I shall introduce my problem with the help of that well tried Philosopher's device, the imaginary world. Let us suppose that we have two parallel coexisting universes. Universe A is our actual familiar universe and so, for the moment, we need say no more about it. Universe A' is an exact physical replica of A such that for every physical object that exists in A there is a corresponding object in A' and for every physical event that occurs in A there is a corresponding physical event in A'. The one and only feature which serves to distinguish between A and A', apart from their spatial separation, is the fact that in A' there are no mental entities Or conscious experiences. Thus, although the whole of evolution and the whole of history unfolds in A' exactly as it does in A, so as to be indistinguishable to an observer, there are no observers in A', no one indeed who is aware of anything that happens there, if to be aware is to have a conscious experience.
I am here assuming that being conscious entails having a mind although having a mind does not necessarily imply being conscious, there is, I would say, nothing self-contradictory in the idea of unconscious mental events. However, consciousness is, by common consent, the most distinctive attribute of mind and it would be hard to make sense of a mind that never at any time became conscious. At all events Universe A' is, ex hypothesi, a purely physical or totally mindless universe.
Given this hypothetical situation we can now state our problem as follows:
Why should our actual world correspond with Universe A rather than with Universe A'? If this is a valid question it admits of only two answers. Either there is no reason at all, it is just a God-given or contingent fact that that is how things actually are, like the fact that anything at 11 should exist rather than nothing, or else there is some reason, for example we might suppose that the world we know could not have evolved as it has done had it not been for the intervention of mind.
The first answer, that from an a priori standpoint A and A' are equally probable candidates for actualisation, presupposes that mind plays no part in the determination of physical events. The second answer which asserts that A' is no more than a logical possibility and could never be actualised implies that mind has some degree of autonomy in determining the course of events. Materialism is a name that has been given to a variety of a doctrines but, as I shall use the word here, a materialist is one who is logically committed to giving the first answer. Similarly, what I shall call Interactionism will here be taken to mean the doctrine which logically commits one to giving the second answer. The purpose of the present paper is to examine these two doctrines and assess their relative merits. I shall try to show that there are no insuperable or logical objections to either of them, whatever may have been said to the contrary, and that there are manifold advantages and disadvantages whichever one we adopt. Accordingly in present circumstances it must remain a matter of one's personal philosophical predilections which of them one chooses (my own happens to be for the second but I shall try not to let that influence the argument). However, with the growth of knowledge, circumstances may change and I will end by discussing what would need to be the case before it became more rational to prefer one or other given alternative.
Before I can even embark on this plan, however, we must first consider very carefully whether the hypothetical situation we took as our point of departure is indeed a legitimate one and is not perchance vitiated by some internal inconsistency or conceptual incoherence as many might protest. It is after all only too easy to think up situations which, on examination, turn out to be logical absurdities. We have only to think of that favourite device of the science-fiction writer, time-travel. This seems innocuous enough when it is first introduced into the narrative but very soon we are beset by all kinds of insoluble paradoxes. Could it be that our imaginary world, Universe A', was in fact just such another flawed fantasy ?
Like time-travel, one must admit that it has some very bizarre consequences. Consider the following thought-experiment.
We take an individual P, let him be a family man, from Universe A and suddenly and instantaneously we exchange him with his counterpart P' from Universe A'.
The first thing we may note about this thought-experiment is that it produces absolutely no observable differences to indicate that anything whatever has changed. P's wife and children will never know P' is not the husband or father whom they knew and cherished, that indeed he is not a person at all but an insentient automaton. For, ex hypothesi, nothing in the appearance or behaviour of P', no far-away look in his eyes or anything of that sort can ever betrays the secret to which we are privy. Likewise, if we follow the adventures of P flow transposed to A', we know that he can never discover his solipistic predicament, he will continue to believe that the beings which he takes to be his wife and children have minds like his own. But while this is certainly bizarre, it generates no paradox of a logically objectionable kind. It is absurd only because A' is an absurd universe, our thought-experiment has done no more than make explicit the well known truism that no object however life-like and no behaviour however mind- like can ever entail the presence of consciousness. It is true that, on any positivist criterion of meaning, our thought-experiment must be dismissed as meaningless since it is in principle impossible to verify that it has been carried out. And yet, provided we can understand the distinction between A and A', P and P', the supposition that such an exchange has been made is perfectly intelligible. Indeed the intelligibility of such a thought-experiment could well be advanced as a conclusive refutation of the positivist theory of meaning.
In view of what has just been said it is surprising to find how large a slice of the recent literature on the philosophy of mind would, in defiance of the truism which we have just enunciated, disallow the distinction we have made. I suppose the two most important doctrines in this connection are (1) Logical Behaviourism (Ryle 1949) and (2) Central State Materialism (Armstrong 1968). If, therefore, we can deal with the objections from these sources we may feel reasonably confident that we stand on firm ground.
Now, according to the former, what it means for an organism to be conscious or sentient is nothing over and above its being disposed to react to situations in an appropriate or discriminating way. The elimination of any existential element from consciousness by means of this stipulative redefinition of the concept derives such plausibility as it may possess from the ambiguity of the word consciousness as used in everyday discourse when it is seldom necessary to distinguish between the behavioural criteria for the ascription of consciousness and consciousness as such. Thus, when the doctor is called in to pronounce whether the victim of the accident is conscious or not we are normally quite content to accept his verdict as final. And yet, logically, it is perfectly permissible to surmise that even when the most refined physiological tests known to medicine show that the patient is comatose, that is behaviourally unconscious, he may nevertheless be experiencing some vivid hallucination or out-of-body experience and hence conscious in the basic sense. It is, of course, exclusively in the basic sense, not in the derived behavioural sense, that the inhabitants of our Universe A' are said to be unconscious.
We should note, at this point, that it is only in its derived sense that we can define or explicate what we mean by consciousness. In its basic sense it can no more be defined than any other primitive concept. With any primitive concept, either one understands what is intended or one fails to understand. A logical behaviourist may be defined as someone who has failed to grasp what consciousness means in this sense. Confronted with a logical behaviourist various strategies may be adopted in order to get him to understand what we mean. A nice example is that suggested by Kirk (1974) who asks us to imagine ourselves converted step by step into a "Zombie" (his name for our counterpart in A') by losing one sense-modality after another while continuing to behave in a normal fashion. However, if all such strategies fail and our logical behaviourist persists in denying that he understands what we are talking about, the dialogue can go no further; all that we can then do is to echo Dr Johnson when he declared that while he could give his opponent an argument he could not give him an understanding.
But, if we reject Logical Behaviourism, then, by the same token we must also reject Central State Materialism which equally refuses to recognise the primary connotation of consciousness. Indeed, the latter doctrine differs from the former only in that it literally identifies the mental states and processes with the relevant brain states and processes. Mentalistic talk, we are told, is essentially 'topic-neutral', by itself it tells us nothing about its ontological reference, however science gives us the authority to go beyond this neutrality and construe it as referring to the activities of the brain. But if that were so there would be absolutely nothing that we could say about the inhabitants of A that we could not equally say about the inhabitants of A' since, ex hypothesi, they have identical brains. As it is, however, we have said that the former have conscious experiences while the latter do not. For those to whom this statement is intelligible both of these proffered solutions of the mind-body problem are non-starters.
The two viable forms which materialism may take are, first, the old-fashioned epiphenomenalism which regards the mind-brain relationship as a causal relationship but one in which the causation works in one direction only so that mental events figure only as effects, never as causes, and, secondly, the more recent double-aspect or double-attribute theory, as it is variously known, according to which the mind-brain relationship is one of actual identity, that is to say mental events are conceived of as brain events but as such events are apprehended by the brain itself as opposed to the way in which they are apprehended by an external observer (i.e. by another brain). This latter theory differs from the Central State version of the identity theory in that it treats consciousness as an irreducible fact, not as something needing to be analysed in dispositional terms. Various conceptual advantages have been claimed for it over the earlier epiphenomenalist theory but whether, in the last resort, anything more is involved than a mere verbal shift or, indeed, whether it even makes sense to talk about an identity in this context is still very much open to question. These are not questions, however, which we need pursue here for, whether we say that the mind is a function of the brain or whether we say that it is the brain in one of its aspects, the explanatory weight rests wholly upon the physical processes involved. Hence both forms of materialism carry the same implication, namely that even if, per impossibile, the brain did not generate conscious experiences or even if it had no other aspect than the physical one, even so everything else would go on exactly as before.
Despite repeated attempts by philosophers to discover some knock-down argument which would show, once for all, that materialism or interactionism, as the case may be, was an untenable position, the persistence of both suggests that such attempts have been less than successful. The problem to which we must now address ourselves is which position has the greater claim on our allegiance, all things considered?
The immediate difficulty is that, traditionally, materialism takes its stand on, and draws its strength from, science whereas, traditionally, interactionism appeals to our common sense or moral intuitions. It is true that interactionism as a doctrine was first formulated by Descartes who was also one of the chief architects of the scientific revolution but he may have been swayed by his religious commitments, certainly his doctrine held little attraction for his successors. At all events, by the late 19th Century, at a time when science had reached a peak of self-assurance and was pressing its right to be considered the final arbiter on the nature of man, epiphenomenalism had become the orthodox scientific position on the mind-body issue and, in effect, it has remained so ever since.
Meanwhile those philosophers who could not embrace materialism gravitated for the most part to one or other form of Idealism. From this lofty vantage point science itself could be viewed, not as the one objective authority which alone can legitimate our beliefs, but as just one of the creative manifestations of the human intellect and imagination which, however great its practical importance, could not take precedence over other equally valid belief-systems. In our own day, when Idealism ceased to be fashionable, philosophers have argued in a similar vein that science is no more than a specialised activity which cannot, in the nature of the case, overturn the view of mind sanctioned by ordinary language. Interactionism was kept alive in the meantime by those few who took scientific materialism seriously enough to try and refute it on its own grounds. They numbered among their ranks philosophers, psychologists, physiologists and, of course, psychical researchers, but, despite the eminence of some of the names one could cite, theirs was a minority position which continued to bear a somewhat heretical or, at least, deviant taint.
In what sense can it be said that science lends support to materialism? The answer, I suggest, is twofold.
First, in the theory of evolution, materialism finds at least a plausible cosmology; secondly, the science of neurophysiology presents us with some striking demonstrations of the one-sided dependence of mind on brain.
From our point of view what was important in Darwinism was not so much that it explained the origin of species with recourse to supernatural intervention but that the one simple principle of the survival of the fittest - perhaps the most fertile principle in the whole history of ideas - could be applied quite generally to explain any semblance of design or purpose in nature wherever there is random variation and natural selection. Thus evolution is by no means restricted to phylogenesis. We talk of the evolution of galaxies out of the primeval inter-stellar dust or the evolution of organic and macro-molecules out of the elements just as appositely as we talk of the evolution of intelligent life from simpler organisms. In the face of this smooth cosmological sequence it is not easy for the interactionist to gain a foothold. For, if inanimate nature evolved of its own accord as a result of exclusively physio-chemical processes; if, furthermore, the whole of the plant kingdom in all its prodigious diversity evolved without the benefit of mind, as presumably did much of the animal kingdom as well in its lower echelons, is it plausible to suppose, as the interactionist must, that somewhere there is some definite point beyond which further development would not have been possible had not mind providentially supervened? Nor is it only in the phylogenetic sequence that continuity must be breached in this unlikely way for the same question arises with respect to the ontogenetic sequence of individual growth and development.
Does mind cohere with matter at conception? At birth? At some point intermediate between these two events? And, if the latter, is the union automatic and invariable? Or, if not, does a mindless embryo fail to develop and so perish?
One has only to pose such questions to realise how difficult it is to reconcile an interactionist metaphysic with modern biological knowledge or to appreciate why a latter day Darwinian, like Monod (1971), should champion materialism. Moreover there exists no credible cosmology that would account for the origins of mind or provide a reason for the intrusion of mind into a mindless universe in the first instance, at best we have the various mythical, religious or occult systems of a prescientific vintage to fall back upon. In desperation some anti-materialists have opted for a pan-psychism according to which mind
inheres in all matter everywhere even though its presence is somehow made more manifest in the brain. However, while this restores a measure of continuity, it is an extravagant solution with its implication that we are potentially conscious in every atom of our body!
The argument from brain-science has perhaps an even more direct bearing on our problem than the cosmological argument we have just considered. The critical evidence in this connection comes from the study of brain damage, whether due to injury, disease or deliberate surgical intervention. The point here is that, if the interactionist is right to attribute some degree of autonomy to mind, we would expect that we would be able to circumvent to some extent such localised disruption, perhaps by using other parts of the brain, whereas the evidence suggests, on the contrary, that, in the adult brain at least, quite small lesions may suffice to cause the loss of vital cognitive and motor functions or even, in some cases, drastic deterioration in the personality of the afflicted individual. Even when, by an heroic effort, the individual learns to adopt strategies to compensate for his disabilities, as with Luria's patient, the deficit remains (Luria 1972). Sadly we must admit that, in this context, the triumph of mind over matter is, at best, no more than a figure of speech.
One special type of brain damage that has already provoked a certain amount of philosophical controversy is that resulting from the so-called split-brain operation, or commissurotomy, an operation that is carried out only in certain very severe cases of epilepsy as a means of restricting its scope. A patient whose corpus callosum has been severed is without the normal physical means whereby information received at one cerebral hemisphere is transferred to the other. Although such a person is able to function more or less normally in daily life - so much so, indeed, that it was many years before it was realised that the operation had these consequences - when tested in special situations that can be contrived in the laboratory it could be shown that the two hemispheres were functioning autonomously and even, in certain circumstances, at cross-purposes with one another!
Such a demonstration was possible because, with the cutting of the optic chasm visual stimuli from one half of the visual field would go only to the contralateral hemisphere while tactile stimuli from one side of the body would go only to the ipsilateral hemisphere. As a result of the pioneer investigations of Sperry in the 1960s and of the work of his successors we now know that a set task can be successfully accomplished under the control of one hemisphere alone without the other hemisphere evincing any sign of knowing what has happened. Since it is the left hemisphere that contains the speech centres this means, in particular, that the split-brain subject will deny any knowledge of an object that has been presented exclusively to his right hemisphere even when, by the appropriate response of his right hand, he has just indicated his recognition of it! (Sperry 1965; Trevarthen 1974).
The philosophical problem which arises out of these facts is how we should best describe such a paradoxical situation ? Are we to say that the subject's mind, like his brain, has now been split in two yielding two parallel streams of consciousness insulated from one another ? Or should we say, for example, that the subject's mind is now associated exclusively with his dominant left hemisphere leaving the mute right hemisphere to function purely automatically and unconsciously ? Nagel (1971) has drawn attention to paradoxical consequences of any attempt to interpret the situation in terms of our familiar concept of the self. Zangwill (1976), on the other hand, has voiced a strong plea for adopting our first suggestion and acknowledging frankly the duplication of consciousness. At the same time he rebukes Eccles for adopting our second suggestion stigmatising it as a desperate rear guard bid to preserve the integrity of the soul. As Zanguill very aptly points out, by all the criteria we normally apply when ascribing consciousness, with the exception of speech, the activities associated with the right hemisphere in the split-brain cases merit the attribution of consciousness and to withhold it must incur the suspicion of special pleading. Moreover he mentions at least one instance where the patient's entire left hemisphere was removed and yet this patient did not thereafter appear to be any the less of a conscious human being.
From the standpoint of the interactionist these discoveries are undeniably disconcerting precisely because they bring out so dramatically the dependence of mind on brain. Indeed long before commissurotomy was a practical possibility its hypothetical implications were being discussed by thinkers of rival persuasions (Zangwill 1974).
The dominant view, represented by Fashioner who believed in mind and matter as parallel realities, was that the mind like the brain would become divided and in course of time two distinct personalities would emerge depending on which hemisphere was engaged. The minority view, represented by McDougall who was a staunch interactionist, insisted that the unity of consciousness and of the self would be preserved and that its preservation might afford the most convincing proof for the existence of the soul! What, then are we to say now that we know what transpires? We cannot say that either party has been completely vindicated. Except under the highly artificial conditions of the laboratory the personality of the split-brain patient survives intact. What happens, it seems, is that the dominant or conversant left-hemisphere takes charge and represents the individual to the outside world. At the same time the subject's behaviour in the experimental situation is hard to reconcile with a McDougall Ian or Cartesian unity of consciousness. However, this unity had already been severely undermined by the increasing evidence that came to light during the late 19th Century of dissociated states and automatisms. Such bizarre phenomena as automatic writing, secondary, alternating and even co-conscious personalities, fugue states, amnesic episodes and suchlike - all of which were well known to McDougall who had to do his best to grapple with them (Boden 1972 Chap 7) - raised questions about the unity of mind no different in principle from those presented by Sperry's evidence.
When the concept of the unconscious was still a novelty there was a division of opinion which anticipates that between Zangwill and Eccles about what was involved in unconscious activity. Some, like Zangwill, wanted to postulate a secondary centre of consciousness to go with it which remained inaccessible to the subject's primary consciousness. Others, à la Eccles, wished to deny it the title of mental activity and regard it as the routine workings of the cerebral machinery, no different in principle from the autonomic and reflex activity of the nervous system that likewise takes place outside our conscious awareness or control. The long Empiricist tradition in philosophy which equated mind and consciousness made it seem inevitable that, when confronted with clear evidence of intelligent or adaptive behaviour that was not accessible to introspection, either one had to posit an extra centre of awareness or else regard such behaviour as the activity of a sophisticated natural computer. A third possibility, namely that mind might manifest itself unconsciously, although a commonplace among psychical researchers, was rarely entertained.
Even the depth psychologists who followed Freud, who were so preoccupied with the unconscious, were, for the most part, content to adopt a non-committal attitude regarding its ontological status provided they were allowed complete freedom to develop their theories independently of current physiological knowledge. We, however, who have liberated ours elves from the positivist dogmas of Empiricism, should have no trouble acknowledging that our unconscious actions may be no less under the control of mind than our conscious behaviour.
Consciousness may well be the most distinctive sign of mentality but there is no reason why we should regard them as synonymous. In the case of the severed right hemisphere discussed by Zangwill I have no doubt that its ativities were controlled by some sort of a mind but, whether that mind is conscious or not and what relationship it hag to the mind which governs the subject's dominant left hemisphere are questions about which I must profess myself agnostic I will merely point out, before we leave the topic, that it would be unwise to make so much of these rare anomalous cases, however intriguing or important they may be, as to overlook the truly astonishing degree of unity and coherence which obtains in our normal waking consciousness. To quote Eccles: "Our brain is a democracy of ten thousand million nerve cells, yet it provides us with a unified experience". (Eccles 1965 p.36).
We have now covered at least some of the ground where materialism could be expected to make most of the running. It is time to turn to a different realm where the roles are reversed and it is materialism that is on the defensive.
No philosopher, however partial to materialism, would deny that the way in which we think about one another's behaviour in real or the way in which this is reflected in all our ordinary discourse, is, in its presuppositions and in its implications, overwhelmingly interactionist. For example, in real life it is universally assumed that the fact that we consciously choose to do something is causally relevant to the fact that we do it. To the materialist, on the contrary, both our conscious choice and the subsequent movement of our limbs are alike the effects of the particular brain state we happen to be in at the time or, more specifically, perhaps, of the particular distribution of electric charges in the cortex which determine which nerve cells will fire and in what order. No amount of philosophical double-talk (and there has been plenty) can disguise the fact that we have here a massive contradiction which cries out for a resolution one way or the other.
The demand is even more insistent in the case of our moral discourse. The language of praise and blame, of pride and remorse, are meaningful only if the ultimate responsibility for the action resides in the agent. If a computer makes an error we do not hold it morally responsible for deceiving us, yet it is hard to see why, if we are indeed just conscious automata, as the materialist supposes, we should be held morally responsible for anything that we do.
Even those philosophers, the so-called 'soft determinists' who maintain that, in principle, there is no incompatibility between physical determinism and the existence of free-will, now usually concede that, in practice, we cannot at one and the same time conceive of ourselves as physical objects and as moral agents. There is, it seems, a fundamental antagonism between these two conceptions, to pass from one to the other demands a gestalt switch of a kind that can be achieved only with exceptional mental agility.
The materialist can, of course, dismiss free-will as an illusion and moral judgments as nonsense, as do the 'hard determinists', but, while many philosophers from Spinoza onwards have adopted this course none, I think, has successfully transferred it from the study to the market-place for the simple reason that, in practice, it is virtually impossible to abstain from moral judgment. Hence the hard determinist lays himself. open to the charge of bad faith. None of this, of course, disproves materialism or determinism because our moral intuitions may just be confused but it does expose the strong counter-intuitive element in these doctrines.
What, in the end, makes materialism irretrievably implausible (though not necessarily false!) is precisely that which makes our imaginary universe A' so unbelievable. If the interactionist is right in supposing that the presence of mind is necessary in order to produce mind-like behaviour, then it is perfectly understandable why there should never be a state of affairs like that represented by our universe A'. But, if, on the other hand, the materialist is right and there is no reason at all why we ourselves should be conscious rather than non-conscious, then there is nothing even improbable about the situation that obtains in A'. Indeed, if we one day encounter intelligent life elsewhere in the universe, where evolution may be presumed to have taken a different course, we would have no grounds whatever for assuming that these alien beings were sentient creatures like ourselves. Worse still, the materialist is peculiarly vulnerable to solipsistic doubts even when among his own kind.
The fluke which made our species conscious might, perhaps, have occurred only in his own unique case, he might be a complete sport in that respect. He cannot invoke the traditional analogical argument for rejecting solipsism, namely that behavioural similarities between ourselves and others justify the ascription of consciousness to them no less than to ourselves. For, by his own admission, mind plays no part in the determination of behaviour. The ultimate paradox of materialism is that the one feature of the universe which alone gives meaning to all the rest is the one feature which has to be declared redundant! Nothing can account for its emergence; nothing follows from its existence.
Such considerations, however, are too abstract and metaphysical to count for much with the materialist. For the truth is that the strength of materialism has never been its logical cogency but rather its pragmatic or heuristic value for science. By this I mean that if we adopt a materialist approach to the phenomena of life or mind we open up the prospect of a reductive explanation and even if this is never attained at any rate we have not upset the unity of the sciences; nowhere are we forced to introduce some new entity or principle that has no equivalent elsewhere in science. Now, contrary to what some philosophers have written, reductive explanations are by no means the only valid type of explanations but they are, undoubtedly, the most powerful, perhaps for the same reason that physics is the most powerful and universal of the sciences.
It is true that when we come to the behavioural sciences there is precious little that admits of a reductive explanation but even if what we have is no more than an abstract theoretical model it provides a challenge to the neurophysiologist to explain how it might be embodied in the brain, thereby completing the conceptual bridge linking behaviour at one end to physics at the other.
It is now generally recognised that explanation in psychology is a two-stage affair. This is best illustrated, I think, in the cognitive sphere.
We start by asking how is it possible for us to acquire skills or solve problems; how, for example, do we contrive to recognise a melody? Ride a bicycle? Put our thoughts into words etc.? At this stage someone comes along with a theory. No reference is yet involved to the brain but if the theory is at all rigorous it should be possible to program a computer to simulate the activity in question. At this stage, which we might call the stage of 'theoretical psychology', our concern is much the same as that of the cyberneticist or exponent of artificial intelligence. Only when further evidence from the direction of brain-science is forthcoming is the second stage complete when we are in a position to say that our theory tells us how the brain actually operates in these circumstances as opposed merely to how it might operate.
Lest we lose our sense of perspective at this point we should take note that this second stage has not yet been completed even with the most basic cognitive functions such as memory although, of course, there are scores of abstract theories as to how particular kinds of remembering might be mediated. It is no less important to recognise that all the dominant schools of psychology are reductionist in the aforegoing sense. This applies equally to those who now call themselves 'mentalists' or 'cognitive theorists' who use concepts like 'internalised grammars' etc. as it does to the hardened behaviourist who prefers to talk in terms of conditioning and to concentrate on overt performance. Chomskyans and Skinnerians alike share the assumption that the brain, as a physical system, possesses all the properties and structures necessary to actualise their theoretical suppositions.
Granted that the whole enterprise of a scientific psychology makes sense, it is hardly surprising that interactionism (often scornfully, if inaccurately, referred to as the homunculus theory of mind) should be viewed as a gross betrayal. For, if one starts from the assumption that how a person behaves depends, in part at least, on his having a mind that is endowed with certain unique properties and powers over and above those that belong to a conceivable physical system such as the brain, then one tends to end up explaining the behaviour in terms of those very powers of mind that one has invented, on an ad hoc basis, precisely to account for the behaviour.
This type of circular explanation, notorious in psychology, takes us back to the armchair theorists and faculty psychologists of the 19th Century. The only escape from this is to have an independent theory of mind, analogous to physics as a theory of matter, but this has so far eluded us, mind as such remains the densest of mysteries. The history of psychology has been largely, therefore, a revolt against interactionism which was identified with common sense psychology.
Fear of the homunculus has kept academic psychology firmly tied to the apron strings of materialism. Perhaps the one important school of psychology - if indeed one can describe it as a school - which acknowledged the autonomy of mind was Functionalism which flourished around the turn of the century. Its most illustrious spokesman, William James, took issue with the epiphenomenalism of Wundtian psychology or Kraepelinian psychiatry and argued that mind, like everything else in nature, must have a biological function. But his championship was not enough to turn the tide.
We have, it seems, reached a stalemate. Materialism, we may con cede, is more in tune with scientific thinking and more conducive to scientific research but, in all that concerns our humanity, there seemed little doubt that interactionism makes better sense. Unless, therefore, some fresh arguments were to make materialism intuitively more plausible or, alternatively, unless fresh evidence were forthcoming that would make interactionism scientifically more acceptable, which of the two command our allegiance may depend on whether our outlook is more influenced by scientific or humanistic considerations. While it is clearly impossible to anticipate what ingenious new arguments may yet be cast into the arena, there is already a body of evidence which, if it carried more weight, would seriously weaken the scientific plausibility of materialism. For there is One empirical implication which we have not so far mentioned which does distinguish between the two opposed positions. If mind is something distinct from the brain with which it normally interacts, then it is at least conceivable that it could, in certain circumstances, interact with other physical objects or systems. If, on the contrary, there is no distinction between mind and brain, inasmuch as mental processes are just a function of brain processes, then, clearly it makes nonsense to talk of the mind functioning independently of the brain.
Now it so happens that there is already what one can only describe as a vast amount of evidence which, if taken at its face value, would suggest that mind interacts on occasion, with external physical objects. I refer, of course, to parapsychology (Beloff 1974, 1977).
Although, in our present state of ignorance, parapsychology has to be defined in purely negative terms, i.e. as the study of those phenomena that cannot be explained in terms of accepted scientific principles, that is to say in materialist terms, conceptually, it could be thought of as concerned with those powers of mind that are irreducibly mental or non-physical.
According to this positive conception parapsychology could be defined as that part of psychology which deals with the mind-matter interface. At a more concrete operational level parapsychology is concerned with two particular phenomena:
(a) where an organism obtains information about events remote in space and/or time without such information being conveyed via any known physical channels, as is the case with normal perception
(b) where an organism influences events remote in space and/or time again without such an effect being transmitted via any known physical channels as is the case with normal motor activity.
(a) is known technically as ESP and (b) is known technically as PK and, collectively, the phenomena are known technically as PSI.
Although, as I have said, the evidence for PSI is extensive, much of it is of an inferior quality, some of it is definitely suspect and none of it is decisive. It is not decisive for one very good reason, there is as yet no PSI effect that can be demonstrated on demand.
Science cannot afford to relax the rule which demands that any new claim must be confirmable by those competent to test it. Whether PSI phenomena are peculiarly elusive or non-existent or whether we simply do not yet know enough about the conditions under which they occur to ensure their reproducibility, the fact remains that they cannot qualify as yet for inclusion into the body of accepted scientific knowledge. Nevertheless, when this has been said, the fact remains that one would need to be either very ignorant or very prejudiced or, better still, both to argue that the evidence is so derisory that it can safely be ignored in this context.
What the materialist must ask, therefore, is, assuming that the evidence is valid, does it necessitate an interactionist interpretation or could it in the last resort be reconciled with materialism? It is true that nothing so far known to brain-science would have led us to suspect that the brain, as a physical system, could communicate with objects remote in space, let alone in time, nevertheless one can never say that one is never in a position to say that all the physical possibilities have been exhaustively considered. Hence, however tempting it may be to describe PSI phenomena in terms of mind-matter interactions, alternative conceptualisations cannot be excluded.
Two developments within parapsychology would, I believe, upset the case for claiming this field as affording empirical grounds for the interactionist thesis. If it were possible to demonstrate ESP or PK using only computers or other appropriate artifacts or using only living tissue in vitro or even plants in lieu of a human or animal subject, in other words systems to which we would not normally attribute a mind, there would be little temptation left to think of such phenomena as a manifestation of mind. The state would be set for their eventual incorporation into an extended and revised physics and materialism and, with it, the unity of science would be vindicated. But if this does not happen and if, nevertheless, parapsychological claims become increasingly hard to ignore, then the case for interactionism would become more than just a metaphysical choice.
To avoid misunderstanding at this point, it should not be thought that the interactionist will have to propose certain paraphysical forces or energies to make up for the missing physical connections, as one often finds in the more naive parapsychological theories. It is much more plausible to suppose that the way in which mind and matter interact is different in kind from the way matter interacts with matter. There is a strong suggestion, which I cannot enlarge upon here, that, in PK for example, the effect is produced not by feeding additional energy into the target-system but rather by feeding in pure information so as to alter the probabilities of events at the microphysical level while leaving the overall energy of the system invariant. There is likewise a strong suggestion that PSI processes may be irreducibly teleological in their mode of action by which I mean that the end somehow dictates the specific means which bring about its fulfilment. But this takes us into the realm of speculation, critics might even say into the realm of magic.
For the present, and in all probability for a very long time to come, it must remain a matter of philosophical opinion whether mind is for anything, and, if so, what precisely it is for, or whether mind is merely an aspect of matter which, by the grace of nature as it were, happens to be associated with the workings of our brain. Psychology as we have known it so far could teach us only about the behaviour and experience of the unified psychophysical organism; it might be, however, that the mind-science of tomorrow, when paranormal as well as normal phenomena have been taken into account, will be able to return an unequivocal answer to the question of why we have minds at all.