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Lecture VIII: Mechanistic and Biological Psychology

Mechanistic interpretations of conscious behaviour do not seem to have been either so ancient or at any time so widespread as animistic interpretations. Yet we find a mechanistic interpretation outlined clearly in the philosophy of Democritus, side by side with a similar interpretation of the inorganic world. Sometimes, also, the animistic conception of the soul has gone so far in conferring upon it material attributes that it is somewhat hard to distinguish the animistic from a mechanistic interpretation; or conversely the mechanistic has come rather near to an animistic interpretation.

In mediaeval and modern times mechanistic interpretations of conscious behaviour have been to a large extent suppressed or driven below the surface by ecclesiastical or State authority. The mechanistic interpretations were commonly associated with atheism; but this was by no means always the case. Some forms of theology have, at any rate, come very close to mechanistic interpretation in their deterministic conception of human behaviour; and even the very orthodox Dr. Paley, in presenting the conception of God as the great Artificer, came pretty near to a mechanistic interpretation.

When we read the De Homine of Descartes we cannot but be struck with how close he had come in this particular book to a mechanistic interpretation of conscious behaviour, though other writings of his were quite inconsistent with such an interpretation. If we assumed that the mechanical processes by which the “animal spirit” was supposed to be separated off in the brain, and the valves to be opened on suitable occasions, were accompanied, but in no way affected, by consciousness, we should have a mechanistic conception of conscious behaviour.

In the eighteenth century we find in France, just before and during the period of the Revolution, a full-blown mechanistic conception in the writings of La Mettrie and others; and since then this conception has become more and more popularized. Among the influences which have contributed to this popularization we may count the waning influence of orthodox theology under the stress of historical and other criticism, the mechanistic movement in biology, the emergence of a belief in evolution, and the great practical successes which have resulted from the applications of physical and chemical science to the uses of mankind. These successes have by themselves produced a popular vogue among credulous persons for mechanistic interpretations.

On the philosophical side mechanistic interpretation could lean for support on the philosophy of Kant. If, owing to the nature of our perceptive faculties, it is impossible for us to perceive anything but phenomena capable of physical and chemical interpretation, it follows at once that all our interpretations of visible and tangible conscious behaviour must be mechanistic. This was in fact the position taken up by Lange in his History of Materialism.

If animism is the counterpart to the Newtonian conception of visible and tangible reality, it is equally true that a mechanistic conception of conscious behaviour is a natural revolt from animism. The mechanistic interpretation of conscious behaviour appears at its strongest and best when it is pitted against animism, just as the mechanistic interpretation of life appears at its best when it is pitted against vitalism.

Let us try to see what the mechanistic interpretation, as commonly applied, amounts to. In the first place, it makes no attempt to give any physico-chemical explanation of the fact of consciousness. It simply treats consciousness as a completely mysterious accompaniment of physiological phenomena which occur in the central nervous systems of higher animals. Any physico-chemical explanation of this accompaniment is expressly disclaimed. It is true that one enthusiastic mechanist affirmed, early last century, that the brain secretes consciousness, just as the liver secretes bile. Bile is, however, something visible and tangible, while mere consciousness (treated as an accompaniment of material activity) is not. Hence there is not, so far as we know, any meaning in saying that the brain secretes consciousness, nor is any such assertion needed for the mechanistic interpretation of conscious behaviour.

This point being made clear, it is easy to understand the basis of the mechanistic interpretation. That basis is the now easily demonstrable fact that every element which we can distinguish in conscious behaviour is dependent on what are ordinarily regarded as physiological or physical conditions. In the previous lecture I have already referred to this fact; but perhaps some expansion of the evidence for it may be added at this point. Let us first consider some of the conditions on which consciousness and rational behaviour depend.

Consciousness and the power of voluntary movement are immediately lost in man if the supply of arterial blood to the brain is cut off, as when the heart ceases to beat or a serious wound in the neck or chest allows the arterial blood to escape. Immediate fainting is rapidly followed by death if the blood supply is not restored. An exactly similar result follows if the blood supplied by the heart to the brain is not oxygenated. We have only to take three or four deep breaths of pure nitrogen or hydrogen (so as to wash out nearly all the oxygen in the lungs and in the venous blood normally returning to them) in order to produce complete loss of consciousness and paralysis of voluntary movement. If the oxygen supply to the lungs is now restored again immediately, consciousness and power of voluntary movement are again restored as rapidly as they were lost. The disappearance and reappearance of consciousness are just like the extinction of a piece of flaming and glowing coal when it is placed in pure nitrogen, and its relighting when it is restored to air before it has lost too much of its heat.

If now, instead of completely cutting off the supply of oxygen to the lungs, we gradually reduce the proportion of oxygen in the air breathed to a little less than half, we produce a marked deterioration in mental powers. The senses become dimmed, and what are ordinarily painful stimuli, such as those produced by a burn, may not be noticed at all. Power of memory of anything happening at the time is greatly impaired; behaviour becomes incoherent and irresponsible; and power of co-ordinated muscular movement is markedly diminished. It is thus quite evident that conscious behaviour of a normal kind depends very directly and immediately on a normal supply of oxygen to the brain.

But this is only one of a host of conditions which are now known to determine conscious behaviour. The oxygen supply to the brain is particularly open to exact investigation, thanks largely to the facts that it can so easily be interfered with, and that impairment in the normal saturation of the arterial blood with oxygen is accompanied by a striking change in its colour; but the regulated supply of other components of the blood, and so far as we know of every normal component except gaseous nitrogen, is, in the long run equally important, directly or indirectly, in the maintenance of conscious behaviour. Some of these components are present only in excessively minute proportions, and yet this minute proportion must be maintained. For instance, an increase of about 1 in 20,000 million parts in the proportion by weight of ionized hydrogen present in the brain appears to be sufficient to produce loss of consciousness.

Minute proportions of specific substances produced in other organs than the brain are now known to play an essential part in determining normal behaviour. Perhaps the classical instance of this is the specific iodine-containing substance formed in the thyroid gland and quite recently synthesized artificially outside the body. The absence or insufficient supply of this substance leads to a well-known form of idiocy. We can on general grounds be quite certain that the maintenance of normal cerebral structure and normal conscious behaviour depends on a supply of all sorts of substances brought by the blood to the brain from all other organs of the body, as well as from the external environment.

Equally important for conscious behaviour is the proper maintenance of the energy, potential or kinetic, reaching the brain. Heat is one form of kinetic energy; and if the temperature of the brain becomes too low or too high, conscious behaviour is impaired or annulled: nor can it be maintained without a proper supply of the potential energy contained in the food material and oxygen reaching it. If, moreover, the energy reaching it in the form of afferent stimuli from all parts of the body is not properly regulated, conscious behaviour becomes impaired. Every voluntary movement is guided to a greater or less extent by afferent stimuli from all parts of the body, including organs of the special senses and the semi-circular canals.

If now we consider the origin of the brain itself and of its characteristic behaviour in conscious experience, we find that both structure and behaviour are inherited from previous generations through germinal elements which exhibit no sign of consciousness. We can trace this inheritance backwards towards lower forms of life, and by inference to what we call inorganic material. Thus in every direction there is, it may be argued, the clearest evidence in favour of a physico-chemical determination, and consequent mechanistic interpretation, of conscious behaviour.

In previous lectures I have already, to some extent, discussed and rejected the mechanistic conclusions. The evidence only seems convincing if we make the initial assumption that the Newtonian interpretation of visible and tangible reality represents that reality satisfactorily, so that when, for instance, we speak in the Newtonian sense of matter and energy, time and space, our concepts of them correspond with reality. This correspondence was, we found, assumed by both mechanists and vitalists in the interpretation of mere life, and is assumed by both mechanists and animists in the case of conscious activity. The difficulties into which the assumption leads have already been discussed in the case of life. Let us now consider the difficulties into which the assumption leads in the case of conscious behaviour.

The conception of the soul is a conception, as we have seen, devised to account for the outstanding fact that each element in conscious behaviour expresses itself as belonging to a whole. As has also been pointed out in Lecture VI, the wholeness of conscious behaviour is limited neither in space nor in time. If, in all innocence, we treat its elements as existing separately from one another without a “meaning” which binds them together, we have simply ignored what is characteristic of them. What we interpret as the action of molecules of oxygen on the brain substance is a separate event in space and time, as is the response of what we interpret as the brain substance. No process of addition of such separate events will ever afford us the remotest conception of what we see and experience when we see and experince conscious behaviour. We certainly see something when we see a living body with all the signs of conscious behaviour absent in a person who breathes pure nitrogen for a short time, or when we see a dead body; and we can interpret the perception of the dead body fairly satisfactorily by means of mechanistic conceptions corresponding to the Newtonian “philosophy.” But we cannot connect the something which we seem to see with what we seemed to see in the conscious behaviour of the person. We are tempted to join up our broken experience by saying either that there is a soul that has left the body temporarily or permanently or has become paralyzed in some way, or else that there is really no such thing as a soul, but only a brain of which the normal activity is accompanied by an impalpable something called consciousness.

It is the latter alternative which I am considering in the present lecture, after rejecting the first alternative in the previous lecture. The second alternative is in every way as unsatisfactory as the first. Let there be no mistake. The difficulty does not concern an invisible and impalpable something called consciousness. If this were all the source of difficulty we could regard consciousness as an imponderable secretion, or as an impalpable accompaniment of all physical action. The difficulty concerns visible and palpable conscious behaviour. This behaviour is utterly different in kind from what we interpret as the behaviour of oxygen molecules and brain substance. The molecules, as we interpret their behaviour, do not act as part of a whole which extends over its spatial relations; nor do their actions represent a whole which expresses progressive continuity in its time-relations. Their behaviour as actually interpreted in accordance with physical principles thus throws no light at all on conscious behaviour. To suppose that it does is simply to ignore the character of the phenomena under discussion, and is thus very bad science.

We are, therefore, if we insist in adhering to the Newtonian conception of visible and tangible reality, buffeted backwards and forwards between animism and a mechanistic interpretation. Neither interpretation corresponds with our experience nor is in any way satisfactory as a scientific working hypothesis in the Interpretation of conscious behaviour, though either hypothesis may be used so long as we do not attempt to come to close quarters with what we are observing. If, however, we adopt the animistic hypothesis, we seem to leave the field clear for the application of the Newtonian conception to all that is outside the immediate influence of the soul or the vital principle, and to have comfortably shelved the difficulties which arise over mechanistic interpretations of conscious behaviour and life. It was thus very natural for Newton himself, as it has been for most physicists and chemists, to accept animism. At the present time, owing to the completely mistaken impressions which are prevalent as to the practical success of mechanistic interpretations of mere life, the tendency is rather to accept the mechanistic interpretation of conscious behaviour, or at least to suspect that it is probably correct. When, however, we come to close quarters with the mechanistic interpretation, it turns out to be totally unsatisfactory, since it simply ignores the character of what has to be interpreted.

Intermediate between mechanistic and animistic interpretations of conscious experience there is another mode of interpretation, which I shall call the biological interpretation. This is represented to some extent in the writings of Leibnitz, Bergson, and other philosophical and scientific authors; but I think that it has been given by far its most developed and clear-cut form in the remarkable recently published book by General Smuts on Holism and Evolution. In this book it is pointed out quite clearly that mechanistic interpretations of life are inconsistent with observation of life, owing to the fact that in the life of an organism the details of structure and activity express the existence of a whole, apart from which these details cannot be either described or understood. Throughout the book the treatment of Reality is made consistent with the fact that the existence of wholes is discernible, not merely in connexion with life, but also, though to a less developed extent, in the inorganic world, and by far most clearly of all in human personality.

It seems to me that the great advance in this book is that for an unintelligible élan vital or unconscious mind there is substituted an intelligible conception of a wholeness which is present in various stages of realization throughout the universe, though at first sight it appears on superficial examination to be absent in the inorganic world, with the result that the inorganic world appears to be mechanically determined in accordance with Newton's conception. The fundamental significance of the newer conceptions in physics is clearly pointed out in this reference.

The book is so much in accord with the conception of life as developed in the first five lectures of this course, and less fully in previous writings of my own, that I am sorry not to be in agreement with part of its conclusions. The point of difference is in General Smuts's treatment of personality. His book is written from the standpoint of organic evolution as a process of separable events, and he treats the evolution of personality as a similar process, continuous with the evolution of less highly developed wholes, as seen in the inorganic and lower organic worlds. This treatment seems to him to be necessary.

“Where,” he asks, “was the Spirit when the warm Silurian seas covered the face of the earth, and the lower types of fishes and marine creatures still formed the crest of the evolutionary wave? Or going still further back, where was the Spirit when in the pre-Cambrian system of the globe the first convulsive movements threw up the early mountains which have now entirely disappeared from the face of the earth, and when the living forms, if any, were of so low a type that none have been deciphered yet in the geological record? Where was the Spirit when the Solar System itself was still a diffuse fiery nebula? The evolutionary facts of Science are beyond dispute, and they support the view of the earth as existing millions of years before ever the psychical or spiritual order had arisen; and what is true of the earth may be similarly true of the universe as a whole. The fact that we have to grasp firmly in connexion with creative Evolution is that, while the spiritual or psychical factor is a real element in the universe, it is a comparatively recent arrival in the evolutionary order of things; that the universe existed untold millions of years before its arrival; and that it is just as wrong for Idealism to deny the world before the arrival of Spirit, as it is for Naturalism to deny Spirit when eventually it did appear in the world.”

It seems to me that in putting these questions and arguing in this way, General Smuts has forgotten a previous question which was put by Kant, himself the author of a nebular theory of the origin of the solar system. That previous question concerned the nature of time. From an analysis of conscious experience he drew the conclusion that time can only be a form in accordance with which, owing to the nature of Mind, our conscious experience is arranged. In other words, time is part of Mind, so that in the remoteness of Newtonian time Mind or Spirit is still present, and we have not passed outside of its wholeness.

In my sixth lecture I endeavoured to develop Kant's argument still further by pointing out that the wholeness which is expressed in conscious behaviour, whether that behaviour is called perception or voluntary response, is a wholeness which includes order in time as well as order in space, since conscious behaviour expresses both retrospection and anticipation. Temporal as well as spatial order is thus part of the wholeness. The separation implied in mere abstract time in the Newtonian sense has thus no meaning for conscious behaviour, any more than the separation in mere abstract space. The order of time as well as space is thus just a part of the expression of the spiritual whole which is embodied in conscious behaviour. That spiritual whole leaves nothing outside itself, and cannot be identified with what is interpreted as mere individual existence with its here and now.

Like the Copernican discovery, and to a less extent other great scientific discoveries, the Darwinian discovery of organic evolution has to a certain extent disturbed the balance of philosophical reasoning, in addition to acting as a great stimulus to that reasoning. It has thus to some extent tended to throw us back towards pre-Kantian philosophical ideas. One of these ideas is that the spiritual world of conscious behaviour has arisen out of something that is not itself. In actual fact what is taken for a non-spiritual world is only part of the spiritual world of conscious behaviour.

The holism of mere life, or the more dimly apprehended holism of the inorganic world, as it is appearing in the new physics, is different from the spiritual holism of conscious behaviour, since the latter kind of holism includes time-relations as well as space-relations. Just as we cannot coherently conceive life as dependent on, or arising out of, mechanism, so we cannot conceive conscious behaviour as dependent on, or arising out of, mere life. It has become customary in recent times to use such expressions as “unconscious mind” or “the unconscious” in the sense of something which originates conscious behaviour. So, before Pasteur, and to a still greater extent before Redi, men regarded living organisms as arising out of lifeless material, and attributed infection to such things as sewer-gas.

We have only to consider what life implies, and what a simple gas or liquid is ordinarily regarded as being, in order to realize that the immediate generation of life from the gas or liquid does not represent any coherent idea. Similarly, the generation of conscious behaviour out of something which is regarded as not having the specific characters of conscious behaviour is not a coherent conception. It only serves to shelve what is still left as an unsolved problem, just as the mechanistic conception of conscious behaviour shelves the problem of how a Newtonian universe can be related to a mind perceiving and acting on it. The problem left unsolved is a very real and pressing one, as will be pointed out more fully in the last lecture of this series.

For the present I must conclude this discussion by once more emphasizing the distinction between mere life and conscious behaviour. In the second series of lectures I hope to return to the discussion in its wider philosophical relations.