted forms of knowledge, leaving only the apparently indubitable reality of his own consciousness as a given. There may be grounds to doubt the existence of everything, he reasoned, but the very act of doubting implies at least the existence of one's own mind. This much cannot be doubted: ‘I am, I exist; that is certain’ [4]. Descartes then took this acquaintance with one's own mind as the rational starting point for establishing a system of ontology. In his Sixth Meditation [4] Descartes apprehended that mental events, especially in the realm of understanding or intellect, appeared to constitute an area of discourse distinct from physical bodily events; each area of discourse possessing different explanatory parameters. In Bertrand Russell's words ‘ “I think, therefore I am” makes mind more certain than matter, and my mind (for me) more certain than the minds of others’ and, ‘The decision… to regard thoughts rather than external objects as the prime empirical certainties was very important, and had a profound effect on all subsequent philosophy’. [7]
Since Descartes, formulations and attempted solutions to the mind–body problem have been many and varied, but can be broadly divided into ‘dualist’, which assert the existence of two sorts of ‘stuff’ (substances, processes, being) which coexist, and ‘monist’, which assert the existence of only one fundamental ‘stuff’ which is the basis of all observable phenomena.
Dualist explanations may be further subdivided into interactionist, such as Descartes’, and non-interactionist. The apparently implausible theory of ‘psychophysical parallelism’, as found in the philosophy of Leibniz (1646–1716), provides an example of a non-interactionist dualist theory [8]. Leibniz postulated that there are two kinds of existence, body and mind, which parallel each other but are completely separate and do not interact. Thus their apparent interaction is but an illusion; the consequence of a preordained and ongoing harmony, established originally by God.
A dualist theory of historical importance, and continuing influence within psychiatry, is epiphenomenalism. In philosophical terms an epiphenomenon is a by-product which exerts no causal effect. Epiphenomenalism proposes that mind is a dependent and passive secondary phenomenon caused by the activity of the brain. It is essentially non-interactionist, proposing a one-way causality from brain to mind. Such a view constitutes a rigidly deterministic formulation of mind, and its ascendance was contributed to by Darwin's elucidation of deterministic principles in biology. The concept of soul, so intrinsic to much dualist thought, was threatened, and for many had been routed, by Darwin's evolutionary theory. Epiphenomenalism found particular favour with Darwin's ‘disciple’ Thomas Henry Huxley, who seems to have conceived of man as a kind of biological automaton [9].
Monist solutions fall broadly into three categories: idealist solutions which assert that the ‘stuff’ of the universe is mind and its contents; materialist solutions which assert that the ‘stuff’ of the universe is matter and its properties; and attempts to formulate mind and matter as, in essence, identical, or as different aspects of a unity (this third category could be considered as subsumed under the first two).
The name most closely associated with the idealist option is Bishop Berkeley (1685–1753). Russell [10] summarizes Berkeley's position as a denial of the existence of matter, maintaining that material objects only exist through being perceived. Thus physical bodies are regarded as not existing as such; it is only the ideas of bodies that exist in minds. Elsewhere [11] Russell acknowledges that because no absolute proof of the independent existence of matter seems possible, idealist arguments are difficult to refute decisively. He nevertheless attempts a commonsense refutation of Berkeley's position. He points to the counterintuitive nature of pure idealist theories and their lack of explanatory economy as good reasons not to embrace them. Although idealist perspectives have had great influence within philosophy, they have fared less well in the face of the growth of empiricism in science, and the practical and pragmatic successes that have flowed from the industrial and technological revolutions.
It would probably be fair to say that ‘materialism’ (as a philosophical/intellectual perspective) became the major influence in the West in the twentieth century, with attempted materialist solutions to the mind–body problem asserting the primacy of matter. At the extreme the doctrine of materialism denies the existence of mind. Such an assertion is, probably for most of us, difficult to accept, and might be considered demonstrably false, in that something we call ‘mind’ is apprehended through introspection and seems to require explanation. A less extreme materialism might regard mind as an epiphenomenon, or as something not remarkably different from the brain or body, and therefore reducible to description in terms of physical parameters.
In more recent times, through the perspectives provided by modern physics, matter has begun to look less ‘substantial’ than it once did, and materialist perspectives have developed into physicalist perspectives which look towards the physical universe as a whole, that is, matter and the physical forces and properties associated with matter, in the attempt to conceptualize the mind.
The increase in the influence of materialist/physicalist intellectual perspectives was linked with the rise of empirical methods in the physical sciences, and positivism in philosophy. In psychology, the outcome of the tendency to ignore the mind was methodological behaviourism. The term behaviourism may be applied to a scientific method: ‘methodological behaviourism’, or to a philosophical perspective: ‘logical behaviourism’. The early proponent of behaviourism as an investigative methodology in psychology, B. F. Skinner, in his book Science and human behaviour [12], exhorts his reader to forget about mental phenomena, which seem to be regarded as irrelevant. He writes that in certain situations ‘the mind and the ideas, together with their special characteristics, are being invented on the spot to provide spurious explanations. A science of behaviour can hope to gain very little from so cavalier a practice. Since mental or psychic events are asserted to lack the dimensions of physical science, we have an additional reason for rejecting them’.
In The concept of mind [5] the influential philosopher Gilbert Ryle attempted to undermine the supposed dogma of the ‘ghost in the machine’, by arguing a form of ‘logical behaviourism’. Ryle suggests ‘… the styles and procedures of people's activities are the way their minds work and are not merely imperfect reflections of the postulated secret processes which were supposed to be the workings of minds’. Ryle also attempts to invalidate Descartes’ concept of privileged access to one's own mind by arguing that self-knowledge and knowledge about others are on a parity: ‘The sorts of things that I can find out about myself are the same as the sorts of things that I can find out about other people, and the methods of finding them out are much the same’. While there is much commonsense here and, as Ryle argues, it seems probable that we obtain our understanding of the way others’ minds work from their behaviour, it is hard to see how Ryle's arguments can do justice to the reality and dimensions of subjective mental experience. An observer's understanding of a person's behaviour can never constitute a full knowledge of that person's mind; there always remains an inaccessible and ‘ghostly’ aspect in the experience of another. In order to fully know the nature of another's experience of physical pain, I would have to feel his or her pain; presumably not a possibility (see below) (see also Wallace [13] for a critique of some aspects of Ryle's logic from within a psychiatric framework).
With the development of increasingly sophisticated techniques for direct brain investigation in the second half of the twentieth century, the main focus for scientific investigation of mental states has shifted from the empirical observation of human behaviour, to the empirical observation of the brain. Research over the course of the last century has provided increasing evidence for the linkage between mental events and physical brain events. Contemporary monist materialist views propose an identity between mental states and states of the material brain.
Today most of us would probably accept the proposition that the existence of the mind is in some way contingent upon the existence and function of the material brain. We would regard the function of the mind as intimately and probably inextricably linked with the function of the brain, and we would not expect a mind in the absence of a functioning brain.
The contemporary situation
If mental events are contingent upon brain events in this kind of way, does that mean they are reducible to brain events? Many scientists and philosophers hold such a view, and within psychiatry it seems a commonplace assumption. There can be no doubt as to the influence of reductionist materialist/physicalist perspectives, and the dominant view in the West in the latter half of the twentieth century would seem to be a materialist ‘identity theory’ which posits that mental events are in fact brain events, and may be fully explained as brain events, thus the title of Daniel Dennett's book championing this position: Consciousness explained [14].
There have, however, always been voices arguing the impossibility of a reductionist materialist understanding of mind. In 1960 the biologist Seymour Kety wrote in Science [15]: There remains one biological phenomenon, more central to psychiatry than to other fields, for which there is no valid physiochemical model and (or so it seems to me) little likelihood of developing one; this is the phenomenon of consciousness – the complex of present sensations and the memory of past experience which we call mind.
He goes on to suggest that, ‘one can acknowledge the existence of consciousness and of matter and energy without insisting that one must be reduced to the other’.
Similarly the philosopher John Searle, in his recent book, The rediscovery of the mind [3] identifies the tendency in materialist doctrines ‘to deny the existence of any irreducible mental phenomena in the world’. Searle asks, ‘Now why are they [the reductionists] so anxious to deny the existence of irreducible intrinsic mental phenomena? Why don't they just concede that these properties are ordinary higher-level biological properties of neurophysiological systems such as human brains?’ Searle argues the need to accept the ‘obvious facts about our own experiences – for example, that we are all conscious and that our conscious states have quite specific irreducible phenomenological properties’, is as necessary as the need to accept the ‘obvious facts of physics’.
Searle goes on to argue that the mistake is to view the irreducibility of mental phenomena and the contingency of mind upon brain as incompatible realities which therefore imply a form of dualism. Searle asserts the irreducibility of mental events to physical events, but rejects dualism.
David Chalmers is another contemporary philosopher unimpressed by attempts to formulate a reductive materialist solution, but he is also unimpressed by Searle's idea that the phenomenon of consciousness is an instance of an ordinary higher level biological property, essentially similar to other higher level biological properties. Chalmers [16] points out that the phenomena of consciousness differ from all other phenomena in that: ‘Our grounds for belief in consciousness derive solely from our own experience of it’. Chalmers argues that consciousness is not logically entailed by the physical facts of the functioning human brain; that is consciousness is not ‘logically supervenient’ upon these facts: From all the low-level facts about physical configurations and causation, we can in principle derive all sorts of high-level facts about macroscopic systems, their organization, and the causation among them. One could determine all the facts about biological function, and about human behaviour and the brain mechanisms by which it is caused. But nothing in this vast causal story would lead one who had not experienced it directly to believe that there should be any consciousness.
Chalmers’ argument here seems analogous to the argument entailed in the ‘problem of other minds’; that is the problem of how we can ever know that someone else has a mind. An observer may infer from a person's behaviour and what he says about himself that the person is conscious, but it is not something of which the observer can have certain knowledge, nor confirmation by direct experience of the phenomena of that consciousness; it is an inductive inference rather than a logical necessity. Similarly, an observer may monitor the activity of a brain, and infer that the brain possessed consciousness, but can have no direct knowledge of this consciousness. The observations about a brain which form the basis for inference do not logically entail the existence of consciousness. Acquaintance with the existence of consciousness comes through one's own experience.
Many scientists and some philosophers, such as Dennett [14], have asserted either that the mind–brain problem has disappeared, or will eventually disappear, in the face of the growth of scientific knowledge about the functioning of the brain; that the burgeoning knowledge, consequent upon advances in investigative neuroscience, has finally proved that the human mind and brain are indeed one and the same thing.
Despite the evidence for the existence of a close correlation or ‘identity’ between brain events and mental events, and despite the fact that this evidence has shaped the way the mind–brain ‘relationship’ is conceptualized, there remains no consensus as to the correct understanding of the nature of this ‘relationship’. It is, I think, probably mistaken to believe that growth in scientific knowledge can lead to such an understanding. That is to say that the essence of the problem remains a matter of metaphysics rather than physics.
The problem
The assumption that the mind–brain problem will eventually be solved by science arises from a failure to recognize the nature of the problem. We already have sufficient grounds to assume, as a best hypothesis, that mental events and brain events constitute a fundamental unity; that there is at least an ‘identity’ of correlation between specific brain events or states and specific mental events or states. Ever since evidence for the link between mental and brain events has been available, some kind of identity theory has seemed the most reasonable working hypothesis. The details of a sophisticated contemporary scanning study linking mental activity and brain physiology reveal nothing essentially different, in relation to the mind–brain question, from say, Wilder Penfield's classic studies of cortical stimulation carried out more than 50 years ago [17]. Both studies provide data of the same explanatory order. Further scientific research is likely to reveal increasingly fine-grain data about the mind–brain relationship, but it cannot be expected to yield data of a new explanatory order. Substantial evidence already exists for the mind–brain correlation that would be predicted by some form of ‘identity’ theory, and it seems a reasonable assumption that further research will provide consistent data.
The problem that science probably cannot reach is how to give a satisfactory explanation of mental experience, or the phenomenology of consciousness, in terms of the brain. There does not seem to be a way. Any attempt at explanation inevitably ends up leaving out the mind.
The difficulty may be stated something like this: even if it were possible with sufficiently sophisticated scientific instruments to observe and measure all the neurophysiological correlates of a specific mental event, for example feeling a pain in the finger, this cannot communicate the essential subjective experience of the pain to the observer. An independent observer of these brain processes does not have a painful experience in his finger; he sees the various manifestations of neurophysiological processes. Even if he is aware that these manifestations equate with ‘feeling a pain in the finger’, he has no direct access to the subjective experience of the experimental subject, only indirect access, by inference, or from the subject's communications, about the experience. Any empathic identification with the pain experience on the observer's part remains just that, not the thing in itself. There is, it would appear, no way to get the essence of a subjective mental experience by observing a brain; this essence remains personal, and ‘ghostly’.
An hypothetical example (slightly modified) taken from Chalmers’ book The conscious mind [16] (adapted from Jackson [18]), may help to illustrate this. Imagine we live in an age of completed neuroscience, and know everything there is to know about physical processes in our brains. Mary has been brought up wearing spectacles which screen out colour, so she can see only black, white and grey. She has never taken them off and has never seen any colour. Mary is nevertheless very well educated as a neuroscientist specializing in the neurophysiology of colour vision. ‘She knows everything there is to know about the neural processes involved in visual information processing, about the physics of optical processes, and about the physical makeup of objects in the environment’ but she has never seen any colour. No amount of reasoning from the physical facts that are known to her can lead her to know what the experience of seeing in colour is like, for example ‘she does not know what it is like to see red’. ‘It follows that the facts about the subjective experience of colour vision are not entailed by the physical facts. If they were, Mary could in principle come to know what it is like to see red on the basis of her knowledge of the physical facts. But she cannot.’
In Chalmers’ terminology, the mind and experienceare ‘naturally supervenient’, but not ‘logically supervenient’ upon brain activity. Natural supervenience reflects the contingency of mind upon brain; that in all probability the mind cannot exist without the brain. Nevertheless experience or mind is not logically supervenient, in that a full knowledge of brain events cannot lead to a full knowledge of the subjective experience of the mind that accompanies the brain. Or again, Chalmers comments, ‘Whether or not consciousness is a biochemical structure, that is not what “consciousness” means ’.
In Levine's terminology there is always an ‘explanatory gap’ between physical explanations of brain processes and the nature of experience in the mind [19]. The subjective quality or ‘feel’ of experiences, referred to by philosophers as ‘qualia’, has a non-reductive aspect. Another way of putting this is that even if we assume our conscious mind is our experience of the activity of our brain, and even if we adopt a theory of the unity or identity of mind and brain, we do not and cannot, experience mind and body/brain as identical.
Thus the problem that confronts us can be stated in terms of two propositions (constituting a ‘double aspect theory’) as follows:
1. The faculty of mind is contingent upon the functioning human brain; in this sense mind and brain constitute two aspects of a unity. At a fundamental level there appears to be an ‘identity’ between specific mental states and specific brain states upon which they are contingent.
2. Any attempt to explain the subjective essence of a mental state or process in terms of a brain state or process must inevitably fail as it leaves out the ‘mind’ that we seek to explain. Discourse about mental states is not reducible to discourse about brain states, and therefore brain states and mind states are not identical. (If x is identical to y then any property of x is also a property of y, and vice versa. Subjective mental events and objective brain events have distinct and differing properties.)
Both these statements can, I believe, be reasonably judged to be true: the first on the basis that it best fits the available scientific data; the second on the basis that it is a self-evident truth. However taken together they are difficult to reconcile; they result at best in a paradox, at worst in logical incompatibility. On the one handwe ‘know’ that mind and brain in some fundamental way constitute unity, or exist in an ‘identity’; on the other hand our experience of our own mind cannot be reduced to description of brain processes and nor can the essence of mental experience be constructed out of knowledge of brain processes. How these non-identical constructs can be an ‘identity’ remains mysterious.
Whatever the logical difficulty in reconciling these two statements, it is no greater than the logical difficulty presented by other formulations, or ‘solutions’ to, the mind-brain problem. As Wallace [13] comments, ‘At the current level of psychological, biological, and philosophical sophistication any approach to the mind–body problem is scandalous; none avoids logical and empirical pitfalls’. The question continues to preoccupy philosophers precisely because no satisfactory solution has been formulated. All attempted solutions to-date suffera ‘fatal’ flaw of incompleteness or internal contradiction, and the proposed formulation fares no worse in this regard. Any greater plausibility of the proposed formulation over alternatives rests solely on whether one judges the ‘commonsense’ validity of the propositions to be sufficiently compelling.
If the arguments put forward here are accepted, then we are left with a mystery at the heart of the mind–brain relationship; we simply cannot imaginatively grasp how mind comes about as a consequence of certain arrangements and activities of matter, but we know that it does. Furthermore, it seems unlikely that further scientific research, upon either brain or mind, can help us. If we take Searle's position then, despite the conceptual difficulties, we know the answer to our problem is that mind is a property of brain, and in principle this need be no more mysterious than the fact that liquidity is a property of water under certain conditions [3]. Chalmers, in contrast, believes that the situation is much more mysterious indeed, and argues persuasively that consciousness is a property that stands in an altogether different relationship to the brain than liquidity does to water [16].
Even if we wish to avoid a dualist view we seem to be stuck phenomenologically with a sense of duality; we simply experience mind and body as distinct. There is a mystery at the heart of the mind–brain ‘relationship’ which it seems impossible for the mind to grasp, just as it appears to be beyond the capacity of the human mind, at least in its current state of development, to imaginatively grasp the concept of infinity. Regarding the problem as amenable to solution by the means of science appears to have more to do with wish than reality.
Commentators in psychiatry often contend thatthe ‘Cartesian’ distinction or ‘split’ between mind and body/ brain is an artificial dichotomy and an imposition upon the unity that constitutes reality, and exhort us to transcend this artificial distinction in our thinking. While it may be necessary to strive to transcend this dichotomy whenever it threatens to limit clinical thinking, it does not follow that ‘dualist’ thinking is problematic in principle, and therefore something to be dispensed with. In any case this is hardly possible. As has been argued, in order to think about the mind and its activity we need to have a concept of mind, and this inevitably involves distinguishing mind from either body or brain.
Our experience of duality would seem to be an unavoidable consequence of the emergence of a self-aware and self-reflecting mind. I suggest that one cannot have a mind, at least not a ‘modern’ mind without it, and that if we wished to do away with this sense of duality we would have to be willing to forego the capacity for thoughtful self-awareness that constitutes our mind. For all the criticism that has been levelled at Descartes, he was, in his willingness to take the mind seriously, essentially a modern thinker.
By this view the human ‘mind’, in a collective historical sense, is also a developing function, and probably has different capacities today than it did, say, before Descartes’ time. This being so, the possibility cannot be excluded that, in its collective function, the human mind could yet evolve to the point of possessing the capacity to imaginatively grasp how it emerges from matter.
Footnotes
Acknowledgements
I am grateful to the Melbourne philosopher Tamas Pataki for his helpful critique of this paper.