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 1
Senses, 43). Unfortunately, he does not seem to realize that Berkeley’s analysis had vitiated 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 http://oll.libertyfund.org/Texts/LFBooks/Smith0232/GlasgowEdition/PhilosophicalSubjects...
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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 2
to linguistic origin and structure a major factor in Smith’s whole methodology.
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; 1
Seeing, Hearing, Smelling, Tasting, and Touching.
Of these, the four first mentioned are each of them confined to particular parts or organs of the 2
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 of TOUCHING
THE objects of Touch always present themselves as pressing upon, or as resisting the particular 3
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.
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In moving my hand along the table it soon comes, in every direction, to a place where this 4
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 5
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 6
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 7
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 8
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 9
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 1
cannot even conceive how they should be capable of pressure or resistance; 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 10
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.
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Every solid and extended body, if it be not infinite, (as the universe may be conceived to be,) 11
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 12
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 2
imagination, supposed to be more fitted for rest than for motion. 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 3
perfectly at rest, with regard to all other surrounding bodies.
These four qualities, or attributes of extension, divisibility, figure, and mobility, or the capacity of 13
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 4
most indubitable certainty, by philosophers of very eminent reputation.
Of these external and resisting substances, some yield easily, and change their figure, at least in 14
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 15
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 5
from Aristotle and Lucretius, 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 http://oll.libertyfund.org/Texts/LFBooks/Smith0232/GlasgowEdition/PhilosophicalSubjects...
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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 6
accordingly doubt, and some even deny, that light is a material or corporeal substance.
Though all bodies or solid substances resist, yet all those with which we are acquainted appear to 16
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 7
occupy. An experiment of the Florentine academy 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 17
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 18
8
revived by Gassendi, 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 http://oll.libertyfund.org/Texts/LFBooks/Smith0232/GlasgowEdition/PhilosophicalSubjects...
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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 19
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 20
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 9
in our hand, or in the principle of perception which feels in our hand.
But though the sensations of heat and cold do not necessarily suggest the presence of any 21
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 http://oll.libertyfund.org/Texts/LFBooks/Smith0232/GlasgowEdition/PhilosophicalSubjects...
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obvious judgments of mankind, but which in reality is perfectly agreeable to those judgments.
Of the Sense of TASTING
WHEN we taste any solid or liquid substance, we have always two distinct perceptions; first, that 22
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 of SMELLING
10
EVERY smell or odour is naturally felt as in the nostrils;
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 of HEARING
11
EVERY sound is naturally felt as in the Ear, the organ of Hearing.
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 http://oll.libertyfund.org/Texts/LFBooks/Smith0232/GlasgowEdition/PhilosophicalSubjects...
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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 25
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 26
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 27
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 28
which excite them, though the s