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Of the External Senses - Adam Smith, Glasgow Edition of the Works and Correspondence Vol. 3 Essays on Philosophical Subjects 
Essays on Philosophical Subjects, ed. W. P. D. Wightman and J. C. Bryce, vol. III of the Glasgow Edition of the Works and Correspondence of Adam Smith (Indianapolis: Liberty Fund, 1982).
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Of the External Senses
Of all the Essays on Philosophical Subjects this alone might pass for philosophical in the more restricted sense now current. At any rate it is written in the style we have come to associate with the great philosophical classics of the period beginning with Descartes: characterized by ‘full and accurate expression’ and ‘clear illustration’ and controlled by a more adequate acquaintance with the relevant facts of ‘natural philosophy’ than is evident in much of the ‘philosophical’ writing of the recent past. Yet of all the essays it is the most difficult to assess. Neither in its title nor in its text is there any hint of what part, if any, Smith intended it to play in his ‘grand design’; it is devoid alike of any reference to historical development or ‘principles of philosophical investigation’. In the absence of any certain evidence that it was written at, or even near, the same time as the ‘historical’ essays it is perhaps best to regard it as literally an essai or attempt to set out the author’s ideas on a subject that remained of central concern throughout his lifetime. Thus it could not avoid being derived from Locke’s Essay, which it resembles in being set forth in the same ‘historical plain method’. The Cartesian ‘machine’ theory of sensation (in a corpuscularian variant) is given cautious acceptance. But neither Locke nor anyone else (except a passing reference to Gassendi and Newton) is mentioned until the ‘Sense of Seeing’ is discussed; here Smith refers at once to Berkeley’s ‘New Theory of Vision, one of the finest examples of philosophical analysis that is to be found, either in our own, or in any other language’ (External Senses, 43). Unfortunately, he does not seem to realize that Berkeley’s analysis had vitiated1 the distinction between primary and secondary qualities which he is at pains to establish in the first sixteen pages of his own essay. It is therefore probable that he wrote the essay before digesting Hume’s Treatise (1739) or even before becoming closely acquainted with Hume, as there is reason to believe he did before 1752 (Stewart, I.13).
Though not unambiguously related to Smith’s ‘grand design’, this essay is not without significance for the general assessment of his appreciation of the nature of ‘philosophical’ thinking. With the exception just noted it would pass for a very fair résumé of the contemporary state of knowledge of the ‘external senses’, such as might have provided an encyclopedia article, and looked at of course from the point of view of philosophical psychology rather than that of natural philosophy; as such it is no more than competent. There are, however, two sections of considerable significance for any assessment of Smith’s own intellectual development as also of his place in the history of ideas.
The first of these sections begins at §60, where Smith seizes on Berkeley’s ingenious theory (New Theory of Vision, 139–47, and Principles of Human Knowledge, 30–1) of regarding the association and sequence of ‘external’ sensations or ideas as a language employed by ‘the Author of our being’ to guide our behaviour as may best conduce to the welfare of our bodies and minds. In the course of his exposition Berkeley had considered the analogous relationship between ‘signs’ (letters and words) and objects in languages of human origin and use. Smith was to consider this correspondence in greater depth in Considerations concerning the First Formation of Languages, first published in 1761. Professor Ralph Lindgren has seen in this frequent reference to linguistic origin and structure a major factor in Smith’s whole methodology.2
The other section of special significance in this essay is comprised in the concluding pages where a side of Smith’s genius is revealed for which the other ‘philosophical’ essays had given no scope: this was his appeal to careful ‘field’ observations on animals in which he displays an appreciation of the power of the comparative method to correlate data and control theory.
of the EXTERNAL SENSES
The Senses, by which we perceive external objects, are commonly reckoned Five in Number; Seeing, Hearing, Smelling, Tasting, and Touching.
Of these, the four first mentioned are each of them confined to particular parts or organs of the body; the Sense of Seeing is confined to the Eyes; that of Hearing to the Ears; that of Smelling to the Nostrils; and that of Tasting to the Palate. The Sense of Touching alone seems not to be confined to any particular organ, but to be diffused through almost every part of the body; if we except the hair and the nails of the fingers and toes, I believe through every part of it. I shall say a few words concerning each of these Senses; beginning with the last, proceeding backwards in the opposite order to that in which they are commonly enumerated.
Of the Sense ofTouching
The objects of Touch always present themselves as pressing upon, or as resisting the particular part of the body which perceives them, or by which we perceive them. When I lay my hand upon the table, the table presses upon my hand, or resists the further motion of my hand, in the same manner as my hand presses upon the table. But pressure or resistance necessarily supposes externality in the thing which presses or resists. The table could not press upon, or resist the further motion of my hand, if it was not external to my hand. I feel it accordingly, as something which is not merely an affection of my hand, but altogether external to, and independant of my hand. The agreeable, indifferent, or painful sensation of pressure, according as I happen to press hardly or softly, I feel, no doubt, as affections of my hand; but the thing which presses and resists I feel as something altogether different from those affections, as external to my hand, and as altogether independent of it.
In moving my hand along the table it soon comes, in every direction, to a place where this pressure or resistance ceases. This place we call the boundary, or end of the table; of which the extent and figure are determined by the extent and direction of the lines or surfaces which constitute this boundary or end.
It is in this manner that a man born blind, or who has lost his sight so early that he has no remembrance of visible objects, may form the most distinct idea of the extent and figure of all the different parts of his own body, and of every other tangible object which he has an opportunity of handling and examining. When he lays his hand upon his foot, as his hand feels the pressure or resistance of his foot, so his foot feels that of his hand. They are both external to one another, but they are, neither of them, altogether so external to him. He feels in both, and he naturally considers them as parts of himself, or at least as something which belongs to him, and which, for his own happiness and comfort, it is necessary that he should take some care of.
When he lays his hand upon the table, though his hand feels the pressure of the table, the table does not feel, at least he does not know that it feels, the pressure of his hand. He feels it therefore as something external, not only to his hand, but to himself, as something which makes no part of himself, and in the state and condition of which he has not necessarily any concern.
When he lays his hand upon the body either of another man, or of any other animal, though he knows, or at least may know, that they feel the pressure of his hand as much as he feels that of their body: Yet as this feeling is altogether external to him, he frequently gives no attention to it, and at no time takes any further concern in it than he is obliged to do by that fellow–feeling which Nature has, for the wisest purposes, implanted in man, not only towards all other men, but (though no doubt in a much weaker degree) towards all other animals. Having destined him to be the governing animal in this little world, it seems to have been her benevolent intention to inspire him with some degree of respect, even for the meanest and weakest of his subjects.
This power or quality of resistance we call Solidity; and the thing which possesses it, the Solid Body or Thing. As we feel it as something altogether external to us, so we necessarily conceive it as something altogether independent of us. We consider it, therefore, as what we call a Substance, or as a thing that subsists by itself, and independent of any other thing. Solid and substantial, accordingly, are two words which, in common language, are considered either as altogether, or as nearly synonimous.
Solidity necessarily supposes some degree of extension, and that in all the three directions of length, breadth, and thickness. All the solid bodies, of which we have any experience, have some degree of such bulk or magnitude. It seems to be essential to their nature, and without it, we cannot even conceive how they should be capable of pressure or resistance;1 the powers by which they are made known to us, and by which alone they are capable of acting upon our own, and upon all other bodies.
Extension, at least any sensible extension, supposes divisibility. The body may be so hard, that our strength is not sufficient to break it: we still suppose, however, that if a sufficient force were applied, it might be so broken; and, at any rate, we can always, in fancy at least, imagine it to be divided into two or more parts.
Every solid and extended body, if it be not infinite, (as the universe may be conceived to be,) must have some shape or figure, or be bounded by certain lines and surfaces.
Every such body must likewise be conceived as capable both of motion and of rest; both of altering its situation with regard to other surrounding bodies, and of remaining in the same situation. That bodies of small or moderate bulk, are capable of both motion and rest we have constant experience. Great masses, perhaps, are, according to the ordinary habits of the imagination, supposed to be more fitted for rest than for motion.2 Provided a sufficient force could be applied, however, we have no difficulty in conceiving that the greatest and most unwieldy masses might be made capable of motion. Philosophy teaches us, (and by reasons too to which it is scarcely possible to refuse our assent,) that the earth itself, and bodies much larger than the earth, are not only moveable, but are at all times actually in motion, and continually altering their situation, in respect to other surrounding bodies, with a rapidity that almost passes all human comprehension. In the system of the universe, at least according to the imperfect notions which we have hitherto been able to attain concerning it, the great difficulty seems to be, not to find the most enormous masses in motion, but to find the smallest particle of matter that is perfectly at rest, with regard to all other surrounding bodies.3
These four qualities, or attributes of extension, divisibility, figure, and mobility, or the capacity of motion or rest, seem necessarily involved in the idea or conception of a solid substance. They are, in reality, inseparable from that idea or conception, and the solid substance cannot possibly be conceived to exist without them. No other qualities or attributes seem to be involved, in the same manner, in this our idea or conception of solidity. It would, however, be rash from thence to conclude that the solid substance can, as such, possess no other qualities or attributes. This very rash conclusion, notwithstanding, has been not only drawn, but insisted upon, as an axiom of the most indubitable certainty, by philosophers of very eminent reputation.4
Of these external and resisting substances, some yield easily, and change their figure, at least in some degree, in consequence of the pressure of our hand: others neither yield nor change their figure, in any respect, in consequence of the utmost pressure which our hand alone is capable of giving them. The former we call soft, the latter hard, bodies. In some bodies the parts are so very easily separable, that they not only yield to a very moderate pressure, but easily receive the pressing body within them, and without much resistance allow it to traverse their extent in every possible direction. These are called Fluid, in contradistinction to those of which the parts not being so easily separable, are upon that account peculiarly called Solid Bodies; as if they possessed, in a more distinct and perceptible manner, the characteristical quality of solidity or the power of resistance. Water, however, (one of the fluids with which we are most familiar,) when confined on all sides, (as in a hollow globe of metal, which is first filled with it, and then sealed hermetically,) has been found to resist pressure as much as the hardest, or what we commonly call the most solid bodies.
Some fluids yield so very easily to the slightest pressure, that upon ordinary occasions we are scarcely sensible of their resistance; and are upon that account little disposed to conceive them as bodies, or as things capable of pressure and resistance. There was a time, as we may learn from Aristotle and Lucretius,5 when it was supposed to require some degree of philosophy to demonstrate that air was a real solid body, or capable of pressure and resistance. What, in ancient times, and in vulgar apprehensions, was supposed to be doubtful with regard to air, still continues to be so with regard to light, of which the rays, however condensed or concentrated, have never appeared capable of making the smallest resistance to the motion of other bodies, the characteristical power or quality of what are called bodies, or solid substances. Some philosophers accordingly doubt, and some even deny, that light is a material or corporeal substance.6
Though all bodies or solid substances resist, yet all those with which we are acquainted appear to be more or less compressible, or capable of having, without any diminution in the quantity of their matter, their bulk more or less reduced within a smaller space than that which they usually occupy. An experiment of the Florentine academy7 was supposed to have demonstrated that water was absolutely incompressible. The same experiment, however, having been repeated with more care and accuracy, it appears, that water, though it strongly resists compression, is, however, when a sufficient force is applied, like all other bodies, in some degree liable to it. Air, on the contrary, by the application of a very moderate force, is easily reducible within a much smaller portion of space than that which it usually occupies. The condensing engine, and what is founded upon it, the wind–gun, sufficiently demonstrate this: and even without the help of such ingenious and expensive machines, we may easily satisfy ourselves of the truth of it, by squeezing a full–blown bladder of which the neck is well tied.
The hardness or softness of bodies, or the greater or smaller force with which they resist any change of shape, seems to depend altogether upon the stronger or weaker degree of cohesion with which their parts are mutually attracted to one another. The greater or smaller force with which they resist compression may, upon many occasions, be owing partly to the same cause: but it may likewise be owing to the greater or smaller proportion of empty space comprehended within their dimensions, or intermixed with the solid parts which compose them. A body which comprehended no empty space within its dimensions, which, through all its parts, was completely filled with the resisting substance, we are naturally disposed to conceive as something which would be absolutely incompressible, and which would resist, with unconquerable force, every attempt to reduce it within narrower dimensions. If the solid and resisting substance, without moving out of its place, should admit into the same place another solid and resisting substance, it would from that moment, in our apprehension, cease to be a solid and resisting substance, and would no longer appear to possess that quality, by which alone it is made known to us, and which we therefore consider as constituting its nature and essence, and as altogether inseparable from it. Hence our notion of what has been called impenetrability of matter; or of the absolute impossibility that two solid resisting substances should occupy the same place at the same time.
This doctrine, which is as old as Leucippus, Democritus, and Epicurus, was in the last century revived by Gassendi,8 and has since been adopted by Newton and the far greater part of his followers. It may at present be considered as the established system, or as the system that is most in fashion, and most approved of by the greater part of the philosophers of Europe. Though it has been opposed by several puzzling arguments, drawn from that species of metaphysics which confounds every thing and explains nothing, it seems upon the whole to be the most simple, the most distinct, and the most comprehensible account that has yet been given of the phaenomena which are meant to be explained by it. I shall only observe, that whatever system may be adopted concerning the hardness or softness, the fluidity or solidity, the compressibility or incompressibility, of the resisting substance, the certainty of our distinct sense and feeling of its Externality, or of its entire independency upon the organ which perceives it, or by which we perceive it, cannot in the smallest degree be affected by any such system. I shall not therefore attempt to give any further account of such systems.
Heat and cold being felt by almost every part of the human body, have commonly been ranked along with solidity and resistance, among the qualities which are the objects of Touch. It is not, however, I think, in our language proper to say that we touch, but that we feel, the qualities of heat and cold. The word feeling, though in many cases we use it as synonimous to touching, has, however, a much more extensive signification, and is frequently employed to denote our internal, as well as our external, affections. We feel hunger and thirst, we feel joy and sorrow, we feel love and hatred.
Heat and cold, in reality, though they may frequently be perceived by the same parts of the human body, constitute an order of sensations altogether different from those which are the proper objects of Touch. They are naturally felt, not as pressing upon the organ, but as in the organ. What we feel while we stand in the sunshine during a hot, or in the shade during a frosty, day, is evidently felt, not as pressing upon the body, but as in the body. It does not necessarily suggest the presence of any external object, nor could we from thence alone infer the existence of any such object. It is a sensation which neither does nor can exist any where but either in the organ which feels it, or in the unknown principle of perception, whatever that may be, which feels in that organ, or by means of that organ. When we lay our hand upon a table, which is either heated or cooled a good deal beyond the actual temperature of our hand, we have two distinct perceptions: first, that of the solid or resisting table, which is necessarily felt as something external to, and independent of, the hand which feels it: and secondly, that of the heat or cold, which by the contact of the table is excited in our hand, and which is naturally felt as nowhere but in our hand, or in the principle of perception which feels in our hand.9
But though the sensations of heat and cold do not necessarily suggest the presence of any external object, we soon learn from experience that they are commonly excited by some such object; sometimes by the temperature of some external body immediately in contact with our own body, and sometimes by some body at either a moderate or a great distance from us; as by the fire in a chamber, or by the sun in a Summer’s day. By the frequency and uniformity of this experience, by the custom and habit of thought which that frequency and uniformity necessarily occasion, the Internal Sensation, and the External Cause of that Sensation, come in our conception to be so strictly connected, that in our ordinary and careless way of thinking, we are apt to consider them as almost one and the same thing, and therefore denote them by one and the same word. The confusion, however, is in this case more in the word than in the thought; for in reality we still retain some notion of the distinction, though we do not always evolve it with that accuracy which a very slight degree of attention might enable us to do. When we move our hand, for example, along the surface of a very hot or of a very cold table, though we say that the table is hot or cold in every part of it, we never mean that, in any part of it, it feels the sensations either of heat or of cold, but that in every part of it, it possesses the power of exciting one or other of those sensations in our bodies. The philosophers who have taken so much pains to prove that there is no heat in the fire, meaning that the sensation or feeling of heat is not in the fire, have laboured to refute an opinion which the most ignorant of mankind never entertained. But the same word being, in common language, employed to signify both the sensation and the power of exciting that sensation, they, without knowing it perhaps, or intending it, have taken advantage of this ambiguity, and have triumphed in their own superiority, when by irresistible arguments they establish an opinion which, in words indeed, is diametrically opposite to the most obvious judgments of mankind, but which in reality is perfectly agreeable to those judgments.
Of the Sense ofTasting
When we taste any solid or liquid substance, we have always two distinct perceptions; first, that of the solid or liquid body, which is naturally felt as pressing upon, and therefore as external to, and independent of, the organ which feels it; and secondly, that of the particular taste, relish, or savour which it excites in the palate or organ of Tasting, and which is naturally felt, not as pressing upon, as external to, or as independent of, that organ; but as altogether in the organ, and nowhere but in the organ, or in the principle of perception which feels in that organ. When we say that the food which we eat has an agreeable or disagreeable taste in every part of it, we do not thereby mean that it has the feeling or sensation of taste in any part of it, but that in every part of it, it has the power of exciting that feeling or sensation in our palates. Though in this case we denote by the same word (in the same manner, and for the same reason, as in the case of heat and cold) both the sensation and the power of exciting that sensation, this ambiguity of language misleads the natural judgments of mankind in the one case as little as in the other. Nobody ever fancies that our food feels its own agreeable or disagreeable taste.
Of the Sense ofSmelling
Every smell or odour is naturally felt as in the nostrils;10 not as pressing upon or resisting the organ, not as in any respect external to, or independent of, the organ, but as altogether in the organ, and nowhere else but in the organ, or in the principle of perception which feels in that organ. We soon learn from experience, however, that this sensation is commonly excited by some external body; by a flower, for example, of which the absence removes, and the presence brings back, the sensation. This external body we consider as the cause of this sensation, and we denominate by the same words both the sensation and the power by which the external body produces this sensation. But when we say that the smell is in the flower, we do not thereby mean that the flower itself has any feeling of the sensation which we feel; but that it has the power of exciting this sensation in our nostrils, or in the principle of perception which feels in our nostrils. Though the sensation, and the power by which it is excited, are thus denoted by the same word, this ambiguity of language misleads, in this case, the natural judgments of mankind as little as in the two preceding.
Of the Sense ofHearing
Every sound is naturally felt as in the Ear, the organ of Hearing.11 Sound is not naturally felt as resisting or pressing upon the organ, or as in any respect external to, or independent of, the organ. We naturally feel it as an affection of our Ear, as something which is altogether in our Ear, and nowhere but in our Ear, or in the principle of perception which feels in our Ear. We soon learn from experience, indeed, that the sensation is frequently excited by bodies at a considerable distance from us; often at a much greater distance than those ever are which excite the sensation of Smelling. We learn too from experience, that this sound or sensation in our Ears receives different modifications, according to the distance and direction of the body which originally causes it. The sensation is stronger, the sound is louder, when that body is near. The sensation is weaker, the sound is lower, when that body is at a distance. The sound, or sensation, too undergoes some variation according as the body is placed on the right hand or on the left, before or behind us. In common language we frequently say, that the sound seems to come from a great or from a small distance, from the right hand or from the left, from before or from behind us. We frequently say too that we hear a sound at a great or a small distance, on our right hand or on our left. The real sound, however, the sensation in our ear, can never be heard or felt any where but in our ear, it can never change its place, it is incapable of motion, and can come, therefore, neither from the right nor from the left, neither from before nor from behind us. The Ear can feel or hear nowhere but where it is, and cannot stretch out its powers of perception, either to a great or to a small distance, either to the right or to the left. By all such phrases we in reality mean nothing but to express our opinion concerning either the distance, or the direction of the body, which excites the sensation of sound. When we say that the sound is in the bell, we do not mean that the bell hears its own sound, or that any thing like our sensation is in the bell, but that it possesses the power of exciting that sensation in our organ of Hearing. Though in this, as well as in some other cases, we express by the same word, both the Sensation, and the Power of exciting that Sensation; this ambiguity of language occasions scarce any confusion in the thought, and when the different meanings of the word are properly distinguished, the opinions of the vulgar, and those of the philosopher, though apparently opposite, turn out to be exactly the same.
These four classes of secondary qualities, as philosophers have called them, or to speak more properly, these four classes of Sensations; Heat and Cold, Taste, Smell, and Sound; being felt, not as resisting or pressing upon the organ; but as in the organ, are not naturally perceived as external and independant substances; or even as qualities of such substances; but as mere affections of the organ, and what can exist nowhere but in the organ.
They do not possess, nor can we even conceive them as capable of possessing, any one of the qualities, which we consider as essential to, and inseparable from, the external solid and independant substances.
First, They have no extension. They are neither long nor short; they are neither broad nor narrow; they are neither deep nor shallow. The bodies which excite them, the spaces within which they may be perceived, may possess any of those dimensions; but the Sensations themselves can possess none of them. When we say of a Note in Music, that it is long or short, we mean that it is so in point of duration. In point of extension we cannot even conceive, that it should be either the one or the other.
Secondly, Those Sensations have no figure. They are neither round nor square, though the bodies which excite them, though the spaces within which they may be perceived, may be either the one or the other.
Thirdly, Those Sensations are incapable of motion. The bodies which excite them may be moved to a greater or to a smaller distance. The Sensations become fainter in the one case, and stronger in the other. Those bodies may change their direction with regard to the organ of Sensation. If the change be considerable, the Sensations undergo some sensible variation in consequence of it. But still we never ascribe motion to the Sensations. Even when the person who feels any of those Sensations, and consequently the organ by which he feels them, changes his situation, we never, even in this case, say, that the Sensation moves, or is moved. It seems to exist always, where alone it is capable of existing, in the organ which feels it. We never even ascribe to those Sensations the attribute of rest; because we never say that any thing is at rest, unless we suppose it capable of motion. We never say that any thing does not change its situation with regard to other things, unless we suppose it capable of changing that situation.
Fourthly, Those Sensations, as they have no extension, so they can have no divisibility. We cannot even conceive that a degree of Heat or Cold, that a Smell, a Taste, or a Sound, should be divided (in the same manner as the solid and extended substance may be divided) into two halves, or into four quarters, or into any other number of parts.
But though all these Sensations are equally incapable of division; there are three of them, Taste, Smell, and Sound; which seem capable of a certain composition and decomposition. A skilful cook will, by his taste, perhaps, sometimes distinguish the different ingredients, which enter into the composition of a new sauce, and of which the simple tastes make up the compound one of the sauce. A skilful perfumer may, perhaps, sometimes be able to do the same thing with regard to a new Scent. In a concert of vocal and instrumental music, an acute and experienced Ear readily distinguishes all the different sounds which strike upon it at the same time, and which may, therefore, be considered as making up one compound sound.
Is it by nature, or by experience, that we learn to distinguish between simple and compound Sensations of this kind? I am disposed to believe that it is altogether by experience; and that naturally all Tastes, Smells, and Sounds, which affect the organ of Sensation at the same time, are felt as simple and uncompounded Sensations. It is altogether by experience, I think, that we learn to observe the different affinities and resemblances which the compound Sensation bears to the different simple ones, which compose it, and to judge that the different causes, which naturally excite those different simple Sensations, enter into the composition of that cause which excites the compounded one.
It is sufficiently evident that this composition and decomposition is altogether different from that union and separation of parts, which constitutes the divisibility of solid extension.
The Sensations of Heat and Cold seem incapable even of this species of composition and decomposition. The Sensations of Heat and Cold may be stronger at one time and weaker at another. They may differ in degree, but they cannot differ in kind. The Sensations of Taste, Smell, and Sound, frequently differ, not only in degree, but in kind. They are not only stronger and weaker, but some Tastes are sweet and some bitter; some Smells are agreeable, and some offensive; some Sounds are acute, and some grave; and each of these different kinds or qualities too is capable of an immense variety of different modifications. It is the combination of such simple Sensations, as differ not only in degree but in kind, which constitutes the compounded Sensation.
These four classes of Sensations, therefore, having none of the qualities which are essential to, and inseparable from, the solid, external, and independant substances which excite them, cannot be qualities or modifications of those substances. In reality we do not naturally consider them as such; though in the way in which we express ourselves on the subject, there is frequently a good deal of ambiguity and confusion. When the different meanings of words, however, are fairly distinguished, these Sensations are, even by the most ignorant and illiterate, understood to be, not the qualities, but merely the effects of the solid, external, and independant substances upon the sensible and living organ, or upon the principle of perception which feels in that organ.
Philosophers, however, have not in general supposed that those exciting bodies produce those Sensations immediately, but by the intervention of one, two, or more intermediate causes.
In the Sensation of Taste, for example, though the exciting body presses upon the organ of Sensation, this pressure is not supposed to be the immediate cause of the Sensation of Taste. Certain juices of the exciting body are supposed to enter the pores of the palate, and to excite, in the irritable and sensible fibres of that organ, certain motions or vibrations, which produce there the Sensation of Taste. But how those juices should excite such motions, or how such motions should produce, either in the organ, or in the principle of perception which feels in the organ, the Sensation of Taste; or a Sensation, which not only does not bear the smallest resemblance to any motion, but which itself seems incapable of all motion, no philosopher has yet attempted, nor probably ever will attempt to explain to us.
The Sensations of Heat and Cold, of Smell and Sound, are frequently excited by bodies at a distance, sometimes at a great distance, from the organ which feels them. But it is a very antient and well–established axiom in metaphysics, that nothing can act where it is not;12 and this axiom, it must, I think, be acknowledged, is at least perfectly agreeable to our natural and usual habits of thinking.
The Sun, the great source of both Heat and Light, is at an immense distance from us. His rays, however, (traversing, with inconceivable rapidity, the immensity of the intervening regions,) as they convey the Sensation of Light to our eyes, so they convey that of Heat to all the sensible parts of our body. They even convey the power of exciting that Sensation to all the other bodies that surround us. They warm the earth, and air, we say; that is, they convey to the earth and the air the power of exciting that Sensation in our bodies. A common fire produces, in the same manner, all the same effects; though the sphere of its action is confined within much narrower limits.
The odoriferous body, which is generally too at some distance from us, is supposed to act upon our organs by means of certain small particles of matter, called Effluvia, which being sent forth in all possible directions, and drawn into our nostrils by the inspiration of breathing, produce there the Sensation of Smell. The minuteness of those small particles of matter, however, must surpass all human comprehension. Inclose in a gold box, for a few hours, a small quantity of musk. Take out the musk, and clean the box with soap and water as carefully as it is possible. Nothing can be supposed to remain in the box, but such effluvia as, having penetrated into its interior pores, may have escaped the effects of this cleansing. The box, however, will retain the smell of musk for many, I do not know for how many years; and these effluvia, how minute soever we may suppose them, must have had the powers of subdividing themselves, and of emitting other effluvia of the same kind, continually, and without any interruption, during so long a period. The nicest balance, however, which human art has been able to invent, will not show the smallest increase of weight in the box immediately after it has been thus carefully cleaned.
The Sensation of Sound is frequently felt at a much greater distance from the sounding, than that of Smell ever is from the odoriferous body. The vibrations of the sounding body, however, are supposed to produce certain correspondent vibrations and pulses in the surrounding atmosphere, which being propagated in all directions, reach our organ of Hearing, and produce there the Sensation of Sound. There are not many philosophical doctrines, perhaps, established upon a more probable foundation, than that of the propagation of Sound by means of the pulses or vibrations of the air. The experiment of the bell, which, in an exhausted receiver, produces no sensible Sound, would alone render this doctrine somewhat more than probable. But this great probability is still further confirmed by the computations of Sir Isaac Newton,13 who has shown that, what is called the velocity of Sound, or the time which passes between the commencement of the action of the sounding body, and that of the Sensation in our ear, is perfectly suitable to the velocity with which the pulses and vibrations of an elastic fluid of the same density with the air, are naturally propagated. Dr. Franklin has made objections to this doctrine, but, I think, without success.14
Such are the intermediate causes by which philosophers have endeavoured to connect the Sensations in our organs, with the distant bodies which excite them. How those intermediate causes, by the different motions and vibrations which they may be supposed to excite on our organs, produce there those different Sensations, none of which bear the smallest resemblance to vibration or motion of any kind, no philosopher has yet attempted to explain to us.
Of the Sense ofSeeing
Dr. Berkley,15 in his New Theory of Vision, one of the finest examples of philosophical analysis that is to be found, either in our own, or in any other language, has explained, so very distinctly, the nature of the objects of Sight: their dissimilitude to, as well as their correspondence and connection with those of Touch, that I have scarcely any thing to add to what he has already done. It is only in order to render some things, which I shall have occasion to say hereafter, intelligible to such readers as may not have had an opportunity of studying his book, that I have presumed to treat of the same subject, after so great a Master. Whatever I shall say upon it, if not directly borrowed from him, has at least been suggested by what he has already said.
That the objects of Sight are not perceived as resisting or pressing upon the organ which perceives them, is sufficiently obvious. They cannot therefore suggest, at least in the same manner, as the objects of Touch, the externality and independency of their existence.
We are apt, however, to imagine that we see objects at a distance from us, and that consequently the externality of their existence is immediately perceived by our Sight. But if we consider that the distance of any object from the eye, is a line turned endways to it; and that this line must consequently appear to it, but as one point; we shall be sensible that distance from the eye cannot be the immediate object of Sight, but that all visible objects must naturally be perceived as close upon the organ, or more properly, perhaps, like all other Sensations, as in the organ which perceives them.16 That the objects of Sight are all painted in the bottom of the eye, upon a membrane called the retina, pretty much in the same manner as the like objects are painted in a Camera Obscura, is well known to whoever has the slightest tincture of the science of Optics; and the principle of perception, it is probable, originally perceives them, as existing in that part of the organ, and nowhere but in that part of the organ. No Optician, accordingly, no person who has ever bestowed any moderate degree of attention upon the nature of Vision, has ever pretended that distance from the eye was the immediate object of Sight. How it is that, by means of our Sight, we learn to judge of such distances, Opticians have endeavoured to explain in several different ways. I shall not, however, at present, stop to examine their systems.
The objects of Touch are solidity, and those modifications of solidity which we consider as essential to it, and inseparable from it; solid extension, figure, divisibility, and mobility.
The objects of Sight are colour, and those modifications of colour which, in the same manner, we consider as essential to it, and inseparable from it; coloured extension, figure, divisibility, and mobility. When we open our eyes, the sensible coloured objects, which present themselves to us, must all have a certain extension, or must occupy a certain portion of the visible surface which appears before us. They must too have all a certain figure, or must be bounded by certain visible lines, which mark upon that surface the extent of their respective dimensions. Every sensible portion of this visible or coloured extension must be conceived as divisible, or as separable into two, three, or more parts. Every portion too of this visible or coloured surface must be conceived as moveable, or as capable of changing its situation, and of assuming a different arrangement with regard to the other portions of the same surface.
Colour, the visible, bears no resemblance to solidity, the tangible object. A man born blind, or who has lost his Sight so early as to have no remembrance of visible objects, can form no idea or conception of colour. Touch alone can never help him to it. I have heard, indeed, of some persons who had lost their Sight after the age of manhood, and who had learned to distinguish, by the Touch alone, the different colours of cloths or silks, the goods which it happened to be their business to deal in. The powers by which different bodies excite in the organs of Sight the Sensations of different colours, probably depend upon some difference in the nature, configuration, and arrangement of the parts which compose their respective surfaces. This difference may, to a very nice and delicate touch, make some difference in the feeling, sufficient to enable a person, much interested in the case, to make this distinction in some degree, though probably in a very imperfect and inaccurate one. A man born blind might possibly be taught to make the same distinctions. But though he might thus be able to name the different colours, which those different surfaces reflected, though he might thus have some imperfect notion of the remote causes of these Sensations, he could have no better idea of the Sensations themselves, than that other blind man, mentioned by Mr. Locke,17 had, who said that he imagined the Colour of Scarlet resembled the Sound of a Trumpet. A man born deaf may, in the same manner, be taught to speak articulately. He is taught how to shape and dispose of his organs, so as to pronounce each letter, syllable, and word. But still, though he may have some imperfect idea of the remote causes of the Sounds which he himself utters, of the remote causes of the Sensations which he himself excites in other people; he can have none of those Sounds or Sensations themselves.
If it were possible, in the same manner, that a man could be born without the Sense of Touching, that of Seeing could never alone suggest to him the idea of Solidity, or enable him to form any notion of the external and resisting substance. It is probable, however, not only that no man, but that no animal was ever born without the Sense of Touching, which seems essential to, and inseparable from, the nature of animal life and existence. It is unnecessary, therefore, to throw away any reasoning, or to hazard any conjectures, about what might be the effects of what I look upon as altogether an impossible supposition. The eye when pressed upon by any external and solid substance, feels, no doubt, that pressure and resistance, and suggests to us (in the same manner as every other feeling part of the body) the external and independent existence of that solid substance. But in this case, the eye acts, not as the organ of Sight, but as an organ of Touch; for the eye possesses the Sense of Touching in common with almost all the other parts of the body.
The extension, figure, divisibility, and mobility of Colour, the sole object of Sight, though, on account of their correspondence and connection with the extension, figure, divisibility, and mobility of Solidity, they are called by the same name, yet seem to bear no sort of resemblance to their namesakes. As Colour and Solidity bear no sort of resemblance to one another, so neither can their respective modifications. Dr. Berkley very justly observes,18 that though we can conceive either a coloured or a solid line to be prolonged indefinitely, yet we cannot conceive the one to be added to the other. We cannot, even in imagination, conceive an object of Touch to be prolonged into an object of Sight, or an object of Sight into an object of Touch. The objects of Sight and those of Touch constitute two worlds, which, though they have a most important correspondence and connection with one another, bear no sort of resemblance to one another. The tangible world, as well as all the different parts which compose it, has three dimensions, Length, Breadth, and Depth. The visible world, as well as all the different parts which compose it, has only two, Length and Breadth. It presents to us only a plain or surface, which, by certain shades and combinations of Colour, suggests and represents to us (in the same manner as a picture does) certain tangible objects which have no Colour, and which therefore can bear no resemblance to those shades and combinations of Colour. Those shades and combinations suggest those different tangible objects as at different distances, according to certain rules of Perspective, which it is, perhaps, not very easy to say how it is that we learn, whether by some particular instinct, or by some application of either reason or experience, which has become so perfectly habitual to us, that we are scarcely sensible when we make use of it.
The distinctness of this Perspective, the precision and accuracy with which, by means of it, we are capable of judging concerning the distance of different tangible objects, is greater or less, exactly in proportion as this distinctness, as this precision and accuracy are of more or less importance to us. We can judge of the distance of near objects, of the chairs and tables, for example, in the chamber where we are sitting, with the most perfect precision and accuracy; and if in broad day–light we ever stumble over any of them, it must be, not from any error in the Sight, but from some defect in the attention. The precision and accuracy of our judgment concerning such near objects are of the utmost importance to us, and constitute the great advantage which a man who sees has over one who is unfortunately blind. As the distance increases, the distinctness of this Perspective, the precision and accuracy of our judgment gradually diminish. Of the tangible objects which are even at the moderate distance of one, two, or three miles from the eye, we are frequently at a loss to determine which is nearest, and which remotest. It is seldom of much importance to us to judge with precision concerning the situation of the tangible objects which are even at this moderate distance. As the distance increases, our judgments become more and more uncertain; and at a very great distance, such as that of the fixed stars, it becomes altogether uncertain. The most precise knowledge of the relative situation of such objects could be of no other use to us than to satisfy the most unnecessary curiosity.
The distances at which different men can by Sight distinguish, with some degree of precision, the situation of the tangible objects which the visible ones represent, is very different; and this difference, though it, no doubt, may sometimes depend upon some difference in the original configuration of their eyes, yet seems frequently to arise altogether from the different customs and habits which their respective occupations have led them to contract. Men of letters, who live much in their closets, and have seldom occasion to look at very distant objects, are seldom far–sighted. Mariners, on the contrary, almost always are; those especially who have made many distant voyages, in which they have been the greater part of their time out of sight of land, and have in day–light been constantly looking out towards the horizon for the appearance of some ship, or of some distant shore. It often astonishes a land–man to observe with what precision a sailor can distinguish in the Offing, not only the appearance of a ship, which is altogether invisible to the land–man, but the number of her masts, the direction of her course, and the rate of her sailing. If she is a ship of his acquaintance, he frequently can tell her name, before the land–man has been able to discover even the appearance of a ship.
Visible objects, Colour, and all its different modifications, are in themselves mere shadows or pictures, which seem to float, as it were, before the organ of Sight. In themselves, and independent of their connection with the tangible objects which they represent, they are of no importance to us, and can essentially neither benefit us nor hurt us. Even while we see them we are seldom thinking of them. Even when we appear to be looking at them with the greatest earnestness, our whole attention is frequently employed, not upon them, but upon the tangible objects represented by them.
It is because almost our whole attention is employed, not upon the visible and representing, but upon the tangible and represented objects, that in our imaginations we are apt to ascribe to the former a degree of magnitude which does not belong to them, but which belongs altogether to the latter. If you shut one eye, and hold immediately before the other a small circle of plain glass, of not more than half an inch in diameter, you may see through that circle the most extensive prospects; lawns and woods, and arms of the sea, and distant mountains. You are apt to imagine that the Landscape which is thus presented to you, that the visible Picture which you thus see, is immensely great and extensive. The tangible objects which this visible Picture represents, undoubtedly are so. But the visible Picture which represents them can be no greater than the little visible circle through which you see it. If while you are looking through this circle, you could conceive a fairy hand and a fairy pencil to come between your eye and the glass, that pencil could delineate upon that little glass the outline of all those extensive lawns and woods, and arms of the sea, and distant mountains, in the full and exact dimensions with which they are really seen by the eye.19
Every visible object which covers from the eye any other visible object, must appear at least as large as that other visible object. It must occupy at least an equal portion of that visible plain or surface which is at that time presented to the eye. Opticians accordingly tell us, that all the visible objects which are seen under equal angles must to the eye appear equally large. But the visible object, which covers from the eye any other visible object, must necessarily be seen under angles at least equally large as those under which that other object is seen. When I hold up my finger, however, before my eye, it appears to cover the greater part of the visible chamber in which I am sitting. It should therefore appear as large as the greater part of that visible chamber. But because I know that the tangible finger bears but a very small proportion to the greater part of the tangible chamber, I am apt to fancy that the visible finger bears but a like proportion to the greater part of the visible chamber. My judgment corrects my eyesight, and, in my fancy, reduces the visible object, which represents the little tangible one, below its real visible dimensions; and, on the contrary, it augments the visible object which represents the great tangible one a good deal beyond those dimensions. My attention being generally altogether occupied about the tangible and represented, and not at all about the visible and representing objects, my careless fancy bestows upon the latter a proportion which does not in the least belong to them, but which belongs altogether to the former.
It is because the visible object which covers any other visible object must always appear at least as large as that other object, that Opticians tell us that the sphere of our vision appears to the eye always equally large; and that when we hold our hand before our eye in such a manner that we see nothing but the inside of the hand, we still see precisely the same number of visible points, the sphere of our vision is still as completely filled, the retina is as entirely covered with the object which is thus presented to it, as when we survey the most extensive horizon.
A young gentleman who was born with a cataract upon each of his eyes was, in one thousand seven hundred and twenty–eight, couched by Mr. Cheselden,20 and by that means for the first time made to see distinctly. ‘At first,’ says the operator, ‘he could bear but very little Sight, and the things he saw he thought extremely large; but upon seeing things larger, those first seen he conceived less, never being able to imagine any lines beyond the bounds he saw; the room he was in, he said, he knew to be but part of the house, yet he could not conceive that the whole house would look bigger.’21 It was unavoidable that he should at first conceive, that no visible object could be greater, could present to his eye a greater number of visible points, or could more completely fill the comprehension of that organ, than the narrowest sphere of his vision. And when that sphere came to be enlarged, he still could not conceive that the visible objects which it presented could be larger than those which he had first seen. He must probably by this time have been in some degree habituated to the connection between visible and tangible objects, and enabled to conceive that visible object to be small which represented a small tangible object; and that to be great, which represented a great one. The great objects did not appear to his Sight greater than the small ones had done before; but the small ones, which, having filled the whole sphere of his vision, had before appeared as large as possible, being now known to represent much smaller tangible objects, seemed in his conception to grow smaller. He had begun now to employ his attention more about the tangible and represented, than about the visible and representing objects; and he was beginning to ascribe to the latter, the proportions and dimensions which properly belonged altogether to the former.
As we frequently ascribe to the objects of Sight a magnitude and proportion which does not really belong to them, but to the objects of Touch which they represent, so we likewise ascribe to them a steadiness of appearance, which as little belongs to them, but which they derive altogether from their connection with the same objects of Touch. The chair which now stands at the farther end of the room, I am apt to imagine, appears to my eye as large as it did when it stood close by me, when it was seen under angles at least four times larger than those under which it is seen at present, and when it must have occupied, at least, sixteen times that portion which it occupies at present, of the visible plain or surface which is now before my eyes. But as I know that the magnitude of the tangible and represented chair, the principal object of my attention, is the same in both situations, I ascribe to the visible and representing chair (though now reduced to less than the sixteenth part of its former dimensions) a steadiness of appearance, which certainly belongs not in any respect to it, but altogether to the tangible and represented one. As we approach to, or retire from, the tangible object which any visible one represents, the visible object gradually augments in the one case, and diminishes in the other. To speak accurately, it is not the same visible object which we see at different distances, but a succession of visible objects, which, though they all resemble one another, those especially which follow near after one another; yet are all really different and distinct. But as we know that the tangible object which they represent remains always the same, we ascribe to them too a sameness which belongs altogether to it: and we fancy that we see the same tree at a mile, at half a mile, and at a few yards distance. At those different distances, however, the visible objects are so very widely different, that we are sensible of a change in their appearance. But still, as the tangible object which they represent remains invariably the same, we ascribe a sort of sameness even to them too.
It has been said, that no man ever saw the same visible object twice; and this, though, no doubt, an exaggeration, is, in reality, much less so than at first view it appears to be. Though I am apt to fancy that all the chairs and tables, and other little pieces of furniture in the room where I am sitting, appear to my eye always the same, yet their appearance is in reality continually varying, not only according to every variation in their situation and distance with regard to where I am sitting, but according to every, even the most insensible variation in the attitude22 of my body, in the movement of my head, or even in that of my eyes. The perspective necessarily varies according to all, even the smallest of these variations; and consequently the appearance of the objects which that perspective presents to me. Observe what difficulty a portrait painter finds, in getting the person who sits for his picture to present to him precisely that view of the countenance from which the first outline was drawn. The painter is scarce ever completely satisfied with the situation of the face which is presented to him, and finds that it is scarcely ever precisely the same with that from which he rapidly sketched the first outline. He endeavours, as well as he can, to correct the difference from memory, from fancy, and from a sort of art of approximation, by which he strives to express as nearly as he can, the ordinary effect of the look, air, and character of the person whose picture he is drawing. The person who draws from a statue, which is altogether immoveable, feels a difficulty, though, no doubt, in a less degree, of the same kind. It arises altogether from the difficulty which he finds in placing his own eye precisely in the same situation during the whole time which he employs in completing his drawing. This difficulty is more than doubled upon the painter who draws from a living subject. The statue never is the cause of any variation or unsteadiness in its own appearance. The living subject frequently is.
The benevolent purpose of nature in bestowing upon us the sense of seeing, is evidently to inform us concerning the situation and distance of the tangible objects which surround us. Upon the knowledge of this distance and situation depends the whole conduct of human life, in the most trifling as well as in the most important transactions. Even animal motion depends upon it; and without it we could neither move, nor even sit still, with complete security. The objects of sight, as Dr. Berkley finely observes,23 constitute a sort of language which the Author of Nature addresses to our eyes, and by which he informs us of many things, which it is of the utmost importance to us to know. As, in common language, the words or sounds bear no resemblance to the things which they denote, so, in this other language, the visible objects bear no sort of resemblance to the tangible object which they represent, and of whose relative situation, with regard both to ourselves and to one another, they inform us.
He acknowledges,24 however, that though scarcely any word be by nature better fitted to express one meaning than any other meaning, yet that certain visible objects are better fitted than others to represent certain tangible objects. A visible square, for example, is better fitted than a visible circle to represent a tangible square. There is, perhaps, strictly speaking, no such thing as either a visible cube, or a visible globe, the objects of sight being all naturally presented to the eye as upon one surface. But still there are certain combinations of colours which are fitted to represent to the eye, both the near and the distant, both the advancing and the receding lines, angles, and surfaces of the tangible cube; and there are others fitted to represent, in the same manner, both the near and the receding surface of the tangible globe. The combination which represents the tangible cube, would not be fit to represent the tangible globe; and that which represents the tangible globe, would not be fit to represent the tangible cube. Though there may, therefore, be no resemblance between visible and tangible objects, there seems to be some affinity or correspondence between them sufficient to make each visible object fitter to represent a certain precise tangible object than any other tangible object. But the greater part of words seem to have no sort of affinity or correspondence with the meanings or ideas which they express; and if custom had so ordered it, they might with equal propriety have been made use of to express any other meanings or ideas.
Dr. Berkley, with that happiness of illustration which scarcely ever deserts him, remarks,25 that this in reality is no more than what happens in common language; and that though letters bear no sort of resemblance to the words which they denote, yet that the same combination of letters which represents one word, would not always be fit to represent another; and that each word is always best represented by its own proper combination of letters. The comparison, however, it must be observed, is here totally changed. The connection between visible and tangible objects was first illustrated by comparing it with that between spoken language and the meanings or ideas which spoken language suggests to us; and it is now illustrated by the connection between written language and spoken language, which is altogether different. Even this second illustration, besides, will not apply perfectly to the case. When custom, indeed, has perfectly ascertained the powers of each letter; when it has ascertained, for example, that the first letter of the alphabet shall always represent such a sound, and the second letter such another sound; each word comes then to be more properly represented by one certain combination of written letters or characters, than it could be by any other combination. But still the characters themselves are altogether arbitrary, and have no sort of affinity or correspondence with the articulate sounds which they denote. The character which marks the first letter of the alphabet, for example, if custom had so ordered it, might, with perfect propriety, have been made use of to express the sound which we now annex to the second, and the character of the second to express that which we now annex to the first. But the visible characters which represent to our eyes the tangible globe, could not so well represent the tangible cube; nor could those which represent the tangible cube, so properly represent the tangible globe. There is evidently, therefore, a certain affinity and correspondence between each visible object and the precise tangible object represented by it, much superior to what takes place either between written and spoken language, or between spoken language and the ideas or meanings which it suggests. The language which nature addresses to our eyes, has evidently a fitness of representation, an aptitude for signifying the precise things which it denotes, much superior to that of any of the artificial languages which human art and ingenuity have ever been able to invent.
That this affinity and correspondence, however, between visible and tangible objects could not alone, and without the assistance of observation and experience, teach us, by any effort of reason, to infer what was the precise tangible object which each visible one represented, if it is not sufficiently evident from what has been already said, it must be completely so from the remarks of Mr. Cheselden upon the young gentleman above–mentioned, whom he had couched for a cataract. ‘Though we say of this gentleman, that he was blind,’ observes Mr. Cheselden, ‘as we do of all people who have ripe cataracts; yet they are never so blind from that cause but that they can discern day from night; and for the most part, in a strong light, distinguish black, white, and scarlet; but they cannot perceive the shape of any thing; for the light by which these perceptions are made, being let in obliquely through the aqueous humour, or the anterior surface of the crystalline, (by which the rays cannot be brought into a focus upon the retina,) they can discern in no other manner than a sound eye can through a glass of broken jelly, where a great variety of surfaces so differently refract the light, that the several distinct pencils of rays cannot be collected by the eye into their proper foci; wherefore the shape of an object in such a case cannot be at all discerned, though the colour may: and thus it was with this young gentleman, who, though he knew those colours asunder in a good light, yet when he saw them after he was couched, the faint ideas he had of them before were not sufficient for him to know them by afterwards; and therefore he did not think them the same which he had before known by those names.’26 This young gentleman, therefore, had some advantage over one who from a state of total blindness had been made for the first time to see. He had some imperfect notion of the distinction of colours; and he must have known that those colours had some sort of connection with the tangible objects which he had been accustomed to feel. But had he emerged from total blindness, he could have learnt this connection only from a very long course of observation and experience. How little this advantage availed him, however, we may learn partly from the passages of Mr. Cheselden’s narrative, already quoted, and still more from the following:
‘When he first saw,’ says that ingenious operator, ‘he was so far from making any judgment about distances, that he thought all objects whatever touched his eyes (as he expressed it) as what he felt did his skin; and thought no objects so agreeable as those which were smooth and regular, though he could form no judgment of their shape, or guess what it was in any object that was pleasing to him. He knew not the shape of any thing, nor any one thing from another, however different in shape or magnitude; but upon being told what things were, whose form he before knew from feeling, he would carefully observe, that he might know them again; but having too many objects to learn at once, he forgot many of them; and (as he said) at first learned to know, and again forgot a thousand things in a day. One particular only (though it may appear trifling) I will relate: Having often forgot which was the cat, and which the dog, he was ashamed to ask; but catching the cat (which he knew by feeling) he was observed to look at her stedfastly, and then setting her down, said, So, puss! I shall know you another time.’27
When the young gentleman said, that the objects which he saw touched his eyes, he certainly could not mean that they pressed upon or resisted his eyes; for the objects of sight never act upon the organ in any way that resembles pressure or resistance. He could mean no more than that they were close upon his eyes, or, to speak more properly, perhaps, that they were in his eyes. A deaf man, who was made all at once to hear, might in the same manner naturally enough say, that the sounds which he heard touched his ears, meaning that he felt them as close upon his ears, or, to speak, perhaps, more properly, as in his ears.
Mr. Cheselden adds afterwards: ‘We thought he soon knew what pictures represented which were shewed to him, but we found afterwards we were mistaken; for about two months after he was couched, he discovered at once they represented solid bodies, when, to that time, he considered them only as party–coloured planes, or surfaces diversified with variety of paints; but even then he was no less surprised, expecting the pictures would feel like the things they represented, and was amazed when he found those parts, which by their light and shadow appeared now round and uneven, felt only flat like the rest; and asked which was the lying sense, feeling or seeing?’28
Painting, though, by combinations of light and shade, similar to those which Nature makes use of in the visible objects which she presents to our eyes, it endeavours to imitate those objects; yet it never has been able to equal the perspective of Nature, or to give to its productions that force and distinctness of relief and projection which Nature bestows upon hers. When the young gentleman was just beginning to understand the strong and distinct perspective of Nature, the faint and feeble perspective of Painting made no impression upon him, and the picture appeared to him what it really was, a plain surface bedaubed with different colours. When he became more familiar with the perspective of Nature, the inferiority of that of Painting did not hinder him from discovering its resemblance to that of Nature. In the perspective of Nature, he had always found that the situation and distance of the tangible and represented objects, corresponded exactly to what the visible and representing ones suggested to him. He expected to find the same thing in the similar, though inferior perspective of Painting, and was disappointed when he found that the visible and tangible objects had not, in this case, their usual correspondence.
‘In a year after seeing,’ adds Mr. Cheselden, ‘the young gentleman being carried upon Epsom–downs, and observing a large prospect, he was exceedingly delighted with it, and called it a new kind of seeing.’29 He had now, it is evident, come to understand completely the language of Vision. The visible objects which this noble prospect presented to him did not now appear as touching, or as close upon his eye. They did not now appear of the same magnitude with those small objects to which, for some time after the operation, he had been accustomed, in the little chamber where he was confined. Those new visible objects at once, and as it were of their own accord, assumed both the distance and the magnitude of the great tangible objects which they represented. He had now, therefore, it would seem, become completely master of the language of Vision, and he had become so in the course of a year; a much shorter period than that in which any person, arrived at the age of manhood, could completely acquire any foreign language. It would appear too, that he had made very considerable progress even in the two first months. He began at that early period to understand even the feeble perspective of Painting; and though at first he could not distinguish it from the strong perspective of Nature, yet he could not have been thus imposed upon by so imperfect an imitation, if the great principles of Vision had not beforehand been deeply impressed upon his mind, and if he had not, either by the association of ideas, or by some other unknown principle, been strongly determined to expect certain tangible objects in consequence of the visible ones which had been presented to him. This rapid progress, however, may, perhaps, be accounted for from that fitness of representation, which has already been taken notice of, between visible and tangible objects. In this language of Nature, it may be said, the analogies are more perfect; the etymologies, the declensions, and conjugations, if one may say so, are more regular than those of any human language. The rules are fewer, and those rules admit of no exceptions.
But though it may have been altogether by the slow paces of observation and experience that this young gentleman acquired the knowledge of the connection between visible and tangible objects; we cannot from thence with certainty infer, that young children have not some instinctive perception of the same kind. In him this instinctive power, not having been exerted at the proper season, may, from disuse, have gone gradually to decay, and at last have been completely obliterated. Or, perhaps, (what seems likewise very possible,) some feeble and unobserved remains of it may have somewhat facilitated his acquisition of what he might otherwise have found it much more difficult to acquire.
That, antecedent to all experience, the young of at least the greater part of animals possess some instinctive perception of this kind, seems abundantly evident. The hen never feeds her young by dropping the food into their bills, as the linnet and the thrush feed theirs. Almost as soon as her chickens are hatched, she does not feed them, but carries them to the field to feed, where they walk about at their ease, it would seem, and appear to have the most distinct perception of all the tangible objects which surround them. We may often see them, accordingly, by the straightest road, run to and pick up any little grains which she shews them, even at the distance of several yards; and they no sooner come into the light than they seem to understand this language of Vision as well as they ever do afterwards. The young of the partridge and of the grouse seem to have, at the same early period, the most distinct perceptions of the same kind. The young partridge, almost as soon it comes from the shell, runs about among long grass and corn; the young grouse among long heath, and would both most essentially hurt themselves if they had not the most acute, as well as distinct perception of the tangible objects which not only surround them but press upon them on all sides. This is the case too with the young of the goose, of the duck, and, so far as I have been able to observe,30 with those of at least the greater part of the birds which make their nests upon the ground, with the greater part of those which are ranked by Linnaeus in the orders of the hen and the goose, and of many of those long–shanked and wading birds which he places in the order that he distinguishes by the name of Grallae.31
The young of those birds that build their nests in bushes, upon trees, in the holes and crevices of high walls, upon high rocks and precipices, and other places of difficult access; of the greater part of those ranked by Linnaeus in the orders of the hawk, the magpie, and the sparrow, seem to come blind from the shell, and to continue so for at least some days thereafter. Till they are able to fly they are fed by the joint labour of both parents. As soon as that period arrives, however, and probably for some time before, they evidently enjoy all the powers of Vision in the most complete perfection, and can distinguish with most exact precision the shape and proportion of the tangible objects which every visible one represents. In so short a period they cannot be supposed to have acquired those powers from experience, and must therefore derive them from some instinctive suggestion. The sight of birds seems to be both more prompt and more acute than that of any other animals. Without hurting themselves they dart into the thickest and most thorny bushes, fly with the utmost rapidity through the most intricate forests, and while they are soaring aloft in the air, discover upon the ground the little insects and grains upon which they feed.
The young of several sorts of quadrupeds seem, like those of the greater part of birds which make their nests upon the ground, to enjoy as soon as they come into the world the faculty of seeing as completely as they ever do afterwards. The day, or the day after they are dropt, the calf follows the cow, and the foal the mare, to the field; and though from timidity they seldom remove far from the mother, yet they seem to walk about at their ease; which they could not do unless they could distinguish, with some degree of precision, the shape and proportion of the tangible objects which each visible one represents. The degree of precision, however, with which the horse is capable of making this distinction, seems at no period of his life to be very complete. He is at all times apt to startle at many visible objects, which, if they distinctly suggested to him the real shape and proportion of the tangible objects which they represent, could not be the objects of fear; at the trunk or root of an old tree, for example, which happens to be laid by the road side, at a great stone, or the fragment of a rock which happens to lie near the way where he is going. To reconcile him, even to a single object of this kind, which has once alarmed him, frequently requires some skill, as well as much patience and good temper, in the rider. Such powers of sight, however, as Nature has thought proper to render him capable of acquiring, he seems to enjoy from the beginning, in as great perfection as he ever does afterwards.
The young of other quadrupeds, like those of the birds which make their nests in places of difficult access, come blind into the world. Their sight, however, soon opens, and as soon as it does so,32 they seem to enjoy it in the most complete perfection, as we may all observe in the puppy and the kitten. The same thing, I believe, may be said of all other beasts of prey, at least of all those concerning which I have been able to collect any distinct information. They come blind into the world; but as soon as their sight opens, they appear to enjoy it in the most complete perfection.
It seems difficult to suppose that man is the only animal of which the young are not endowed with some instinctive perception of this kind. The young of the human species, however, continue so long in a state of entire dependency, they must be so long carried about in the arms of their mothers or of their nurses, that such an instinctive perception may seem less necessary to them than to any other race of animals. Before it could be of any use to them, observation and experience may, by the known principle of the association of ideas, have sufficiently connected in their young minds each visible object with the corresponding tangible one which it is fitted to represent. Nature, it may be said, never bestows upon any animal any faculty which is not either necessary or useful, and an instinct of this kind would be altogether useless to an animal which must necessarily acquire the knowledge which the instinct is given to supply, long before that instinct could be of any use to it. Children, however, appear at so very early a period to know the distance, the shape, and magnitude of the different tangible objects which are presented to them, that I am disposed to believe that even they may have some instinctive perception of this kind; though possibly in a much weaker degree than the greater part of other animals. A child that is scarcely a month old, stretches out its hands to feel any little play–thing that is presented to it. It distinguishes its nurse, and the other people who are much about it, from strangers. It clings to the former, and turns away from the latter. Hold a small looking–glass before a child of not more than two or three months old, and it will stretch out its little arms behind the glass, in order to feel the child which it sees, and which it imagines is at the back of the glass. It is deceived, no doubt; but even this sort of deception sufficiently demonstrates that it has a tolerably distinct apprehension of the ordinary perspective of Vision, which it cannot well have learnt from observation and experience.
Do any of our other senses, antecedently to such observation and experience, instinctively suggest to us some conception of the solid and resisting substances which excite their respective sensations; though these sensations bear no sort of resemblance to those substances?
The sense of Tasting certainly does not. Before we can feel the sensation, the solid and resisting substance which excites it must be pressed against the organs of Taste, and must consequently be perceived by them. Antecedently to observation and experience, therefore, the sense of Tasting can never be said instinctively to suggest some conception of that substance.
It may, perhaps, be otherwise with the sense of Smelling. The young of all suckling animals, (of the Mammalia of Linnaeus,) whether they are born with sight or without it, yet as soon as they come into the world apply to the nipple of the mother in order to suck. In doing this they are evidently directed by the Smell. The Smell appears either to excite the appetite for the proper food, or at least to direct the new–born animal to the place where that food is to be found. It may perhaps do both the one and the other.
That when the stomach is empty, the Smell of agreeable food excites and irritates the appetite, is what we all must have frequently experienced. But the stomach of every new–born animal is necessarily empty. While in the womb it is nourished, not by the mouth, but by the navel–string. Children have been born apparently in the most perfect health and vigour, and have applied to suck in the usual manner; but immediately, or soon after, have thrown up the milk, and in the course of a few hours have died vomiting and in convulsions. Upon opening their bodies it has been found that the intestinal tube or canal had never been opened or pierced in the whole extent of its length; but, like a sack, admitted of no passage beyond a particular place. It could not have been in any respect by the mouth, therefore, but altogether by the navel–string, that such children had been nourished and fed up to the degree of health and vigour in which they were born. Every animal, while in the womb, seems to draw its nourishment, more like a vegetable, from the root, than like an animal from the mouth; and that nourishment seems to be conveyed to all the different parts of the body by tubes and canals in many respects different from those which afterwards perform the same function. As soon as it comes into the world, this new set of tubes and canals, which the providential care of Nature had for a long time before been gradually preparing, is all at once and instantaneously opened. They are all empty, and they require to be filled. An uneasy sensation accompanies the one situation, and an agreeable one the other. The smell of the substance which is fitted for filling them, increases and irritates that uneasy sensation, and produces hunger, or the appetite for food.
But all the appetites which take their origin from a certain state of the body, seem to suggest the means of their own gratification; and, even long before experience, some anticipation or preconception of the pleasure which attends that gratification. In the appetite for sex, which frequently, I am disposed to believe almost always, comes a long time before the age of puberty,33 this is perfectly and distinctly evident. The appetite for food suggests to the new–born infant the operation of sucking, the only means by which it can possibly gratify that appetite. It is continually sucking. It sucks whatever is presented to its mouth. It sucks even when there is nothing presented to its mouth, and some anticipation or preconception of the pleasure which it is to enjoy in sucking, seems to make it delight in putting its mouth in the shape and configuration by which it alone can enjoy that pleasure. There are other appetites in which the most unexperienced imagination produces a similar effect upon the organs which Nature has provided for their gratification.
The Smell not only excites the appetite, but directs to the object which can alone gratify that appetite. But by suggesting the direction towards that object, the Smell must necessarily suggest some notion of distance and externality, which are necessarily involved in the idea of direction; in the idea of the line of motion by which the distance can best be overcome, and the mouth brought into contact with the unknown substance which is the object of the appetite. That the Smell should alone suggest any preconception of the shape or magnitude of the external body to which it directs, seems not very probable. The sensation of Smell seems to have no sort of affinity or correspondence with shape or magnitude; and whatever preconception the infant may have of these, (and it may very probably have some such preconception,) is likely to be suggested, not so much directly by the Smell, and indirectly by the appetite excited by that Smell; as by the principle which teaches the child to mould its mouth into the conformation and action of sucking, even before it reaches the object to which alone that conformation and action can be usefully applied.
The Smell, however, as it suggests the direction by which the external body must be approached, must suggest at least some vague idea or preconception of the existence of that body; of the thing to which it directs, though not perhaps of the precise shape and magnitude of that thing. The infant, too, feeling its mouth attracted and drawn as it were towards that external body, must conceive the Smell which thus draws and attracts it, as something belonging to or proceeding from that body, or what is afterwards denominated and obscurely understood to be as a sort of quality or attribute of that body.
The Smell, too, may very probably suggest some even tolerably distinct perception of the Taste of the food to which it directs. The respective objects of our different external senses seem, indeed, the greater part of them, to bear no sort of resemblance to one another. Colour bears no sort of resemblance to Solidity, nor to Heat, nor to Cold, nor to Sound, nor to Smell, nor to Taste. To this general rule, however, there seems to be one, and perhaps but one exception. The sensations of Smell and Taste seem evidently to bear some sort of resemblance to one another. Smell appears to have been given to us by Nature as the director of Taste. It announces, as it were, before trial, what is likely to be the Taste of the food which is set before us. Though perceived by a different organ, it seems in many cases to be but a weaker sensation nearly of the same kind with that of the Taste which that announces. It is very natural to suppose, therefore, that the Smell may suggest to the infant some tolerably distinct preconception of the Taste of the food which it announces, and may, even before experience, make its mouth, as we say, water for that food.
That numerous division of animals which Linnaeus ranks under the class of worms, have, scarcely any of them, any head. They neither see nor hear, have neither eyes nor ears; but many of them have the power of self–motion, and appear to move about in search of their food. They can be directed in this search by no other sense than that of Smelling. The most accurate microscopical observations, however, have never been able to discover in such animals any distinct organ of Smell. They have a mouth and a stomach, but no nostrils. The organ of Taste, it is probable, has in them a sensibility of the same kind with that which the olfactory nerves have in more perfect animals. They may, as it were, taste at a distance, and be attracted to their food by an affection of the same organ by which they afterwards enjoy it; and Smell and Taste may in them be no otherwise distinguished than as weaker or stronger sensations derived from the same organ.
The sensations of Heat and Cold, when excited by the pressure of some body either heated or cooled beyond the actual temperature of our own organs, cannot be said, antecedently to observation and experience, instinctively to suggest any conception of the solid and resisting substance which excites them. What was said of the sense of Taste may very properly be said here. Before we can feel those sensations, the pressure of the external body which excites them must necessarily suggest, not only some conception, but the most distinct conviction of its own external and independent existence.
It may be otherwise, perhaps, when those sensations are either of them excited by the temperature of the external air. In a calm day when there is no wind, we scarcely perceive the external air as a solid body; and the sensations of Heat and Cold, it may be thought, are then felt merely as affections of our own body, without any reference to any thing external. Several cases, however, may be conceived, in which it must be allowed, I imagine, that those sensations, even when excited in this manner, must suggest some vague notion of some external thing or substance which excites them. A new–born animal, which had the power of self–motion, and which felt its body, either agreeably or disagreeably, more heated or more cooled on the one side than on the other, would, I imagine, instinctively, and antecedently to all observation and experience, endeavour to move towards the side in which it felt the agreeable, and to withdraw from that in which it felt the disagreeable sensation. But the very desire of motion supposes some notion or preconception of externality; and the desire to move towards the side of the agreeable, or from that of the disagreeable sensation, supposes at least some vague notion of some external thing or place which is the cause of those respective sensations.
The degrees of Heat and Cold which are agreeable, it has been found from experience, are likewise healthful; and those which are disagreeable, unwholesome. The degree of their unwholesomeness, too, seems to be pretty much in proportion to that of their disagreeableness. If either of them is so disagreeable as to be painful, it is generally destructive; and that, too, in a very short period of time. Those sensations appear to have been given us for the preservation of our own bodies. They necessarily excite the desire of changing our situation when it is unwholesome or destructive; and when it is healthy, they allow us, or rather they entice us, to remain in it. But the desire of changing our situation necessarily supposes some idea of externality; or of motion into a place different from that in which we actually are; and even the desire of remaining in the same place supposes some idea of at least the possibility of changing. Those sensations could not well have answered the intention of Nature, had they not thus instinctively suggested some vague notion of external existence.
That Sound, the object of the sense of Hearing, though perceived itself as in the ear, and nowhere but in the ear, may likewise, instinctively, and antecedently to all observation and experience, obscurely suggest some vague notion of some external substance or thing which excites it, I am much disposed to believe.34 I acknowledge, however, that I have not been able to recollect any one instance in which this sense seems so distinctly to produce this effect, as that of Seeing, that of Smelling, and even that of Heat and Cold, appear to do in some particular cases. Unusual and unexpected Sound alarms always, and disposes us to look about for some external substance or thing as the cause which excites it, or from which it proceeds. Sound, however, considered merely as a sensation, or as an affection of the organ of Hearing, can in most cases neither benefit nor hurt us. It may be agreeable or disagreeable, but in its own nature it does not seem to announce any thing beyond the immediate feeling. It should not therefore excite any alarm. Alarm is always the fear of some uncertain evil beyond what is immediately felt, and from some unknown and external cause. But all animals, and men among the rest, feel some degree of this alarm, start, are roused and rendered circumspect and attentive by unusual and unexpected Sound. This effect, too, is produced so readily and so instantaneously that it bears every mark of an instinctive suggestion of an impression immediately struck by the hand of Nature, which does not wait for any recollection of past observation and experience. The hare, and all those other timid animals to whom flight is the only defence, are supposed to possess the sense of Hearing in the highest degree of activeness. It seems to be the sense in which cowards are very likely to excel.35
The three senses of Seeing, Hearing, and Smelling, seem to be given to us by Nature, not so much in order to inform us concerning the actual situation of our bodies, as concerning that of those other external bodies, which, though at some distance from us, may sooner or later affect that actual situation, and eventually either benefit or hurt us.
[1 ]Explicitly only in the later Principles of Human Knowledge that Smith may not have seen.
[2 ]J. R. Lindgren, ‘Adam Smith’s Theory of Inquiry’, Journal of Political Economy, lxxvii (1969).
[1 ]Cf. Locke, Essay concerning Human Understanding, especially II.iv.3.
[2 ][Cf. Astronomy, IV.38.]
[3 ]This surmise as to the absence of any ‘privileged’ body in the universe is of course connected with the question of the relativity of all motion; cf. Leibniz–Clarke Correspondence (ed. H. G. Alexander, 1956) and Berkeley, Principles of Human Knowledge, § 113.
[4 ]Presumably Descartes and his followers.
[5 ][Aristotle, Physics, IV.6, 213a27; De Caelo, II.13, 294b21–3. Lucretius, De Rerum Natura, i.269 ff.]
[6 ]Smith’s cautious comment shows remarkable sagacity. Though probably the majority of the contemporary ‘philosophers’ adopted what they took to be Newton’s ‘material corpuscular’ hypothesis rather than the somewhat loosely–named ‘wave theory’ mainly associated with Hooke and Huygens, the choice is now recognized to be far from simple. Newton himself with his customary caution set out his views in the form of Queries appended to the later editions of his Opticks. Though he regarded ‘all hypotheses as erroneous in which light is supposed to consist in pression or motion propagated through a fluid medium’ (Q.28), nevertheless he had to have recourse to a subsidiary hypothesis of waves in an ‘etherial’ medium acting on the light rays to account for certain anomalous forms of behaviour in the latter. Finally—very relevant to Smith’s comment—he asked ‘Are not gross bodies and light convertible into one another?’ (Q.30). The issue was apparently resolved in favour of transverse vibrations of an ‘ether’ by Thomas Young a few years after Smith’s death. Once again discrepancies appeared which only the advent of the Quantum Theory was able to resolve—if that is the word!
[7 ]i.e. the Accademia del Cimento in Florence. See Essayes of Natural Experiments made in the Academie del Cimento, the English translation of their Saggi, by Richard Waller (1648), 204. That views opposed to atomism are not in themselves to be so hastily dismissed was proved in 1758, when there appeared Roger Boscovich’s Philosophiae Naturalis Theoria, a work in which ‘atoms’ were entirely replaced by ‘forces’, and which exerted a notable influence on Davy, Faraday, Lord Kelvin, and Maxwell.
[8 ][Notably in Syntagma Philosophicum, Part II.]
[9 ]Smith was of course right to separate sensations of heat, etc., from those of touch: separate nervous receptors were later demonstrated.
[10 ]This is certainly true only in respect of strong odours.
[11 ]An example of ‘psychologism’. As a statement of fact it is just plain false. Sensation and inference are reversed. See also §§ 65, 77, below.
[12 ]But apparently this does not apply to gravity. See the editor’s Introduction, 21–2.
[13 ]Principia, Book II, Section 8. Newton’s result was of the right order only. By assuming volume changes to be at constant temperature (isothermal) instead of at constant heat–content (adiabatic), he failed to apply the appropriate law. This was corrected by Laplace in Annales de Chimie et de Physique, iii (1816), 20.
[14 ][Benjamin Franklin, Experiments and Observations on Electricity, made at Philadelphia (1751).]
[15 ]Smith uses this spelling throughout. The Essay towards a New Theory of Vision appeared in 1709, the Principles of Human Knowledge in 1710. Smith seems to take no account of the radical ‘immaterialism’ of the latter; there is no evidence that he ever read it. [Smith did, however, own a copy of Berkeley’s Works.]
[16 ]Confusion between ‘seeing’ (which we are said to ‘imagine’—an ambiguous word still productive of more fundamental confusions—see the editor’s Introduction, 14–15) and the inference from analysis. Cf. § 53 below, ‘seem to float’.
[17 ][Human Understanding, III.iv.11.]
[18 ][New Theory of Vision, § 131.]
[19 ][Cf. TMS III.3.2, where Smith compares the role of imagination in perception and in moral judgement: ‘In my present situation an immense landscape of lawns, and woods, and distant mountains, seems to do no more than cover the little window which I write by’. (In the first printing of the Glasgow edition of TMS, 135, the word ‘mountains’ is incorrectly given as ‘mountain’.) Smith goes on to say that a man must know something of ‘the philosophy of vision’ to appreciate these matters. It seems probable that the TMS passage recalls the present one rather than vice versa, and this tends to confirm the hypothesis (editor’s Introduction, 133) of an early date for the composition of this essay.]
[20 ]William Cheselden (or Chesselden) (1688–1752), the most distinguished British surgeon before John Hunter. This famous case–history effectually answered the question put to Locke by William Molyneux (1656–98) after he had read the first edition of Locke’s Human Understanding, viz. could a person born blind, whose sight was subsequently restored, be able, by sight alone, to distinguish and identify objects already familiar to him by touch? For a full discussion see A. D. Ritchie, George Berkeley, a Reappraisal (ed. G. E. Davie, 1967), 13–18.
[21 ][Op. cit., 449. Here, as in the remainder of the quotations from this source, Smith has ‘modernized’ the spelling and punctuation.]
[22 ][The text of the original edition has ‘altitude’, presumably a printer’s error.]
[23 ][New Theory of Vision, § 147.] The paragraphs that follow in Smith’s essay are perhaps the most important for the further consideration of his views on language and his general approach to the nature of ‘philosophical investigation’. [Smith’s ‘Considerations Concerning the First Formation of Languages’ was first published in 1761. The subject is also considered in LRBL, lecture 3.]
[24 ][§§ 142, 152.]
[25 ][Smith is referring to New Theory of Vision, § 143, but does not bring out Berkeley’s point clearly enough. Berkeley’s argument is that visible figures represent tangible figures as written words represent sounds: it is arbitrary that written letters should represent sounds, but if letters are used for that purpose, the particular combination of letters in a written word must have a certain correlation with the elements of the sound represented. Smith’s criticism is not impaired by his compression of Berkeley’s argument.]
[26 ][‘Account of Observations’, 447–8. The original has ‘the gentleman’, not ‘this gentleman’, at the beginning of the quotation, and ‘these colours’, not ‘those colours’, later.]
[28 ][449. The original has ‘paint’, not ‘paints’.]
[29 ][‘Account of Observations’, 450. The original reads: ‘A year after first seeing, being carried upon Epsom–downs . . .’]
[30 ]The record of these comparative field studies casts an important light on the nature of Smith’s method.
[31 ][In his Systema Naturae.]
[32 ]This may be questioned; degree of mobility may be relevant.
[33 ]A remarkable anticipation of Freud’s claim, received by his contemporaries with scepticism, if not categorical denial.
[34 ]Though based on a dubious premiss, Smith’s point is well taken in regard to the general question of the sensory origin of knowledge.
[35 ]Smith seems to have had an obsession about ‘cowards’ (cf. Astronomy, III.1). ‘Hunters’ might be similarly endowed.