JOHN LUCAS

The nature of mind has been of perennial interest to philosophers, both as one of the characteristic features of man and as a precondition of all thought. Man has long been described, or even defined, as a rational animal, and even now biologists will allow that it is by his intelligence that man is distinguished from the other animals. Men are not only intelligent, they are also conscious beings who have feelings and emotions, who form opinions and intentions, who talk with one another, and sometimes show forth originality as well as often taking decisions and taking up positions, and occasionally seeking after truth.

There is a tradition of argument that to think clearly about the universe we have to take into account the fact that mental phenomena exist and that this betokens the existence of a mind that created the universe. Even in the more critical approach to philosophy that has been in fashion since the time of Hume, philosophy has still been concerned to secure a rational assessment of the intellectual powers of man; it has sometimes even been defined as thought about thought. I wouldn't go so far as to define it as that, but at least as a philosopher I must own that every philosopher, from Socrates to the Schoolmen and from Descartes to the present, has been and must be profoundly concerned with the nature of mind both because it is this that is peculiarly characteristic of human beings and because it is with this that we think. This we must consider if we are to come to terms with ourselves as being ourselves not merely men but thinking men, rational agents who reflect upon their own powers and their own aspirations.

It is not only, however, one of the perennial problems of philosophy but also now the matter of much more general and topical interest, and it is this that has led us to choose the phenomenon of mind as the general topic of the Gifford Lectures. The reason for this lies with the scientists, biologists, and computer engineers. We are all now aware that computer engineers can construct machines which are able to simulate many of the apparently intelligent and peculiarly human activities which we have hitherto regarded as our own preserve. Physiologists, especially neuro-physiologists, and psychologists have from a very different point of view been pressing home their enquiries about the nature of mind and seeking to provide scientific explanations of what had hitherto been regarded as purely mental phenomena—one from which scientists should properly be excluded.

This has raised a number of problems and many people have felt that the development of scientific enquiry into the nature of mind has posed a threat to what we had hitherto regarded as the special preserve of morality and religion and the other things that we had held to be peculiarly human. And thus it is that we are at this time enquiring into the phenomenon of mind as something which is of concern from many different angles.

My own special interest in the nature of mind stems from my school-days when I was at Winchester and was listening to an essay by a much cleverer boy who was putting forward what he regarded as the scientific world-view, and maintaining that everything could be explained in terms of matter in strict categories of cause and effect. I didn't agree, but found it hard to resist his arguments till it occurred to me that the very fact that he was arguing with me and trying to secure my rational agreement to his position as being one that was true was itself an argument against the thesis that he was maintaining. The very fact that he addressed himself, as a rational agent, to me as another rational agent, belied his claim that everything could be completely explained in terms of the construction of his nervous system and the state of his endocrine glands.

When I went up to the University I pursued this argument further. I tried it on my tutor who immediately said that it was nonsense and that Russell's Paradoxes had shown that you couldn't ever hope to get an argument to bite its own tail, or to prove that another philosopher had sawn off the branch on which he was sitting. I was dismayed by this, although not entirely convinced, and then later heard of a very dim recherché mathematical theorem—Gödel's Theorem—somewhere near the foundations of mathematical logic, which seemed to do just what my tutor had told me I wasn't allowed to do. I pursued this argument and in the end I found a way of expressing in purely mathematical and logical terms the intuition I had had that arguments which cut off themselves from the branch on which they are sitting are in some way defective. I published this about ten years ago in an article and more fully last year in a book.

The conclusions were highly unwelcome to a number of people—I had the experience once at Massachusetts Institute of Technology of seeing an American frothing at the mouth, and it's often been maintained that I was morally very wicked to use metamathematical arguments to support moral conclusions. But although I have often been accused of wickedness and my arguments are highly unwelcome and many people disagree with me, ‘their witness agreeth not with one another’ and I am beginning to be fairly confident now that the argument itself cannot be faulted; not too confident yet—who knows what might not turn up? But I am beginning—I mean my fingers are not as crossed as they were. And I think that in traditional terms this would lead me to say that although clearly now I wouldn't put forward the argument in exactly the same terms as when I was seventeen, the whole idea of materialism has rather evaporated. It seems very much more ethereal than it used to be in the days of schoolboy Newtonian mechanics and hard massy point particles. Nevertheless I think I would still like for this purpose to classify myself as holding some traditionalist position. Let me describe myself as a dualist, not in the sense that Descartes was—I am not a clever enough philosopher to handle even one substance, let alone two—nor in the more fashionable way now, as Strawson is, a dualist of predicates rather than of substances—I believe that P predicates and M predicates are different, but I am not logician enough ever to discover what the logical relations between them are. Rather let me say that I am a dualist with regard to reasons, and one of the arguments I shall put forward is that there is more than one (at least two) different type of reason, different type of explanation, different way of understanding.

To put it crudely now, I want to say that there are different ways in which we understand and explain the actions undertaken by a rational agent, and events which are caused by definite external conditions or causal factors. And if I can make good this argument it will have very great consequences both for science and for morality and religion. The old conflict between science and religion and the new conflict between science and humanity will be resolved by our coming to understand science as being very much more complicated than some scientists have hitherto felt impelled to say that in principle it was. Note the qualifications. Scientists have often been alarmed or angered by the attitude of moralists and philosophers and theologians who have put up a ‘hands off’ sign around man and around the mind. They have felt that it was entirely wrong to say that these things are inexplicable, and I shall not say that, but only that they are inexplicable within an extremely limited, restricted, and Procrustean scheme of explanation. I think scientists themselves will admit when they come to reflect upon what it is that they are doing that it embraces not one but many different types of explanation. And although I shall certainly maintain, in contrast to some traditional philosophers, that we can have a scientific investigation of the mind, and hope to explain mental phenomena, such an explanation will be such as not to threaten the mind, not to threaten our idea of humanity; instead of explaining it away, it will expound it in a way which is entirely compatible with our normal intuitions of freedom and responsibility and creativity, and the other peculiar characteristics which we have hitherto associated with the mind. That is to say, it will lead to an enlargement of science rather than a reduction of mind.

This also will have great consequences for morality and for religion. It will reinstate what the moralists have long believed, the concept of an autonomous agent. We shall be able to explain men, we shall be able to explain their actions as the actions of beings who are themselves self-critical and who can make up their own minds what they are going to do. And it will also lead us to a very much wider understanding of the universe. We shall come (if we are to give a full understanding of the universe) to see it as to be explained not only in the rather limited categories which were put forward originally by David Hume, but with a much more generous idea of rationality and what it is to count as an explanation; that is, we shall reckon that if we are to give a full understanding of the universe, we must enlarge our categories of explanation and rationality to be able to accommodate the evident fact that there are minds which exist in the universe, and we shall explain these in terms of a wider view of rationality, which, according to the opening verses of St John's Gospel is but another name for God.

LONGUET-HIGGINS

It would be perverse to disagree with many of the things that John Lucas has said about the mind, and in particular his insistence upon its rationality as one of its essential characteristics. Nonetheless I feel dissatisfied with his philosophical approach, which seems to take us hardly any further towards a real understanding of the nature of mind. Not that there is anything shameful about old-fashioned methods of intellectual enquiry if one cannot improve upon them, but can we afford, in discussing mental phenomena, to disregard the lessons and insights which can be gleaned from modern psychology, logic and linguistics? Perhaps we could, if psychology were no more than the observation of people's behaviour, if logic were simply the idle manipulation of symbols, and if linguistics were no more than a sophisticated word game. And it must be admitted that some practitioners of these arts have done little to correct such impressions. But what inspired the founders of logic, psychology, and linguistics? The belief, surely, that the only way to advance in our understanding of the mind beyond the stage of metaphysical generalities was to attend closely to the actual phenomena which we take to be evidence of mental activity and to try to interpret these phenomena by the construction of models—or, if you prefer, of scientific theories. I use the word ‘scientific’ with caution because it may give a wrong impression, which I shall immediately do my best to dispel.

The word ‘science’ has had a chequered history. Originally, it was a synonym for knowledge or understanding, but it soon became a label for that part of our knowledge which was acquired by experiment or observation and could be fitted together into a logically coherent structure. Scientific facts not only had to be publicly verifiable: they had to be amenable to interpretation. And scientific theories not only had to fit the facts; they had to make assertions which were open to experimental disproof. Knowledge meeting these stringent conditions was found to yield enormous power over the natural world, and the word ‘science’ has now gained such emotional and technological overtones that its primary meaning has been almost forgotten. But it is the best word we have for describing the interpretation of natural phenomena, and I propose to use it in this sense in spite of the risk of misunderstanding. In short, I shall suggest that for coming to grips with mental phenomena metaphysical generalities are not enough. We must try to be as rigorously scientific in our approach to the problems of mind as to the problems of matter.

Again, there will be misunderstandings unless I try to forestall them. Only the most simple-minded scientist, it will be asserted, can believe that it is possible to do science without making any metaphysical assumptions, and his science will inevitably be coloured by his metaphysical presuppositions. There are various possible replies to this criticism of science without metaphysics, or at least without an explicit metaphysic. One is to point to the wide agreement between scientists of entirely different cultural backgrounds on both experimental and theoretical issues. Another is to observe what happens when scientific theories are called in question on metaphysical grounds. Four examples come to mind. Wilberforce's attack on Darwin's Theory of Evolution ended in a rout. The attempt by Lysenko to re-establish, on quasi-Marxist principles, the inheritance of acquired characteristics did untold damage in Russian biology. Metaphysical preconceptions about the essential distinctness of space and time have obstructed, and still obstruct, a clear appreciation of what is asserted in the theory of relativity and have even led some intransigent philosophers of science to question the integrity of their scientific colleagues. And fourthly, the Quantum theory, which underpins the whole of physics, is still being sniped at because its laws, though they have survived the most searching tests, remain uninterpretable within metaphysical schemes which insist on the objective reality of all physical situations.

To put the matter in this way is to oversimplify, insofar as the construction of scientific theories is a never-ending process involving assertions which at one time may seem to be merely metaphysical but later are seen to hold empirical implications. And nothing in science could be more provisional at the present time than our ideas about the mind and how to study it.

Tomorrow afternoon I shall indeed be severely critical of some present scientific thinking about mental phenomena and will suggest that there are some serious categorial confusions which at present bedevil the study of the brain, which is the seat of our own mental activity. Indeed, I would not be taking part in these discussions unless I felt, with the other participants, that we are very unlikely to achieve a better understanding of the mind without a thorough examination in philosophical terms of the concepts that will be needed for building a properly scientific theory. But of one thing I feel certain: we shall not succeed, nor will others, by taking up fixed metaphysical positions in advance. By all means let us attempt to state as clearly as we can those issues to which we feel that a theory of the mind must address itself, and until we have a satisfactory theory these issues will have to be couched in the language of philosophy rather than in the language of science. And by all means, if we can, let us look around to see whether there are any overriding limitations to which any theory of the mind must conform. Perhaps, as John Lucas will later argue, the undecidability of arithmetic puts paid to a particular type of psychological theory, though I very much doubt it. But if there are any limiting principles of this kind to be discovered, then their discovery promotes them from the realm of metaphysical prohibitions to the status of scientific assertions, and they become part of psychology in its proper sense.

To me, the most significant question about the mind is ‘How are we to set about constructing a satisfying theoretical account of mental phenomena?’ I suppose that each one of us is expected to show his hand on this occasion, if only to raise expectations of what disputes are likely to arise between us. I, for better or for worse, am professionally committed to the study of cognitive processes. The question has actually arisen in this university as to whether my colleagues and I are psychologists or not. The issue is confused by a schism in psychology itself. Is it legitimate for a psychological theory to include ‘subjective’ concepts such as motive, decision and interpretation, or must psychology be limited to the discussion of overt behaviour in terms of measurable stimuli and responses? If the latter, then cognitive psychology is a non-subject and I am a non-scientist. Naturally, I like to think otherwise. But then the question arises: in what form are we to cast the theory of mind which has room for genuinely mental phenomena? Freud made a serious attempt to do this, and though his theories certainly lacked mathematical precision, perhaps mathematical precision is not everything. But in this second half of the twentieth century the engineers and mathematicians have presented us with a machine which challenges us to think in a new way about our intellectual processes—the electronic computer. If we can ask and answer questions about how computers do arithmetic, why should we not ask the same questions about ourselves, and hope ultimately for as detailed an answer? And if the question can be asked about arithmetic why should we not ask it about our less pedestrian intellectual activities? It would be sheer negligence not to see what light can be thrown on the nature of mental processes by comparing them with the various steps in a computation; and this, in my opinion, is by far the most interesting possibility which the computer has opened before us. To do so is not to make any extravagant claims for computers or to blaspheme against the humanity of man. Not to do so would be a far worse insult, suggesting that we human beings could not stand critical comparison with our own inventions.

KENNY

Longuet-Higgins has just said that philosophy cannot take us very far in the study of the mind. The question must have occurred to many of you ‘what can philosophy have to say at all about the phenomenon of mind?’ In the nineteenth century, when philosophy in these islands was dominated by the spirit of Hegel, the answer might well have been ‘everything’. Philosophy consisted essentially of logic and metaphysics. Logic was the study of the laws of thought and metaphysics was the understanding of the universe as the evolution of spirit. In the present century, since experimental psychology has become an independent discipline, the answer which springs to mind is likely to be ‘nothing’. Mind as spiritual entity has been exploded. The study of mind, if it is not to be superstitious mystification, must be either the study of behaviour or the study of brain. The study of behaviour is best done by the psychologist and perhaps the sociologist; the study of brains is for the biochemist and neurophysiologist: in neither area is there any scope for the arm-chair intuitions of the philosopher.

Now if either of these views were true there would be no room for the four of us on this platform. If the Hegelian view were the true one then John Lucas and I should have it to ourselves; if the contrary view were true we shouldn't be here at all. I believe that the truth lies between the two extremes, so that we can all sit down together.

I'd agree with Longuet-Higgins that metaphysical generalities will not take us far, though I am not quite happy with Lysenko and Wilberforce as the spokesmen of metaphysical generalities. But I'll try to explain what I think is the true role of the philosopher in these matters. It is certainly not the thing that Longuet-Higgins dislikes most, the taking up of metaphysical positions in advance of the evidence.

In the last century not only psychology but also logic has set up house independently of philosophy. It has become highly mathematical. Its contemporary practitioners no longer think of it as the study of the laws of thought, if by laws of thought we mean natural laws which govern our thinking in the way in which Newton's laws govern motion. If we are to think of the truths of logic as laws at all, the laws to which we should compare them are the laws which regulate the operation of traffic—laws which notoriously differ from those which describe the actual behaviour of traffic. We differ from the Hegelians, then, over the nature of logic. Few philosophers today would accept a Hegelian metaphysic either. Few, I mean, would see the study of the world as a whole as the study of the manifestation of mind. Some philosophers, of course, continue to believe that the world was created by God and in that way is a product of intelligence. However, I think even theistic philosophers would not wish to rest their claim to contribute to the study of the human mind on their theistic beliefs alone. What then do philosophers have to contribute, and on what is their contribution based?

It's a familiar jibe that philosophers only say what everybody knows, in language that nobody can understand. Now I think that it is true that the starting point of philosophy is what everyone knows, but it is a well-known fact that half of what everyone knows is true, and the other half is false. The aim of the philosopher is to give explicit and precise formulation to our common, informal, hazy, vital and passionate beliefs about ourselves and about the world in such a way that we can coolly and self-consciously sort out the truth from the prejudice in what we all know. Styles and methods of philosophy differ from age to age, but I think that this job is clearly the common aim of the question-and-answer games which Socrates used to play, of the metaphysical doubtings of Descartes and of the investigations into everyday idiom which until recently used to be the common practice of philosophers at Oxford.

Now in the particular area of philosophy of mind it is particularly important to make explicit and criticise what we all believe we know. Our intuitions about fundamental physics are not likely to be at all strong and they are almost certainly of no value, but when we turn to the study of mind we turn to an area in which we are all convinced that we have a special title to speak. If I don't know what the contents of my own mind are (each of us feels) then who does? Few of us claim to be any sort of expert in any of the sciences of mind, but each of us feels that even if he is not in possession of the expertise of the science of mind at least he is the intimate and irreplaceable custodian of its data. To sort out what is true from what is false in this conviction is itself one of the central tasks of the philosophy of mind. It seems to me that it is a task to which experimental psychology, too, cannot be indifferent.

One way in which men have tried to express their special relationship to their own minds is this. Each one of us, we feel, has in addition to his public bodily history another inward life in which there occur events which are private to him, of which he alone is a witness, and of which others can know only by his testimony. This position is often called a dualist position, since it regards body and mind as two distinct entities. Many people, I think, would say that that's just what the word ‘mind’ means, namely a private and inward realm of this kind, and they may say this whether they are dualists who affirm the existence of an inner realm or they are behaviourists who deny the existence of mind.

Now I believe that this supposition is incorrect and has been shown to be such by the patient work of Wittgenstein. His later philosophy of mind I take to be one of the most interesting philosophical events of the century, and the importance of his work is that it shows a third way between the unacceptable alternatives of dualism and behaviourism. According to the dualist, the relation between mental processes and their expression in behaviour is a contingent relation; it is not any sort of logical necessity. Mind and body are separate; each of them could in principle live its life independent of the other. For the behaviourist, on the other hand, if he is prepared to give meaning to the word ‘mind’ at all, then the relation between mind and body is in some way a necessary identity—all ascriptions of mental attributes to human beings, if they are not to be mere myth-making, must be reducible to ascriptions of bodily behaviour whether actual or hypothetical. Wittgenstein argued against both these schools of thought. He thought that bodily behaviour was neither identical with, nor merely contingently connected with, the mental life of which it is the sign. Bodily behaviour isn't identical with mental life; it is only the sign of it, it is only evidence for it. But this evidential relation is one which is built into the meaning of the mental predicates which we use of human beings; it isn't something which is discovered by induction and experiment.

From this point of view both dualism and behaviourism share a common false presupposition—namely that of the essential privacy of mental events. The dualist argues like this: mental events are essentially private; science cannot study what is essentially private; therefore there can be no science of mental events. The behaviourist argues: science can study the whole life of man, science cannot study what is essentially private; therefore the life of man does not include mental events. Both conclusions, I think, are false; both arguments depend on one true premise—namely, science cannot study what is essentially private—and one false premise: mental events are essentially private. Wittgenstein's merit was to show that the second premise was false and the true premise was harmless. The reason why science cannot study what is essentially private is that the essentially private is a piece of philosopher's nonsense.

This then is the first way in which the philosopher can hope to contribute to the study of the phenomenon of mind. Philosophy of mind can help to sort out what is the truth and what is the muddle in what we all think we know about our own minds. Though this is not an empirical investigation it is not a matter of indifference to the empirical investigator, for it concerns the correct identification and description of the data which he hopes to systematise and explain. However, it is not only the philosophy of mind but also the philosophy of language which can cast light on the phenomenon of mind. For if we are to study the nature of mind by studying its manifestations in behaviour, it is clear that the study of linguistic behaviour will be of paramount importance in the investigation of specifically human intelligence. If we look on human beings as systems whose output is to be explained in terms of input and internal organisation, the most important part of that output will be the linguistic output, and if we are to begin to account for the output we must be clear about its nature. And here again recent developments in philosophy can help, for along with the development of formal logic and the re-invigoration of philosophy of mind, the greatest progress in philosophy in recent decades has been in the philosophy of language.

For the past decade and more, philosophers and experimental psychologists have both been studying, with a growing degree of mathematical sophistication, the syntax and semantics of natural languages. During this period their work has brought them closer and closer together on terrain which was traditionally occupied by the linguist. No doubt the philosopher approaches this area from an a priori viewpoint and the psychologist from an experimental one. But in this area the boundary between conceptual and empirical elements is more than usually difficult to draw. In a later lecture I hope to offer some suggestions as to where it should be drawn. But the difficulty of drawing it makes the philosopher still indispensable to the study of man as a language-using animal.

But is it after all only the use of language which makes man unique—if he is unique? If linguistic intelligence is merely the ability to carry out formal operations of a certain complexity, for instance the parsing of sentences or the proof of theorems in a formal system, then it seems clear that linguistic intelligence is a comparatively unimportant part of humanity and that it is shared by inert artifacts like computers. It is rather in the interpretation of formal systems, their application to the world and to our concerns, that we really display the powers of mind, and from this point of view formal systems are simply games we play and tools we use. Computers, like Humean reason, are, and should only be, the slaves of our passions. Where they fall short of human beings is not so much in lacking intelligence but in lacking passions. Of course, reason itself includes more than Hume thought; rationality involves not only powers of the intellect but attitudes of the will. To be rational is to be capable of acting for reasons, and reasons include both cognitive and affective factors—purposes as well as information.

If I had to single out what makes man unique I would even today want to start from Aristotle's definition of man in the Nichomachean Ethics—where he defines man not as a rational animal but as a choosing agent, that is to say an agent whose actions are the result of willing wedded to thought and thought wedded to will. By will Aristotle meant decisions based on long-term goals which were self-selected. It is this, it seems to me, which computers lack. Only an agent such as Aristotle describes is capable of conferring meaning on formal systems, is capable of making signs into symbols. For meaning cannot be defined without intention and knowledge and the operations of non-living hardware only have meaning because of the intentions of their human agents. That is a thought which I hope to develop next week.

What Aristotle's definition leaves out, it seems to me, is the element of creativity. Creativity seems the third principle characteristic of the human mind, besides intelligence and rationality. Creativity is the hardest to define and I shall not attempt to do so—but in some ways it is the most important. For we share linguistic intelligence with computers and we share passions and purposes with other animals, so that if the Aristotelian account is adequate then we differ from animals only because of what we share with computers, and we differ from computers only because of what we share with animals. Creativity is the characteristic which, if any does, separates us both from inert artifacts and from brute beasts.

WADDINGTON

The previous three speakers have outlined—illuminated—the stage on which most of our discussions of the human mind are going to take place, largely in the context of linguistic expression and by comparison with some of the performances of computers. They are all professional students of these topics: two professional philosophers, one professional—well, he wasn't quite sure whether he would allow himself to be called a theoretical psychologist or what. But I am afraid I am speaking from right outside this topic. I am not a professional student of the human mind at all. I am a straight biologist. I think my function here is, to provide—or at least suggest—some of the background, let me call it, against which the human mind can, and I think should, be seen.

One must first ask ‘In what circumstances would we use the word “mind” in biology?’ Any circumstances that would suggest that we should use it would certainly involve an animal behaving in some way in response to certain inputs of stimuli. If its behaviour was an exceedingly simple reaction to a stimulus, such as for instance a knee jerk when you hit the right tendon, I think we wouldn't want to use the word ‘mind’. We are tempted to use the word ‘mind’ when we know that something is going on in the nervous system and that it is something very complex. Perhaps it need not necessarily be only in the brain, but in most of the higher animals it is mainly in the brain. When things go on in the brain stem, I am not certain whether we would be tempted to call them ‘mind’ or not.

So, in the first place, I am making the point that there is an area of indecision as to what things we would include in the ‘mind’, and what things we would not.

Granted that there are some very highly complex phenomena in the central nervous system which we might be tempted to call ‘the mind’, can we go any further than that? First of all, I would like rather to rule out, for purposes of this discussion, the idea that we can deduce much about the nature of these complex phenomena that we call mind from our understanding of the processes of evolution by which they have been produced. We realise, of course, that the higher organisms have been brought into being by evolution, and that it is evolutionary processes which have shaped their physical being and their mental apparatus. But, in my opinion, our knowledge of the theory of evolution is very very much less than is usually alleged, and is certainly not enough to enable us to deduce anything much about the nature of the mind. Any very complex process in animals, such as we have said that mind must be, must depend on a very large number of hereditary factors. It can perhaps be stopped by an inappropriate signal, an inappropriate factor, in the animal's hereditary constitution, but it cannot be created by any single factor—it must depend on the interactions of a very large number of factors. Merely to say that this aspect of the animal's physical or mental constitution is determined by its heredity doesn't really tell you anything very interesting about it. It is like saying it is made up of atoms. Of course—so what?

Another analogy one might use is that the individual genes determining the heredity of an animal may perhaps be compared to the stones forming the aggregate in a concrete structure. You can't discuss much of the difference between a concrete building by Corbusier and Candela, say, by discussing the aggregates they used in the concrete. Of course, the aggregates are absolutely essential—they could not get along without stones in the concrete—and if some of the stones are really made of weak clay it will make a defective structure, and so on. But the things you are really interested in in the buildings are not dependent on the aggregate, but on properties of the much larger members into which the aggregates are formed. The same thing seems to me to be true of the complex organs of higher organisms, and certainly true of such complicated phenomena as the mental events which we call ‘mind’.

Similarly, simply to say that a certain type of output from an animal is ‘instinctive’ doesn't add anything much to a discussion of mind. In an excessively simple instinctive action, when an animal simply responds in a defined way to a defined stimulus, one might say there is very little mental activity involved in that. But other types of instinctive behaviour involve much more complex outputs. For instance, consider a bird building a nest—if you take a bird that builds a nice complex nest, like a weaver bird, say, that is instinctive behaviour; birds of one species will always build a nest of a certain pattern. But it must be a highly complex nervous activity, as you will realise if you imagine youself approaching a nest, carrying a piece of straw in your beak, and trying to decide how to weave it into the nest. This is, it seems to me, behaviour worthy of being called mental, although it is also ‘instinctive’.

Can we say that mental behaviour must always be conscious behaviour? This raises the question which Kenny was speaking about, of the private world of consciousness—I don't want to argue at the moment just how private the world of consciousness is—it's certainly pretty private as between myself and the chimpanzee or dog or cat. I just can't tell what, if anything, they are conscious of. I am going to suggest that from the biological point of view of mind consciousness is not necessarily terribly important. Nearly everything that we usually do with conscious thought, we can actually do, without conscious thought. For instance, we are not normally conscious of the very involved mental nervous events that must be going on controlling our movements. Even in some of the higher forms of movement: can one really say that a concert pianist is actually conscious of putting down particular fingers on particular notes when he is playing a fast passage? Or is a good ball player really conscious of exactly what he is doing to that ball? It seems to me in neither case is he fully conscious. He is conscious that he wants to produce a certain effect, and he is conscious of the effect he is actually getting, but not conscious of the actual nervous steps, or even the physical steps, involved in the process. Similarly, as we all know, many people have said that some of their major discoveries, of a really creative kind, have as it were leapt into their mind after a good night's sleep, or something like that, but they have not been conscious of the mental processes by which they worked out what eventually turn out to be highly complex and logical structures.

And this comes out also, I think, if we consider the relation of language to mind. Now we are certainly going in the next few days to have a great deal of discussion of language in this series of lectures, and I think we will find—I am not a professional in this field—that the analysis of language has given us a lot of clues to the ways in which mental processes may be working. But I think the mental processes can often work without the language; the language may be indicative evidence, but it is not, I should suggest, a necessary part of the process. I would like to quote what Einstein once wrote about his thought processes. He said: ‘The words of the language as they are written or spoken do not seem to play any role in my mechanism of thought. The psychical entities which seem to serve as elements in thought are signs and more or less clear images which can be voluntarily reproduced and combined. The above-mentioned elements are, in my case, of visual and some of muscular type. Conventional words or other signs have to be sought for laboriously only as the secondary stage, when the mentioned associative play is sufficiently established and can be reproduced at will’. That is the testimony of a very profound thinker, saying that language is not necessarily the accompaniment of activities which one is bound to call mental. The biologist is essentially interested in another question that has also been raised, particularly by Longuet-Higgins, I think; when can mental activity be said to be intelligent?

Activity can be mental without necessarily being intelligent. I think what one means when one calls the activity intelligent is that it produces some successful result; and by ‘successful’ the biologist would, in the first place, think of success in terms of natural selection. Now natural selection is a much more complex process than is usually suggested by elementary discussions of biology. They often confine it to ‘leaving a lot of off-spring’. Now leaving a lot of off-spring is quite a successful thing to do in some cases, but not if you leave so many that you eat yourself out of your hearth and home, as the human race seems to be in some danger of doing at the present time. Natural selection is really concerned with selecting things which have long-lasting stability—which can go on lasting for many, many generations. It is quite a complex topic, to which I shall hope to return in a later lecture. But in biology, then, intelligent behaviour would be behaviour that is successful in achieving one of the objectives of the organism concerned. You cannot define intelligence without bringing in a reference to a goal or objective. In nature such goals and objectives may be set up by the operation of natural selection, and they may be quite complex; we will discuss later what some of those complexities are. But, of course, man has certainly the possibility not only of having his goal set for him by natural selection, but of defining and setting his own goals. How far other animals can do this is not quite so easy to say, but I think we could certainly assert that man is capable of setting his own goals and this settles what he means by ‘intelligent’.

Is this, perhaps, the essential distinction between mankind and the computers, of which we are going to be told in more detail? Normally man sets the goals for his computers. He fixes his computer to carry out operations, working on inputs similar to the language inputs to his own mind, and producing an output related to some goal that he has set the computer to do. If that were all that computers could ever do, then they would always be the slaves of human passions—to use Kenny's phrase. And there would be an absolute distinction between mankind and his artifacts in that man sets his own goals and he sets goals for his artifacts. I am, however, sufficient of a believer, if you like, in ‘natural theology’, which I think is the subject of the Gifford Lectures, to be not quite certain that computers couldn't conceivably do something better than that. I tend to believe that the goals of mankind are not arbitrarily invented but are actually inherent in the nature of the universe. I don't say man has really succeeded very often in finding them, but it seems to me that his great endeavour is the attempt to discover what goals are fixed by the nature of the universe, and the nature of himself living within it. If this is so, then it is not inconceivable that a computer equipped with sense organs and so on, could examine the world as we examine the world, and deduce from it the same sort of goals that we deduce from it. It would seem to me that if you could get a computer to do that, and only if you could get a computer to do that—to examine the world and to formulate for itself appropriate goals which would in effect be the passions that Kenny was referring to—only if it could do that could you really say that computers had become intelligent.

Now I leave this as a challenge to Longuet-Higgins. If he thinks he is ever going to be able to assemble such a computer, I think he would probably like to postpone the date for its birth some little time into the future.