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Brown Thomas
Lectures on the Philosophy of the Human Mind (Vol. 1 of 3)

“I apprehend,” says Dr Reid, “that, besides the sensations, that are either agreeable or disagreeable, there is still a greater number that are indifferent. To these we give so little attention, that they have no name, and are immediately forgot, as if they had never been; and it requires attention to the operations of our minds, to be convinced of their existence. For this end, we may observe, that, to a good ear, every human voice is distinguishable from all others. Some voices are pleasant, some disagreeable; but the far greater part can neither be said to be one or the other. The same thing may be said of other sounds, and no less of tastes, smells, and colours; and if we consider, that our senses are in continual exercise while we are awake, that some sensation attends every object they present to us, and that familiar objects seldom raise any emotion, pleasant or painful, – we shall see reason, besides the agreeable and disagreeable, to admit a third class of sensations, that may be called indifferent. The sensations that are indifferent, are far from being useless. They serve as signs, to distinguish things that differ; and the information we have concerning things external, comes by their means. Thus, if a man had no ear to receive pleasure from the harmony or melody of sounds, he would still find the sense of hearing of great utility; though sounds gave him neither pleasure nor pain, of themselves, they would give him much useful information; and the like may be said of the sensations we have by all the other senses.”⁶⁶

It is as signs, indeed, far more than as mere pleasures in themselves, that our sensations are to us of such inestimable value. Even in the case to which I before alluded, of the symbolic or arbitrary characters of a language, when we consider all the important purposes to which these are subservient, as raising us originally from absolute barbarism, and saving us from relapsing into it, there might be an appearance of paradox, indeed, but there would be perfect truth in asserting, that the sensations which are themselves indifferent, are more precious, even in relation to happiness itself, than the sensations which are themselves accompanied with lively delight, or rather, of which it is the very essence to be delightful. Happiness, though necessarily involving present pleasure, is the direct or indirect, and often the very distant result of feelings of every kind, pleasurable, painful, and indifferent. It is like the beautiful profusion of flowers, which adorn our summer fields. In our admiration of the foliage, and the blossoms, and the pure airs and sunshine, in which they seem to live, we almost forget the darkness of the soil in which their roots are spread. Yet how much should we err, if we were to consider them as deriving their chief nutriment from the beams that shine around them, in the warmth and light of which we have wandered with joy. That delightful radiance alone would have been of little efficacy, without the showers, from which, in those very wanderings, we have often sought shelter at noon; or at least without the dews, which were unheeded by us, as they fell silently and almost insensibly on our evening walk.

With the common division of our sensations into five classes, – those of smell, taste, hearing, sight, touch, we have been familiar, almost from our childhood; and though the classification may be far from perfect, in reference to our sensations themselves, considered simply as affections of the mind, it is sufficiently accurate, in reference to the mere organs of sense; for, though our sensations of heat and cold, in one very important respect, which is afterwards to be considered by us, have much less resemblance to the other sensations which we acquire by our organs of touch, or at least to sensations, which we are generally supposed to derive from that organ, than to sensations, which we receive by the medium of other organs, our sensations of smell and sound for example – still, as they arise from an affection of the same organ, they may be more conveniently referred to the same, than to any other class; since, if we quit that obvious line of distinction, which the difference of organs affords, we shall not find it easy to define them by other lines as precise.

But whatever may be the arbitrary division or arrangement which we may form either of our sensations themselves, or of the organs that are previously affected, the susceptibility of the mind, by which it is capable of being affected by the changes of state in our mere bodily organs, must be regarded as, in every sense of the word, of primary value in our mental constitution. To the individual, indeed, it may be said to be in itself all the things which are around him, however near or afar; because it is truly that, by which alone all things near or afar become known to him. It constitutes by this mutual relation, which it establishes, a power of more than magic agency, before which the great gulf, that appeared to separate forever the worlds of matter and of spirit, disappears, – which thus links together substances, that seemed, in their nature, incapable of any common bond of union, – and which, bringing the whole infinity of things, within the sphere of our own mind, communicates to it some faint semblance of the omnipresence of its Author. “What is that organ,” – says an eloquent French writer, speaking of the eye, – “what is that astonishing organ, in which all objects acquire, by turns, a successive existence, – where the spaces, the figures, and the motions, that surround me, are as it were created, – where the stars, that exist at the distance of a hundred millions of leagues, become a part of myself, – and where in a single half inch of diameter, is contained the universe?” This power of external sense, which first awakes us into life, continues, ever after, to watch, as it were, round the life which it awoke, lavishing on us perpetual varieties of instruction and delight; and if, from the simple pleasures, and simple elementary knowledge which it immediately affords, we trace its influence, through all the successive feelings to which it indirectly gives rise, it may be said to exist, by a sort of intellectual and moral transmutation, in the most refined and etherial of all our thoughts and emotions. What Grey says of it, – in the commencement of his beautiful fragment De Principiis Cogitandi, addressed to his friend West, is not too high a panegyric, – that every thing delightful and amiable, friendship and fancy, and wisdom itself, have their primary source in it.

 
“Non illa leves primordia motus
Quanquam parva, dabunt. Lætum vel amabile quicquid
Usquam oritur, trahit hinc ortum; nec surgit ad auras,
Quin ea conspirent simul, eventusque secundent.
Hinc variæ vitai artes, ac mollior usus,
Dulce et amicitiæ vinclum: Sapientia dia
Hinc roseum accendit lumen, vultuque sereno,
Humanas aperit mentes, nova gaudia monstrans.
Illa etiam, quæ te (mirum) noctesque diesque
Assidue fovit inspirans, linguamque sequentem
Temperat in numeros, atque horas mulcet inertes,
Aurea non alia si jactat origine Musa.”⁶⁷
 

So much, indeed, of human knowledge, and of all that is valuable and delightful in human feeling, involves these elementary sensations, as it were in the very essence of the thoughts and feelings themselves, that one of the most acute of modern French metaphysicians, and, with scarcely an exception, all the philosophers of the French metaphysical school, who are his followers, have considered the whole variety of human consciousness, as mere sensation variously transformed; though, in stating the nature of this transformation, and the difference of the sensations as transformed from the primary forms of mere external feeling, they have not been so explicit, as the assertors of a system so paradoxical ought assuredly to have been. On the fallacies of this very prevalent theory of mind, however, which is afterwards to be examined by us fully, I need not at present make any remarks.

Though this excessive simplification of the phenomena of human thought and feeling is, however, far more than the phenomena truly allow, it is not the less certain, that all the varieties of our consciousness, though not mere transformations of external sense, are, when traced to their source, the results of sensation, in its various original forms. In inquiring into the phenomena of our senses, then, we begin our inquiry, where knowledge itself begins, and though the twilight, which hangs over this first opening of intellectual life, is perhaps only a presage, or a part of that obscurity which is to attend the whole track of human investigation, it still is twilight only, not absolute darkness. We can discover much, though we cannot discover all; and where absolute discovery is not allowed, there is still left to us a probability of conjecture, of which, in such limited circumstances, even philosophy may justly avail herself, without departing from her legitimate province.

LECTURE XIX
BRIEF NOTICE OF THE CORPOREAL PART OF THE PROCESS, IN SENSATION

The mental phenomena, of the class which is at present under our consideration, being those, which arise, in consequence of certain previous affections of our organs of sense, it is necessary, that we should take some notice of the corporeal part of the process; though it must always be remembered, that it is the last part of the process, the mental affection only, which truly belongs to our science, – and that, if this, in all its varieties, had been the result of any other species of affections of organs constituted in any other manner, – as long as there was the regular correspondence of certain mental affections with certain organic affections, – the philosophy of mind would have continued precisely the same as now. Our systems of anatomy, and of the physiology of our mere bodily frame, would indeed have been different, – but not that more intimate physiology, which relates to the functions of the animating spirit, whose presence is life, and without which our bodily frame, in all its beautiful adaptation of parts to parts, is a machine, as inert and powerless, as the separate atoms that compose it.

The great essential organ of all sensation is the brain, with its appendages, particularly the nerves that issue from it to certain organs, which are more strictly termed the organs of sense; as it is there the immediate objects, or external causes of sensation, the particles of light, for example, in vision, or of odour in smell, arrive, and come, as it were, into contact with the sensorial substance. Each organ, as you well know, has objects peculiar to itself, which it would be superfluous to enumerate; and since the blind are still sensible of sound, the deaf of colour, and both of smell, and taste, and touch, there must evidently be some difference, either in the sensorial substance itself which is diffused over the different organs, or in the mode of its diffusion and exposure in the different organs, from which this striking diversity of their relative sensibilities proceeds. The nervous matter however, considered separately from the coats in which it is enveloped, is of the same half-fibrous, but soft and pulpy texture, as the substance of the brain itself, and is in perfect continuity with that substance, forming, therefore, with it, what may be considered as one mass, as much as the whole brain itself may be considered as one mass; which has, indeed, for its chief seat the great cavity of the head; the

 
“Superas hominis sedes, arcemque cerebri;
Namque illic posuit solium, et sua templa sacravit,
Mens animi; – ”⁶⁸
 

but which extends, by innumerable ramifications, over the whole surface, and through the internal parts of the body. The mind, in that central brain in which it is supposed to reside, communicating with all these extreme branches, has been compared, by a very obvious, but a very beautiful similitude, to the parent Ocean, receiving from innumerable distances the waters of its filial streams:

 
“Ac uti longinquis descendunt montibus amnes,
Velivolus Tamisis, flaventisque Indus arenæ,
Euphratesque, Tagusque, et opimo flumine Ganges,
Undas quisque suas volvens, – cursuque sonoro
In mare prorumpunt; hos magno acclinis in antro
Excipit Oceanus, natorumque ordine longo
Dona recognoscit venientum, ultroque serenat
Coeruleam faciem, et diffuso marmore ridet.
Haud aliter species properant se inferre novellæ
Certatim menti.”⁶⁹
 

In the brain itself, the anatomist is able to shew us, with perfect clearness, many complicated parts, which we must believe to be adapted for answering particular purposes in the economy of life; but when we have gazed with admiration on all the wonders which his dissecting hand has revealed to us, and have listened to the names with which he most accurately distinguishes the little cavities or protuberances which his knife has thus laid open to our view, we are still as ignorant as before of the particular purposes to which such varieties of form are subservient; and our only consolation is, – for there is surely some comfort in being only as ignorant as the most learned, – that we know as much of the distinct uses of the parts as the anatomist himself, who exhibits them to us, and teaches us how to name them. A structure, in every respect different, though assuredly less fit than the present which has been chosen by infinite wisdom, might, as far as we know, have answered exactly the same end; which is as much as to say, that our ignorance on the subject is complete. The only physiological facts of importance, in reference to sensation, are, that if the nerves, which terminate in particular organs, be greatly diseased, the sensations which we ascribe to those particular organs cease; and cease, in like manner, if the continuity of the nerves be destroyed, by cutting them in any part of their course, or if, without loss of absolute continuity, their structure, in any part of their course be impaired by pressure, whether from tight ligatures drawn around them for the purpose of experiment, or from natural morbid causes. In short, if the brain and nerves be in a sound state, and certain substances be applied to certain parts of the nervous system, – as, for instance, sapid bodies to the extremities of the nerves of taste, or light to that expansion of the optic nerve, which forms what is termed the retina, – there is then instant sensation; and when the brain itself is not in a sound state to a certain extent, or when the nerve which is diffused on a particular organ is, either at this extremity of it, or in any part of its course, to a certain degree impaired, then there is no sensation, though the same external causes be applied. This very slight general knowledge of the circumstances in which sensation takes place, and of the circumstances in which it does NOT take place, is all the knowledge which physiology affords us of the corporeal part of the process; – and it is likely to continue so forever, – at least in all the more important respects of our ignorance, – since any changes which occur in the corpuscular motion, and consequent new arrangement of the particles of the substance of the brain and nerves, corresponding with the diversities of feeling during those particular states, – if such corpuscular motions or changes do really take place, – are probably far too minute to be observable by our organs; even though we could lay open all the internal parts of the brain to complete observation, without destroying, or at all affecting, the usual phenomena of life: —

 
In “following life through creatures we dissect,
We loose it, in the moment we detect.”
 

Indeed, we are not able to do even so much as this; for life has already vanished, long before we have come upon the verge of its secret precincts. It is like a Magician, that operates at a distance on every side, but still keeps himself apart, within a narrow circle. If we remain without the circle, we may gaze with never-ceasing admiration, on the wonders that play in rapid succession before our eyes. But, if we rush within, to force an avowal, of the secret energy that produces them, the enchanter and the enchantments alike are fled.

The brain, then, and the various nerves of sense in continuity with it, may, when taken together, be considered as forming one great organ, which I would term briefly the sensorial organ, essential to life, and to the immediate production of those mental phenomena which constitute our sensations, and, perhaps, too, modifying in some measure, directly or indirectly, all the other phenomena of the mind.

 
“Dum mens alma caput cerebrique palatia celsa
Occupat, et famulos sublimis dirigit artus,
Et facili imperio nervorum flectit habenas,
Illius ad nutum sensus extranea rerum
Explorant signa, et studio exemplaria fido
Ad dominam adducunt; vel qui statione locantur
Vicina, capitisque tuentur limina, ocelli,
Naresque, auriculæque, et vis arguta palati;
Vel qui per totam currit sparso agmine molem
Tactus, ad extremas speculator corporis aras.
His sensim auxiliis instructa fidelibus, olim
Mens humilis nulloque jacens ingloria cultu
Carceris in tenebris mox sese attolit in auras
Dives opum variarum, et sidera scandit Olympi.”
 

Of the nature of the connexion of this great sensorial organ with the sentient mind, we never shall be able to understand more than is involved in the simple fact, that a certain affection of the nervous system precedes immediately a certain affection of the mind. But, though we are accustomed to regard this species of mutual succession of bodily and mental changes, as peculiarly inexplicable, from the very different nature of the substances which are reciprocally affected, it is truly not more so than any other case of succession of events, where the phenomena occur in substances that are not different in their properties, but analogous, or even absolutely similar; since, in no one instance of this kind, can we perceive more than the uniform order of the succession itself; and of changes, the successions of which are all absolutely inexplicable, or, in other words, absolutely simple, and unsusceptible, therefore, of further analysis, none can be justly said to be more or less so than another. That a peculiar state of the mere particles of the brain, should be followed by a change of state of the sentient mind, is truly wonderful; but if we consider it strictly, we shall find it to be by no means more wonderful, than that the arrival of the moon, at a certain point of the heavens, should render the state of a body on the surface of our earth, different from what it otherwise would naturally be or that the state of every particle of our globe, in its relative tendencies of gravitation, should be instantly changed, as it unquestionably would be, by the destruction of the most distant satellite of the most distant planet of our system, or probably too, by the destruction even of one of those remotest of stars, which are illuminating their own system of planets, so far in the depth of infinity, that their light, – to borrow a well-known illustration of sidereal distance, – may never yet have reached our earth, since the moment at which they darted forth their first beams, in the creation of the universe. We believe, indeed, with as much confidence, that one event will uniformly have for its consequent another event, which we have observed to follow it, as we believe the simple fact that it has preceded it, in the particular case observed. But the knowledge of the present sequence, as a mere fact, to be remembered, and the expectation of future similar sequences, as the result of an original law of our belief, are precisely of the same kind, whether the sequence of changes be in mind, or in matter singly, or reciprocally in both.

What the nature of the change is, that is produced at the extremity of the nerve, it is beyond our power to state, or even to guess; and we are equally ignorant of the manner in which this affection of the nerve is communicated, or is supposed to be communicated, to the brain. But that some affection is gradually propagated, from the one to the other, so as to render the change in the state of the brain subsequent, by a certain interval, to the change in the state of the nerve, is universally believed. In applying to this change the term impression, a term indeed which had been in common use before, Dr Reid is careful to point out the reason for which this term appears to him preferable to others; and though I confess that the word seems to me to convey too much the notion of a peculiar well known species of action; that which consists in producing a certain configuration of the object impressed, corresponding with the figure of the impressing object, the very notion that has had so pernicious an effect in the theory of perception; and though I conceive the simple term change or affection to be all which is safely admissible, as long as the nature of the particular change is absolutely unknown; still it must be confessed that impression is a term a little more general than the other names of action, to which Dr Reid alludes, and therefore preferable to them, in the present case.

“There is sufficient reason,” he says, “to conclude, that, in perception, the object produces some change in the organ; that the organ produces some change upon the nerve; and that the nerve produces some change in the brain. And we give the name of an impression to those changes, because we have not a name more proper to express, in a general manner, any change produced in a body, by an external cause, without specifying the nature of that change. Whether it be pressure, or attraction, or repulsion, or vibration, or something unknown, for which we have no name, still it may be called an impression. But with regard to the particular kind of this change or impression, philosophers have never been able to discover any thing at all.”⁷⁰

That the word impression is not so free, as Dr Reid supposes, from that hypothetical meaning which he wished to avoid, I have already remarked. But the reason assigned by him for his preference of it, is unquestionably a just one; since a phrase which expresses the least possible knowledge, must be allowed to be the best suited to human ignorance, – that ignorance, which, not in the philosophy of intellect only, but in whatever track of science we may proceed, and whatever truths we may proudly discover in our way, still meets us at the end of every path, as if to mock at once our weakness and our pride, – and which seems to us to be every where, because it is, wherever we are ourselves. The splendour of nature, as it exists in itself, is, if I may speak figuratively, like sunshine on a boundless plain, on the flowers and herbage of which, though there be innumerable varieties of colour, there is brilliancy in all. But the misfortune is, that, as soon as we have approached near enough to distinguish the diversity of tints, their brilliancy is so obscured by our very approach to them, that their nice diversities are no longer distinguishable; as if man could not move along, without throwing his own shadow on every thing before him.

When I say, that we are ignorant of the nature of that change, which is propagated along the nerve to the brain, I speak in reference to an opinion that is universal. But, though it may be improbable, it is certainly far from impossible, that there is really no such progressive communication, as this which is supposed. The brain and nerves, though, from the difference of names, you might be led, perhaps, to consider them as distinct, I have already said, are not separate organs, but are in continuity with each other, at least as much as various parts of the brain itself, which are comprehended under that single term, can be said to be continuous. When taken together, they form what is truly one complicated sensorial organ, – the organ of all our sensations, according to the different states in which the organ exists, or the different parts of it which are chiefly affected. In hearing, for example, a certain state of that part of the sensorial organ, which constitutes the auditory nerves, – in vision, a certain state of that part of it, which constitutes the optic nerves, is necessary to sensation, – and, in both cases, according to the universal supposition on the subject, all or part of the brain likewise must exist in a certain state, of which we know nothing more, than that it is followed, in the one case, by the sensation of sound, in the other case by that of sight. The connexion of the mind with the bodily frame, – which must be equally inexplicable on every supposition that can be formed, – is not supposed, by any philosopher, to depend on the state of a single physical point of the brain alone; and, if it extend to more than one such point, there is nothing, – in the nature of the connexion itself, independently of experience, – which necessarily limits it to one portion of the complex sensorial organ, more than to another, – to the particles of the central mass of the brain, for example, more than to those of the nerve itself. It is experience, then, to which we are referred; and experience, though it shows that certain nerves are not essential to life, since life continues equally, after they may have been impaired, or even destroyed, is far from showing that an affection of them is not essential to sensation, at the very moment of the particular sensation; nor does it afford even the slightest evidence, to justify the belief, that the only use of the nerve is to communicate a certain affection to the brain, which affection of the mere central part of the sensorial organ, would, of itself, immediately induce sensation, though the nerves were annihilated in the preceding instant. The sensation may be the immediate effect, not of the state of the brain only, but of the state of the brain, and of any particular nerve, considered as existing together at the moment; in the same manner, as, by those who ascribe the immediate origin of sensation to the mere brain, exclusive of its nervous appendages, it is supposed to depend on the state, not of one physical point of the central brain, but on the state of many such co-existing points. We know not, to what extent, in the great sensorial organ, this change is necessary; but we believe, that, to some extent, it is necessary; and the question is, whether, in the whole portion so affected, the affection be produced by a succession of changes, propagated from part to part? This may, perhaps, be the more probable supposition: – but, whatever may be the comparative probability or improbability, it certainly has not been demonstrated by observation or experiment; nor can there be said to be, a priori, any absurdity in the opposite supposition, that the sensorial affection, to whatever extent it may be necessary, is not progressive, but immediate, – that, as long as the sensorial organ, (under which term I comprehend, as I have already frequently repeated, not the brain merely, but also its nervous appendages, that exist in apparent continuity with the brain,) is unimpaired, by accident or disease, the presence of the immediate object of sense, at the external organ, which on every supposition, must be followed by some sensorial change of state, is instantly followed by that general change of state of the internal organ, whatever it may be, which is necessary to sensation, in the particular case; in the same manner, as the presence of a celestial body, at a certain point in the heavens, is immediately followed by a change of state, in the whole gravitating particles of our globe; the change in any long line of these gravitating particles being not communicated from each to each, but depending only on the presence of the distant sun or planet; and beginning in the most remote particles of the line, at the very same instant, as in that which is nearest, on the surface of the earth. An instant change, in the long line of sensorial particles, – if the affection of a long line of these particles be necessary, – on the presence of a particular object, is not more improbable in itself, than this instant and universal influence of gravitation, that varies with all the varying positions of a distant object.

But is it, indeed, certain, that, in sensation, there is an affection of the central brain, whether immediate or progressive? Is it not possible, at least, or more than possible, that the state of the mind, when we perceive colours and sounds, may be the immediate consequent of the altered state of that part of the sensorial organ, which forms the expansion of the nerve in the eye or ear? The sensations must be supposed, in every theory, to be the consequents of states induced in some sensorial particles, and there is nothing but the mere names of brain and nerve, invented by ourselves, and the notions which we have chosen, without evidence, to attach to these mere names, which would mark the sensorial particles in the nervous expanse itself, as less fitted to be the immediate antecedents of sight and hearing, than the similar sensorial particles in any portion of the central mass of the brain. There is no reason, in short a priori, for supposing that a state of the sensorial particles of the nerves cannot be the cause of sensation, and that the sensation must be the effect of a state equally unknown, of apparently similar particles, in that other part of the general sensorial organ, which we have denominated the brain. Sensation, indeed, is prevented by decay, or general disease of the brain, or by separation of the nerve, or pressure on it, in any part of its course. But it is far from improbable, that these causes, which must evidently be injurious to the organ, may act, merely by preventing that sound state of the nerve, which is necessary for sensation, and which, in an organ so very delicate, may be affected by the slightest influences, – by influences far slighter, than may naturally be expected to result from such an injury of such a part. The nerves and brain, together, form one great organ; and a sound state of the whole organ, even from the analogy of other grosser organs, may well be supposed to be necessary for the healthy state and perfect function of each separate part.