Chapter XVII: Part 17

To those who are wholly unacquainted with the theory of vision, nothing certainly can seem, as first stated, more absurd than the assertion, that we see, not with our eyes merely, but chiefly by the medium of another organ, which the blind possess in as great perfection as ourselves, and which, at the moment of vision, may perhaps be absolutely at rest. It must not surprise you, therefore, though the element which seems to me to form the most important constituent of our notion of extension should in like manner, as first stated to you, seem a very unlikely one.

This element is our feeling of _succession_, or time--a feeling, which necessarily, involves the notion of divisibility or series of parts, that is so essential a constituent of our more complex notion of matter,--and to which notion of continuous divisibility, if the notion of resistance be added, it is scarcely possible for us to imagine, that we should not have acquired, by this union, the very notion of physical extension,--that which has parts, and that which resists our effort to grasp it.

That _memory_ is a part of our mental constitution, and that we are thus capable of thinking of a series of feelings, as successive to each other, the experience of every moment teaches us sufficiently. This succession frequently repeated, suggests immediately, or implies the notion of length, not metaphorically, as is commonly said, but as absolutely as extension itself: and, the greater the number of the successive feelings may have been, the greater does this length appear. It is not possible for us to look back on the years of our life, since they form truly a progressive series, without regarding them as a sort of length, which is more distinct indeed, the nearer the succession of feelings may be to the moment at which we consider them, but which, however remote, is still felt by us as _one continued length_, in the same manner, as when, after a journey of many hundred miles, we look back, in our memory, on the distance over which we have passed, we see, as it were, a long track of which some parts, particularly the nearer parts, are sufficiently distinct, but of which the rest seems lost in a sort of distant obscurity. The line of our long journeying--or, in other words, that almost immeasurable line of plains, hills, declivities, marshes, bridges, woods,--to endeavour to comprehend which in our thought, seems an effort as fatiguing as the very journey itself--we know well, can be divided into those various parts:--and, in like manner, the progressive line of time--or, in other words, the continued succession, of which the joy, the hope, the fragrance, the regret, the melody, the fear, and innumerable other affections of the mind, were parts, we feel that we can mentally divide into those separate portions of the train. Continuous length and divisibility, those great elementary notions of space, and of all that space contains, are thus found in every succession of our feelings. There is no language in which time is not described as long or short,--not from any metaphor--for no mere arbitrary metaphor can be thus universal, and inevitable, as a form of human thought--but because it is truly impossible for us to consider succession, without this notion of progressive divisibility attached to it: and it appears to us as absurd to suppose, that by adding, to our retrospect of a week, the events of the month preceding, we do not truly lengthen the succession, as it would be to suppose, that we do not lengthen the line of actual distance, by adding, to the few last stages of a long journey, the many stages that preceded it.

It is this spreading out of life into a long expanse, which allows man to create, as it were, his own world. He cannot change, indeed, the scene of external things. But this may be said, in one sense, to be the residence only of his corporeal part. It is the moral scene in which the spirit truly dwells; and this adapts itself, with harmonious loveliness, or with horror as suitable, to the character of its pure or guilty inhabitant. If but a single moment of life,--a physical _point_, as it were, of the long line--could be reviewed at once, conscience would have little power of retribution. But he who has lived, as man should live, is permitted to enjoy that best happiness which man can enjoy,--to behold, in one continued series, those years of benevolent wishes or of heroic suffering, which are at once his merit and his reward. He is surrounded by his own pure thoughts and actions, which, from the most remote distance, seem to shine upon him wherever his glance can reach; as in some climate of perpetual summer, in which the inhabitant sees nothing but fruits and blossoms, and inhales only fragrance, and sunshine, and delight. It is in a moral climate as serene and cloudless, that the destined inhabitant of a still nobler world moves on, in that glorious track, which has heaven before, and virtue and tranquillity behind;--and in which it is scarcely possible to distinguish, in the immortal career, when the earthly part has ceased, and the heavenly begins.

Is it in _metaphor_ only, that a youth and maturity, and old age of guilt, seem to stretch themselves out in almost endless extent, to that eye which, with all its shuddering reluctance, is still condemned to gaze on them,--when, after the long retrospect seems finished, some fraud, or excess, or oppression, still rises and adds to the dreadful line--and when eternity itself, in all the horrors which it presents, seems only a still longer line of the same dreadful species, that admits of no other measure, than the continued sufferings, and remembrance, and terrors that compose it!

It is a just and beautiful observation of an ancient Stoic, that _time_ which is _past_ is like something consecrated to the gods, over which fortune and mortality have no longer any power, and that, dreadful as it must be to the wicked, to whom their own memory is an object of terror, it still, to the virtuous, offers itself as a consolation or joy--not in single moments like the present hour, but in all that long series of years which rises before us, and remains with us at our bidding. “Ille qui multa ambitiosè cupiit, superbè contempsit, insidiosè decepit, avarè rapuit, prodigè effudit,--necesse est memoriam suam timeat. Atqui hæc est pars temporis nostri sacra ac dedicata, omnes humanos casus supergressa, extra regnum fortunæ subducta; quam non inopia, non metus, non morborum incursus exagitat. Hæc nec turbari nec eripi potest; perpetua ejus et intrepida possessio est. Singuli tantùm dies, et hi per momenta, præsentis sunt: at præteriti temporis omnes, cum jusseris aderunt, ad arbitrium tuum se inspici ac detineri patientur.”

By those, who can look back on years that are long past, and yet say, that the continued progress, or the length and the shortness of time, are only _metaphorical_ expressions, it might be said with equal justness, that the roundness of a sphere, is a metaphor, or the angularity of a cube. We do not more truly consider the one as angular and the other as round, than we consider the time to be continuously progressive, in which we considered, first the one figure, and then the other, and inquired into the properties of each. That which is progressive must have _parts_. Time, or succession, then involves the very notions of longitudinal extension and divisibility, and involves these, without the notion of any thing external to the mind itself;--for though the mind of man had been susceptible only of joy, grief, fear, hope, and the other varieties of internal feeling, _without_ the possibility of being affected by external things, he would still have been capable of considering these feelings, as successive to each other, in a long continued progression, divisible into separate parts. The notions of length, then, and of divisibility, are not confined to external things, but are involved, in that very memory, by which we consider the series of the past,--not in the memory of distant events only, but in those first successions of feeling, by which the mind originally became conscious of its own permanence and identity. The notion of time, then, is precisely coeval with that of the mind itself; since it is implied in the knowledge of succession, by which alone, in the manner formerly explained to you, the mind acquires the knowledge of its own reality, as something more than the mere sensation of the present moment.

Conceiving the notion of time, therefore, that is to say of feelings past and present, to be thus one of the earliest notions which the infant mind can form, so as to precede its notions of external things, and to involve the notions of length and divisibility, I am inclined to reverse exactly the process commonly supposed; and, instead of deriving the measure of time from extension, to derive the knowledge and original measure of extension from time. That one notion or feeling of the mind may be united indissolubly with other feelings, with which it has frequently coexisted, and to which, but for this coexistence, it would seem to have no common relation, is sufficiently shown by those phenomena of vision to which I have already so frequently alluded.

In what manner, however, is the notion of time peculiarly associated with the simple sensation of touch, so as to form, with it, the perception of extension? We are able, in the theory of vision, to point out the coexistence of sensations which produce the subsequent union; that renders the perception of distance apparently immediate. If a similar coexistence of the original sensations of touch, with the notion of continued and divisible succession, cannot be pointed out in the present case, the opinion which asserts it, must be considered merely as a wild and extravagant conjecture.

The source of such a coexistence is not merely to be found, but is at least as obvious, as that which is universally admitted in the case of vision.

Before I proceed, however, to state to you, in what way I conceive the notion to be acquired, I must again warn you of the necessity of banishing, as much as possible, from your view of the mind of the infant in this early process, all those notions of external things, which we are so apt to regard as almost original in the mind, because we do not remember the time, when they arose in our own. As we know well, that there are external things, of a certain form, acting on our organs, which are also of a certain form, it seems so very simple a process, to perceive extension--that is to say, to know that there exist without us those external forms, which really exist--that to endeavour to discover the mode, in which extension, that now appears so obvious a quality of external things, is perceived by us, seems to be a needless search, at a distance, for what is already before our very eyes. And it will be allowed, that all this would, indeed, be very easy to a mind like ours, after the acquisitions of knowledge which it has made; but the difficulty of the very question is, how the mind of the infant makes these acquisitions, so as to become like ours. You must not think of a mind, that has any knowledge of things external, even of its own bodily organs, but of a mind simply affected with certain feelings, and having nothing but these feelings to lead it to the knowledge of things without.

To proceed, then,--The hand is the great organ of touch. It is composed of various articulations, that are easily moveable, so as to adapt it readily to changes of shape, in accommodation to the shape of the bodies which it grasps. If we shut our hand gradually, or open it gradually, we find a certain series of feelings, varying with each degree of the opening or closing, and giving the notion of succession of a certain length. In like manner, if we gradually extend our arms, in various directions, or bring them nearer to us again, we find that each degree of the motion is accompanied with a feeling that is distinct, so as to render us completely conscious of the progression. The gradual closing of the hand, therefore, must necessarily give a succession of feelings,--a succession, which, of itself, might, or rather must, furnish the notion of length, in the manner before stated, the length being different, according to the degree of the closing; and the gradual stretching out of the arm gives a succession of feelings, which, in like manner, must furnish the notion of length,--the length being different according to the degree of the stretching of the arm. To those who have had opportunities of observing infants, I need not say, how much use, or rather what constant use, the future inquirer makes of his little fingers and arms; by the frequent contraction of which, and the consequent renewal of the series of feelings involved in each gradual contraction, he cannot fail to become so well acquainted with the progress, as to distinguish each degree of contraction, and, at last, after innumerable repetitions, to associate with each degree the notion of a certain length of succession. The particular contraction, therefore, when thus often repeated, becomes the representative of a certain length, in the same manner as shades of colour, in vision become ultimately representative of distance,--the same principle of association, which forms the combination in the one case, operating equally in the other.

In these circumstances of acquired knowledge,--after the series of muscular feelings, in the voluntary closing of the hand, has become so familiar, that the whole series is anticipated and expected, as soon as the motion has begun,--when a ball, or any other substance, is placed for the first time in the infant's hand, he feels that he can no longer perform the usual contraction,--or, in other words, since he does not fancy that he has muscles which are contracted, he feels that the usual series of sensations does not follow his will to renew it,--he knows how much of the accustomed succession is still remaining; and the notion of this particular length, which was expected, and interrupted by a new sensation, is thus associated with the particular tactual feeling excited by the pressure of the ball,--the greater or less magnitude of the ball preventing a greater or less portion of the series of feelings in the accustomed contraction. By the frequent repetition of this tactual feeling, as associated with that feeling, which attends a certain progress of contraction, the two feelings at last flow together, as in the acquired perceptions of vision; and when the process has been repeated with various bodies innumerable times, it becomes, at last, as impossible to separate the mere tactual feeling, from the feeling of length, as to separate the whiteness of a sphere, in vision, from that convexity of the sphere, which the eye, of itself, would have been forever incapable of perceiving.

As yet, however, the only dimension of the knowledge, of which we have traced the origin, is mere length; and it must still be explained, how we acquire the knowledge of the other dimensions. If we had had but one muscle, it seems to me very doubtful, whether it would have been possible for us, to have associated with touch any other notion than that of mere length. But nature has made provision, for giving us a wider knowledge, in the various muscles, which she has distributed over different parts, so as to enable us to perform motions in various directions at the same instant, and thus to have coexisting series of feelings, each of which series was before considered as involving the notion of length. The infant bends one finger gradually on the palm of his hand; the finger, thus brought down, touches one part of the surface of the palm, producing a certain affection of the organ of touch, and a consequent sensation; and he acquires the notion of a certain length, in the remembered succession of the muscular feelings during the contraction:--he bends another finger; it, too, touches a certain part of the surface of the palm, producing a certain feeling of touch, that coexists and combines, in like manner, with the remembrance of a certain succession of muscular feelings. When both fingers move together, the coexistence of the two series of successive feelings, with each of which the mind is familiar, gives the notion of coexisting lengths, which receive a sort of unity, from the proximity in succession of the tactual feelings in the contiguous parts of the palm which they touch,--feelings, which have before been found to be proximate, when the palm has been repeatedly pressed along a surface, and the tactual feelings of these parts, which the closing fingers touch at the same moment, were always immediately successive,--as immediately successive, as any of the muscular feelings in the series of contraction. When a body is placed in the infant's hand, and its little fingers are bent by it as before, sometimes one finger only is impeded in its progress, sometimes two, sometimes three,--and he thus adds to the notion of mere length, which would have been the same, whatever number of fingers had been impeded, the notion of a certain number of proximate and coexisting lengths, which is the very notion of breadth; and with these, according as the body is larger or smaller, is combined always the tactual affection produced by the pressure of the body, on more, or fewer, of the interior parts of the palm, and fingers, which had before become, of themselves, representative of certain lengths, in the manner described; and the concurrence of these three varieties of length, in the single feeling of resistance, in which they all seem to meet, when an incompressible body is placed within the sphere of the closing fingers,--however rude the notions of concurring dimensions may be, or rather must be, as at first formed,--seems at least to afford the rude elements, from which, by the frequent repetition of the feeling of resistance, together with the proximate lengths, of which it has become representative, clearer notions of the kind may gradually arise.

The progressive contractions of the various muscles which move the arms, as affording similar successions of feelings, may be considered in precisely the same light, as sources of the knowledge of extension; and, by their motion in various directions, at the same time with the motion of the fingers, they concur powerfully, in modifying, and correcting, the information received from these. The whole hand is brought, by the motion of the arm, to touch one part of the face or body; it is then moved, so as to touch another part, and, with the frequent succession of the simple feelings of touch, in these parts, is associated the feeling of the intervening _length_, derived from the sensations that accompanied the progressive contraction of the arm. But the motion is not always the same; and, as the same feeling of touch, in one part, is thus followed by various feelings of touch in different parts, with various series of muscular feelings between, the notion of length in various _directions_, that is to say, of length in various series commencing from one power, is obtained in another way. That the knowledge of extension, or in other words, the association of the notion of succession with the simple feelings of touch, will be rude and indistinct at first, I have already admitted; but it will gradually become more and more distinct and precise: as we can have no doubt, that the perception of distance by the eye, is, in the first stages of visual association, very indistinct, and becomes clearer after each repeated trial. For many weeks or months, all is confusion in the visual perceptions, as much as in the tactual and muscular. Indeed, we have abundant evidence of this continued progress of vision, even in mature life, when, in certain professions that require nice perceptions of distance, the power of perception itself, by the gradual acquisitions which it obtains from experience, seems to unfold itself more and more, in proportion to the wants that require it.

The theory of the notion of extension, of which I have now given you but a slight outline, might, if the short space of these Lectures allowed sufficient room, be developed with many illustrations, which it is now impossible to give to it. I must leave you, in some measure, to supply these for yourselves.

It may be thought, indeed, that the notion of _time_, or _succession_, is, in this instance, a superfluous incumbrance of the theory, and that the same advantage might be obtained, by supposing the muscular feelings themselves, independently of the notion of their succession, to be connected with the notion of particular lengths. But this opinion, it must be remarked, would leave the difficulty precisely as before; and sufficient evidence in confutation of it, may be found in a very simple experiment, which it is in the power of any one to make. The experiment I cannot but consider as of the more value, since it seems to me,--I will not say _decisive_, for that is too presumptuous a word,--but strongly _corroborative_ of the theory, which I have ventured to propose; for it shows, that, even after all the acquisitions, which our sense of touch has made, the notion of extension is still modified, in a manner the most striking and irresistible, by the mere change of accustomed _time_. Let any one, with his eyes shut, move his hand, with moderate velocity, along a part of a table, or any other hard smooth surface, the portion, over which he presses, will appear of a certain length; let him move his hand more rapidly, the portion of the surface pressed will appear _less_; let him move his hand _very slowly_, and the length, according to the degree of the slowness, will appear increased, in a most wonderful proportion. In this case, there is precisely the same quantity of muscular contraction, and the same quantity of the organ of touch compressed, whether the motion be rapid, moderate, or slow. The only circumstance of difference is the time, occupied in the succession of the feelings; and this difference is sufficient to give complete diversity to the notion of length.

If any one, with his eyes shut, suffer his hand to be guided by another, very slowly along any surface unknown to him, he will find it impossible to form any accurate guess as to its length. But it is not necessary, that we should be previously unacquainted with the extent of surface, along which the motion is performed; for the illusion will be nearly the same, and the experiment, of course, be still more striking, when the motion is along a surface with which we are perfectly familiar, as a book which we hold in our hand, or a desk at which we are accustomed to sit.

I must request you, not to take for granted the result which I have now stated, but to repeat for yourselves an experiment, which it is so very easy to make, and which, I cannot but think is so very important, as to the influence of _mere difference of time_, in our estimation of _longitudinal extent_. It is an experiment, tried, unquestionably, in most unfavourable circumstances, when our tactual feelings, representative of extension, are so strongly fixed, by the long experience of our life; and yet, even now, you will find, on moving your hand, slowly and rapidly, along the same extent of surface, though with precisely the same degree of pressure in both cases, that it is as difficult to conceive the extent, thus slowly and rapidly traversed, to be the same, as it is difficult to conceive the extent of visual distance to be exactly the same, when you look alternately through the different ends of an inverted telescope. If when all other circumstances are the same, the different visual feelings, arising from difference of the mere direction of light, be representative of length, in the one case,--the longer or shorter succession of time, when all other circumstances are the same, has surely as much reason to be considered as representative of it, in the other case.

Are we, then, to believe, that the _feeling_ of extension, or, in other words, of the definite figure of bodies, is a _simple feeling_ of touch, _immediate_, _original_, and _independent of time_; or is there not rather reason to think, as I have endeavoured to show, that it is a _compound_ feeling, of which _time_, that is to say, our notion of succession, is an _original element_?

LECTURE XXV.

ON THE DISTINCTION BETWEEN SENSATION AND PERCEPTION,--AND BETWEEN THE PRIMARY AND SECONDARY QUALITIES OF MATTER.

My last Lecture, Gentlemen, was chiefly employed in considering the nature of that complex process which takes place in the mind, when we ascribe the various classes of our sensations to their various external objects,--to the analysis of which process we were led, by the importance which Dr Reid has attached to the distinction of _sensation_ and _perception_;--a sensation, as understood by him, being the simple feeling that immediately follows the action of an external body on any of our organs of sense, considered merely as a feeling of the mind; the corresponding perception being a reference of this feeling to the external body as its cause.

The distinction I allowed to be a convenient one, if the nature of the complex process which it expresses be rightly understood. The only question that seemed, philosophically, of importance, with respect to it, was, whether the _perception_ in this sense,--the reference of the sensation to its external corporeal cause,--imply, as Dr Reid contends, a peculiar mental power, coextensive with sensation, to be distinguished by a peculiar name in the catalogue of our faculties, or be not merely one of the results of a more general power, which is afterwards to be considered by us,--the _power of association_,--by which one feeling suggests, or induces, other feelings that have formerly coexisted with it.

It would be needless to recapitulate the argument minutely, in its relation to _all_ the senses. That of smell, which Dr Reid has himself chosen as an example, will be sufficient for our retrospect.

Certain particles of odorous matter act on my nostrils,--a peculiar _sensation_ of fragrance arises,--I refer this sensation to a rose. This reference, which is unquestionably something superadded to the original sensation itself, is what Dr Reid terms the perception of the fragrant body. But what is the reference itself, and to what source is it to be ascribed? That we should have supposed our sensations to have had a cause of some sort, as we suppose a cause of all our feelings internal as well as external, may indeed be admitted. But if I had had no other sense than that of smell,--if I had never _seen_ a rose,--or, rather, since the knowledge which vision affords is chiefly of a secondary kind, if I had no mode of becoming acquainted with the compound of extension and resistance, which the mere sensations of smell, it is evident, are incapable of affording,--could I have made this reference of my sensation to a quality of a fragrant body? Could I, in short, have had more than the mere sensation itself, with that general belief of a cause of some sort, which is not confined to our sensations, but is common to them with all our other feelings?

By _mere smell_, as it appears to me, I could not have become acquainted with the existence of corporeal substances,--in the sense in which we now understand the term _corporeal_,--nor, consequently, with the _qualities_ of corporeal substances; and, if so, how could I have had that perception of which Dr Reid speaks,--that reference to a fragrant body, of which, as a body, I was before in absolute ignorance? I should, indeed, have ascribed the sensation to some cause or antecedent, like every other feeling; but I could as little have ascribed it to a bodily cause, as any feeling of joy or sorrow. I refer it now to a _rose_; because, being endowed with _other_ sensitive capacities, I have previously learned, from another source, the existence of causes without, extended and resisting,--because I have previously touched or seen a rose, when the sensation of fragrance coexisted with my visual or tactual sensation; and all which distinguishes the _perception_ from the mere _sensation_, is this suggestion of former experience, which reminds me now of other feelings, with the continuance or cessation of which, in innumerable former instances, the fragrance itself also continued or ceased. The perception in short, in smell, taste, hearing, is a sensation suggesting, by _association_, the notion of some extended and resisting substance, fragrant, vapid, vibratory,--a notion which smell alone, taste alone, hearing alone, never could have afforded; but which, when once received from any other source, may be suggested by these as readily as any other associate feeling that has frequently coexisted with them. To the simple primary sensations of _vision_ the same remark may be applied. A mere sensation of colour could not have made me acquainted with the existence of bodies, that would resist my effort to grasp them. It is only in one sense, therefore,--that which affords us the knowledge of _resistance_,--that any thing like original perception can be found; and even in this, the process of perception, as I formerly explained to you, implies no peculiar power, but only common sensations, with associations and inferences of precisely the same kind, as those which are continually taking place in all our reasonings and trains of thought.

_Extension_ and _resistance_, I need scarcely repeat, are the complex elements of what we term matter; and nothing is matter to our conception, or a body, to use the simpler synonymous term, which does not involve these elements. If we had no other sense than that of smell, and, therefore, could not have referred the sensations to any fragrant body, what, in Dr Reid's meaning of this term, would the supposed power of perception, in these circumstances, have been? What would it have been, in like manner, if we had had only the sense of taste in sweetness and bitterness,--or of hearing in melody,--or of vision in colour,--without the capacity of knowing light as a material substance, or the bodies that vibrated, or the bodies of another kind that were sweet or bitter? It is only by the sense of touch, or, at least, by that class of perceptions which Dr Reid ascribes to touch,--and which, therefore, though traced by us, in part, to another source, I, for brevity's sake, comprehend under that term in our present discussion,--it is only by _touch_ that we become acquainted with those elements which are essential to our very notion of a _body_; and to touch, therefore, in his own view of it, we must be indebted, directly or indirectly, as often as we refer the sensations of any other class to a _corporeal_ cause. Even in the supposed perceptions of touch itself, however, as we have seen, the reference of our feelings to an external cause is not demonstrative of any peculiar power of the mind, to be classed separately from its other faculties. But when a body is first grasped, in infancy, by fingers that have been accustomed to contract without being impeded, we learn to consider the sensation as the result of a cause that is different from our own mind, because it breaks an accustomed series of feelings, in which all the antecedents, felt by us at the time, were such as were before uniformly followed by a different consequent, and were expected, therefore, to have again their usual consequent. The _cause_ of the new sensation, which is thus believed to be something different from our sentient self, is regarded by us as something which has parts, and which resists our effort, that is to say, as an external body;--because the muscular feeling, excited by the object grasped is, in the _first_ place, the very feeling of that which we term resistance; and, _secondly_, because, by uniformly supplying the place of a definite portion of a progressive series of feelings, it becomes ultimately representative of that particular length of series, or number of parts, of which it thus uniformly supplies the place. Perception, then, even in that class of feelings by which we learn to consider ourselves as surrounded by substances extended and resisting, is only another name, as I have said, for the result of certain associations and inferences that flow from other more general principles of the mind; and with respect to all our other sensations, it is only another name for the suggestion of these very perceptions of touch, or at least of the feelings, tactual and muscular, which are, by Dr Reid, ascribed to that single sense. If we had been unsusceptible of these tactual and muscular feelings, and, consequently, had never conceived the existence of any thing extended and resisting till the sensation of fragrance, colour, sweetness, or sound had arisen, we should, after any one or all of these sensations, have still known as little of bodies without, as if no sensation whatever had been excited.

The distinction, then, on which Dr Reid has founded so much, involves, in his view of it, and in the view that is generally taken of it, a false conception of the nature of the process which he describes. The two words _sensation_ and _perception_, are, indeed, as I have already remarked, very convenient for expressing, in one case, the mere existence of an external feeling,--in the other case, the reference which the percipient mind has made of this feeling to an external cause. But this reference is all, which the perception superadds to the sensation;--and the source of the reference itself we are still left to seek, in the other principles of our intellectual nature. We have no need, however, to invent a peculiar power of the mind for producing it; since there are other principles of our nature, from which it may readily be supposed to flow,--the principle by which we are led to believe, that every new consequent, in a train of changes, must have had a new antecedent of some sort in the train,--and the principle of association, by which feelings, that have usually coexisted, suggest or become representative of each other. With these principles, it certainly is not wonderful, that when the fragrance of a rose has uniformly affected our sense of smell, as often as the flower itself was presented to us, we should ascribe the fragrance to the flower which we have seen and handled;--but though it would not be wonderful, that we should make it, it would indeed be wonderful, if, with these principles, we did not make that very reference, for which Dr Reid thinks it necessary to have recourse to a peculiar faculty of perception.

Such, then, is the view, which I would take of that distinction of _sensation_ and _perception_, which Dr Reid, and the philosophers who have followed him, and many of philosophers, too, that preceded him,--for the distinction, as I have said, is far from being an original one,--have understood in a different sense; in consequence, as I cannot but think, of a defective analysis of the mental process, which constitutes the reference of our feelings of this class to _causes_ that are _without_.

There is another distinction, which he has adopted from the philosophers that preceded him, and which forms an important part of his system of perception,--a distinction, that is just to a certain extent,--though not to the full extent, and in the precise manner, in which he and other writers have maintained;--and with respect to which, therefore, it will be necessary to point out to you, how far I conceive it to be safely admissible. I allude to the division, which has been formed of the _primary_ and _secondary_ qualities of matter.

“Every one knows that extension, divisibility, figure, motion, solidity, hardness, softness, and fluidity, were by Mr Locke called primary qualities of body; and that sound, colour, taste, smell, and heat or cold, were called secondary qualities. Is there a just foundation for this distinction? Is there any thing common to the primary, which belongs not to the secondary? And what is it?

“I answer, that there appears to me to be a real foundation for the distinction; and it is this: That our senses give us a direct and a distinct notion of the primary qualities, and inform us what they are in themselves; but of the secondary qualities, our senses give us only a relative and obscure notion. They inform us only, that they are qualities that affect us in a certain manner, that is, produce in us a certain sensation; but as to what they are in themselves, our senses leave us in the dark.

“The notion we have of primary qualities is direct, and not relative only. A relative notion of the thing, is, strictly speaking, no notion of the thing at all, but only of some relation which it bears to something else.

“Thus gravity sometimes signifies the tendency of bodies towards the earth; sometimes it signifies the cause of that tendency: When it means the first, I have a direct and distinct notion of gravity: I see it, and feel it, and know perfectly what it is; but this tendency must have a cause: We give the same name to the cause; and that cause has been an object of thought and of speculation. Now what notion have we of this cause, when we think and reason about it? It is evident, we think of it as an unknown cause, of a known effect. This is a relative notion, and it must be obscure; because it gives us no conception of what the thing is, but of what relation it bears to something else. Every relation which a thing unknown bears to something that is known, may give a relative notion of it; and there are many objects of thought, and of discourse, of which our faculties can give no better than a relative notion.

“Having premised these things to explain what is meant by a relative notion, it is evident, that our notion of primary qualities is not of this kind; we know what they are, and not barely what relation they bear to something else.

“It is otherwise with secondary qualities. If you ask me, what is that quality or modification in a rose which I call its smell, I am at a loss to answer directly. Upon reflection I find, that I have a distinct notion of the sensation which it produces in my mind. But there can be nothing like to this sensation in the rose, because it is insentient. The quality in the rose is something which occasions the sensations in me; but what that something is, I know not. My senses give me no information upon this point. The only notion, therefore, my senses give is this, That smell in the rose is an unknown quality or modification, which is the cause or occasion of a sensation which I know well. The relation which this unknown quality bears to the sensation with which nature hath connected it, is all I learn from the sense of smelling; but this is evidently a relative notion. The same reasoning will apply to every secondary quality.

“Thus I think it appears, that there is a real foundation for the distinction of primary from secondary qualities; and that they are distinguished by this, that of the primary we have by our senses a direct and distinct notion; but of the secondary only a relative notion, which must, because it is only relative, be obscure; they are conceived only as the unknown causes or occasions of certain sensations with which we are well acquainted.”[92]

Though, as I have explained to you fully, in my former Lectures, we should not,--at least in far the greater number of our sensations,--have considered them, originally, as proceeding from external causes, we yet, after the acquisitions of knowledge, with which the first years of our life enrich us, believe, that there is an external cause of all our sensations,--of smells and tastes, as much as of those feelings of the mind, which constitute our notions of extension and resistance. But the difference, in these cases, is, that though we _learn_, by experience of certain successions or co-existences of feelings, to refer to a _corporeal_ cause our sensations of fragrance, and various other species of sensations, there is nothing in the sensation of fragrance itself, or in the other analogous sensations, of which I speak, that might not indicate as much a cause directly spiritual, as a cause like that to which we at present give the name of _body_,--while the very notion of extension and resistance combined, seems necessarily to indicate a material cause, or rather is truly that which constitutes our very notion of matter.

We believe, indeed, that our sensations of fragrance, sweetness, sound, have causes of some sort, as truly as we believe, that our feelings of extension and resistance have a cause, or causes of some sort; but if we have previously given the name of matter, with direct reference to the one set of effects, and not with direct reference to the other, it necessarily follows, that, in relation to matter, as often as we speak or think of it, the qualities which correspond with the one set of effects, that have led us to use that name, must be regarded by us as primary, and the others, which may, or may not coexist with these, only as secondary. An external body may, or may not be fragrant, because fragrance is not one of the qualities previously included by us in our definition of a body; but it _must_ be _extended_, and present an obstacle to our compressing force, because these are the very qualities, which we have included in our definition, and without which, therefore, the definition must cease to be applicable to the thing defined.

If, originally, we had invented the word _matter_ to denote the cause, whatever it might be, of our sensations of smell, it is very evident, that _fragrance_ would then have been to us the primary quality of _matter_, as being that which was essential to our definition of matter,--and all other qualities, by which the cause of smell might, or might not at the same time affect our other senses, would then have been _secondary_ qualities only,--as being qualities compatible with our definition of matter, but not essential to it.

What we now term matter, however, I have repeatedly observed,--is that which we consider as _occupying space_, and _resisting our effort to compress it_; and those qualities of matter may well be said to be primary, by which matter itself, as thus defined, becomes known to us,--or by the union of which, in our conception, we form the complex notion of matter, and give or withhold that name according as these qualities are present or absent. Extension and resistance are the distinguishing qualities that direct us in all our applications of the word which comprehends them. They are truly _primary_ qualities, therefore; since, without our consideration of them, we never could have formed the complex notion of the substance itself, to which we afterwards, in our analysis of that complex notion, ascribe them separately as qualities;--and all the other qualities, which we may afterwards find occasion to refer to an extended resisting substance, must evidently be secondary, in reference to those qualities, without which as previously combined in our thought, we could not have had the primary notion of the substance to which we thus secondarily refer them. If, in the case which we have already frequently imagined, of the single sense of smell, we had been absolutely unsusceptible of every other external feeling, we might, indeed, have considered our sensation as the effect of _some_ cause,--and even of a cause that was different from our mind itself; but it is very evident that we could not have considered it as the effect of the presence of _matter_, at least as that term is now understood by us. If, in these circumstances,--after frequent repetition of the fragrance, as the only quality of bodies with which we could be acquainted,--we were to acquire in an instant all the other senses which we now possess,--so as to become capable of forming that complex notion of things extended and resisting, which is our present notion of matter, we should then, indeed, have a fuller notion of the rose, of the mere fragrance of which we before were sensible, without knowing of what it was the fragrance, and might learn to refer the fragrance to the rose, by the same coexistences of sensations which have led us, in our present circumstances, to combine the fragrance with other qualities, in the complex conception of the flower. Even then, however, though the fragrance, which was our first sensation, had truly been known to us before the other qualities, and though the sensation, therefore, would deserve the name of primary, the _reference_ of this earlier feeling to the external rose as its cause, would still truly be _secondary_ to the earlier reference, or rather to the earlier combination of other qualities, in one complex whole, by which we had formed to ourselves the notion of the extended and resisting rose, as a body, that admitted the subsequent reference of the delightful sensation of fragrance to be made to it, as the equal cause of these different effects.

In this sense, then, the distinction of the primary and secondary qualities of matter is just,--that, whatever qualities we refer to a _material_ cause must be, in reference, secondary to those qualities that are essential to our very notion of the body, to which the subsequent reference of the other qualities is made. We have formed our definition of matter; and, as in every other definition of every sort, the qualities included in the definition, must always, in comparison of other qualities, be primary and essential, relatively to the thing defined.

Nor is this all.--It will be admitted likewise, that the qualities termed _primary_,--which alone are included in our general definitions of matter, and which are all, as we have seen, modifications of mere extension and resistance, are, even after we have learned to consider the causes of all our sensations as substances external to the mind, still felt by us to be external, with more clearness and vividness, than the other qualities, which we term _secondary_. The difference is partly, and chiefly, in the nature of the sensations themselves, as already explained to you, but depends also, I conceive, in no inconsiderable degree, on the permanence and universality of the objects which possess the primary qualities, and the readiness with which we can renew our feeling of them at will, from the constant presence of our own bodily frame, itself extended and resisting, and of the other causes of these feelings of extension and resistance, that seem to be every where surrounding us. Tastes, smells, sounds,--even colours though more lasting than these--are not always before us;--but there is not a moment at which we cannot, by the mere stretching of our hand, produce at pleasure, the feeling of something extended and resisting. It is a very natural effect of this difference, that the one set of causes which are always before us, should seem to us, therefore, peculiarly permanent, and the other set, that are only occasionally present, should seem almost as fugitive as our sensations themselves.

In these most important respects, there is, then, a just ground for the distinction of the primary from the secondary qualities of bodies. They are primary in the order of our definition of matter; and they are felt by us as peculiarly permanent, independently of our feelings, which they seem at every moment ready to awake. The power of affecting us with smell, taste, sight, or hearing, may or may not be present; but the power of exciting the feelings of extension and resistance is constantly present, and is regarded by us as essential to our very notion of matter,--or, in other words, we give the name of _matter_, only where this complex perception is excited in us. We seem, therefore, to be constantly surrounded with a material world of substances extended and resisting, that is to say, a world of substances capable of exciting in us the feelings which are ascribed to the primary quality of matter;--but still the feeling of these primary qualities, which we regard as permanent, is not less than the feeling of the secondary qualities, a state or affection of the mind, and nothing more;--and in the one case, as much as in the other, in the perception of the qualities termed secondary, as much as of the qualities termed primary, the feeling, when it occurs, is the direct or immediate result of the presence of the external body with the quality of which it corresponds;--or, if there be any difference in this respect, I conceive that our feeling of fragrance, or sweetness, was, originally at least, a more immediate result of the presence of odorous or sapid particles,--than any feeling of extension, without the mind, was the effect of the first body which we touched.