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essay ii: External Senses - Henry Home, Lord Kames, Essays on the Principles of Morality and Natural Religion 
Essays on the Principles of Morality and Natural Religion, Corrected and Improved, in a Third Edition. Several Essays Added Concerning the Proof of a Deity, Edited and with an Introduction by Mary Catherine Moran (Indianapolis: Liberty Fund, 2005).
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An internal sense informs us of things passing within the mind, inclining, resolving, willing, reflecting, &c. By several external senses we discover things external. The latter is our present theme, as far as may tend to enforce the proof of a Deity.
For the sake of perspicuity, this Essay is divided into several sections. First, perceptions of the different external senses. Second, substance and qualities. Third, primary and secondary qualities. Fourth, veracity of the external senses.i
Perceptions of External Senseii
The perceptions of the external senses differ widely one from another. I begin with the perceptions of touch and sight as the simplest. I close my eyes and lay a hand on my writing desk. I feel my hand resisted by a hard smooth body, of a certain figure. Viewing the same desk with my eyes, the figure appears the same, as far as the perceptions of these two senses correspond. But it is more material to be observed, that by each of these senses I am informed, that the desk exists independent of me, having certain properties or qualities equally independent. These senses serve evidently to inform me of things as they really exist.
The senses of hearing, smelling, and tasting, raise perceptions differing widely from these mentioned. A sound is produced in me by a certain vibration of the air striking the drum of my ear: a smell, by effluvia touching my nostrils: and a taste by a bit of matter touching my palate. With respect to these senses, it is not a little remarkable, that their perceptions have no resemblance to the causes that produced them; nor do they correspond to any thing existing independent of me. The beat of a drum produces nothing but a vibrating motion in the air; nor does any thing touch my ear but that vibration. The effect however is a perception of sound, which has not the slightest affinity either to the beat of the drum or vibration of the air; nor has it any existence but in my mind. A rose emits effluvia which touch my nostrils: the smell I perceive is neither in the rose nor in the effluvia. The sweetness I taste in sugar, is produced by the sugar; but in vain would one search for that quality in the sugar, more than in any other bit of matter. From this analysis it appears, that a sound, a smell, a taste, are not matter nor qualities of matter; but effects produced in a percipient. No mortal would without experience imagine, that such marvelous effects could be produced by causes in all appearance so inadequate, effects however that contribute in a high degree to our well-being.
Substance and Quality
As a just conception of the terms substance and quality is necessary in many branches of reasoning, particularly in reasoning about a Deity, and as the explanation given of these terms by Mr. Locke, our great master in logic, is extremely obscure, I shall endeavour to ascertain their meaning, to the satisfaction, I expect, of my reader.1
I cast my eye upon a tree, and perceive figure, extension, colour, and sometimes motion. Were these perceived as separate objects without relation to any other thing, I should never have any idea of substance. This possibly may be the condition of some animals; but the eye of man is more perfect. What we really perceive, is a tree of a certain figure, size, and colour. When I see motion, my perception is not of motion separately, but of a body moving. And so closely are these united, that we cannot even form a conception of motion, nor of colour, nor of figure, as independent existences, but as belonging to the tree and inhering in it. In short, the sense of seeing is given us to perceive things as they really exist; and did it not make us acquainted with things as they exist, we would be ill qualified for living in this world. Now, when we abstract from particulars, and reason in general, the things that have not a separate existence are termed qualities, and the thing they belong to, body or substance. Thus the idea of substance, as well as of qualities, is derived from sight. And the object so qualified, is at the same time perceived as really existing, independent altogether of the percipient.
A similar perception arises from the sense of feeling. Laying my hand upon this table, I have a perception not only of smoothness, hardness, figure, and extension, but also of a thing I call body, of which the particulars now mentioned are perceived as qualities. Smoothness, hardness, extension, and figure, are perceived, not as separate and unconnected existences, but as inhering in and belonging to something I call body, which is really existing, and which hath an independent and permanent existence. And it is this body with its several qualities, which I express by the word table.
The foregoing analysis of the perceptions of sight and touch, will be best illustrated by a comparison with the perceptions of the other senses. I hear a sound, or I feel a smell. These are not perceived as the qualities or properties of any body, thing, or substance. They make their appearance in the mind as simple existences; and do not suggest any perception of independency, nor permanent existence. Did seeing and feeling carry us no farther, we never could have the least conception of substance.
It is not a little surprising, that philosophers, who discourse so currently of qualities, should affect so much doubt and hesitation about substance; seeing these are relative ideas, and imply each other. For what other reason do we call figure a quality, but that we perceive it, not as a separate existence, but as belonging to something that is figured; and which thing we call sub-stance, because it is not a property of any other thing, but is a thing which subsists by itself, or hath an independent existence. Did we perceive figure as we perceive sound, it would not be considered as a quality. In a word, a quality is not intelligible, unless upon supposition of some other thing, of which it is the quality. Sounds indeed, and smells, are also considered as qualities. But this proceeds from habit, not from original perception. For, having once acquired the distinction betwixt a thing and its qualities, and finding sound and smell more to resemble qualities than substances, we readily come into the use of considering them as qualities.
Another observation hinted above occurs, with regard to those things which by the sight and touch are perceived as qualities; that we cannot form a conception of them, independent of the beings to which they belong. It is not in our power to separate, even in imagination, colour, figure, motion, and extension, from body or substance. There is no such thing as conceiving motion by itself, abstracted from some body which is in motion. Let us try ever so often, our attempts will be in vain, to form an idea of a triangle independent of a body which has that figure. We cannot conceive a body that is not figured; and we can as little conceive a figure without a body; for this would be to conceive a figure as having a separate existence, at the same time that we conceive it as having no separate existence; or to conceive it to be a quality, and not a quality. Thus it comes out, that substance makes a part, not only of every perception of sight and touch, but of every conception we can form of colour, figure, extension, and motion. Taking in the whole train of our ideas, there is not one more familiar to us, than that of substance, a being or thing which hath qualities.
When these things are considered, I cannot readily discover what wrong conception of the matter hath led Mr. Locke to talk so obscurely and indistinctly of the idea of substance. It is no wonder he should be difficulted to form an idea of substance in general, abstracted from all properties, when such abstraction is beyond our power: but nothing is more easy, than to form an idea of any particular substance with its properties. Yet this has some how escaped him. When he forms the idea of a horse or a stone, he admits nothing into the idea, but a collection of several simple ideas of sensible qualities.* “And because,” says he,
we cannot conceive how these qualities should subsist alone, nor one in another, we suppose them existing in and supported by some common subject, which support we denote by the name substance; though it be certain we have no clear or distinct idea of that thing we suppose a support.
A single question would have unfolded the whole mystery. How comes it, that we cannot conceive qualities to subsist alone, nor one in another? Mr. Locke himself must have given the following answer, That the thing is not conceivable; because a property or quality cannot subsist without the thing to which it belongs; for if it did, that it would cease to be a property or quality. Why then does he make so faint an inference, as that we suppose qualities existing in and supported by some common subject? It is not a bare supposition: it is an essential part of the idea; it is necessarily suggested to us by sight and touch. He observes, that we have no clear nor distinct idea of substance. If he mean, that we have no clear nor distinct idea of substance abstracted from properties, the thing is so true, that we can form no idea of substance at all abstracted from properties. But it is also true, that we can form no idea of properties abstracted from substance. The ideas both of substance and of quality are perfectly in the same condition in this respect; which it is surprising philosophers should so little attend to. At the same time, we have clear and distinct ideas of many things as they exist, though perhaps we have not a complete idea of any one thing. We have such ideas of things as serve to all the useful purposes of life. It is true, our senses reach not beyond the external properties of beings. We have no direct perception of the essence and internal properties of any thing. These we discover from the effects produced. But had we senses to perceive directly the essence and internal properties of things, our idea of them would indeed be more full and complete, but not more clear and distinct, than at present. For, even upon that supposition, we could form no notion of substance, but by its properties, internal and external. To form an idea of a thing abstracted from all its properties, is impossible.
The following is the sum of what is above laid down. By sight and touch we have the perceptions of substance and body, as well as of qualities. It is not figure, extension, motion, that we perceive; but a thing figured, extended, and moving. As we cannot form an idea of substance abstracted from qualities, so we cannot form an idea of qualities abstracted from sub-stance. They are relative ideas, and imply each other.
Primary and Secondary Qualities
Philosophers are pretty much agreed about primary qualities, that they are such as inhere in a body or substance, and exist with the body or substance intirely independent of us. According to that definition, primary qualities are objects of the senses of sight and touch, and of these only. Therefore secondary qualities, if these have any meaning, must be objects of the other senses: whether so or not, shall by and by be examined. According to these definitions, figure, size, solidity, and divisibility without end, are primary qualities. All of them belong to a substance or body; and are as much independent of us, as the substance or body itself. Holding gravity to be a tendency in every particle of matter to unite with every other particle, it may justly be considered as a primary quality: a tendency to motion, it is true, is properly a power; but a power to act is a property or quality, and may well be held a capital one. The vis inertiae is a power in matter to resist a change from rest to motion. The vis incita is another power, tending to make a body persevere in that degree of motion which is impressed upon it. These powers also may be added to the list of primary qualities. Colour at first view seems to be a primary quality, as we can as little conceive a body without colour as without figure. And yet, upon search we find nothing on the surface of a body but particles variously figured and combined, which have not the most distant resemblance to colour. These particles indeed, by reflecting rays of light on the eye, may produce a perception of colour in the beholder; but that perception cannot be a quality of the object, primary or secondary. Heat, whether a pleasant or painful feeling, cannot be in the fire, an inanimate body incapable of feeling. A power in fire to raise such a feeling, may indeed be classed among the primary qualities; and so may a power in a body to raise a perception of colour: but a cause ought not to be confounded with its effect.
According to the analysis here given, a sound, a smell, a taste, existing no where but in the mind of a percipient, cannot be qualities of a body, either primary or secondary. Mr. Locke however endeavours to make them secondary qualities by converting them into powers. “Colour, he says, is not a quality as it appears to be, but a power in matter to raise in us the perception of colour.”* In the same manner, sweetness must be a power in sugar to raise a perception of sweetness, and sound must be a power in a drum to raise a perception of sound. But this account of secondary qualities is unsatisfactory, as evidently converting an effect into its cause. A mental perception, as observed above, can in no proper sense be held a quality of the object perceived. And could this perception be converted into a power inherent in the object perceived, it would be a primary quality, not a secondary.
These insuperable objections notwithstanding, all men agree to place the perceptions mentioned, not in the mind where they really exist, but in the bodies that produce them; and for that reason, and for that only, are they held to be secondary qualities. Nothing is more familiar among the learned as well as among the vulgar, than to conceive sweetness to be a quality of sugar, a fragrant smell to be a quality of the rose, and colour to be a quality of all bodies. Now if this illusion be the only foundation of secondary qualities, they must be defined perceptions in the mind of man, which by an illusion of nature are placed upon external objects.
Nature never goes out of the direct road in vain. This illusion must be contrived for some valuable purpose that cannot be obtained in the direct road. Consider what would be the face of nature did we perceive nothing around us but bodies and their primary qualities as they really exist, without any notion of what are termed secondary qualities. It is difficult to conceive a scence with which we are intirely unacquainted; but upon the slightest reflection it will appear cold and insipid. How little attractive would a beautiful woman be, were the pure red and white of her skin and her melodious accents, perceived to be no where but in the mind of her lover! Upon that supposition, how slight would be the influence of an orator or of a general harranguing his army! Conversation would be much less entertaining, were we conscious that the sounds we hear proceed not from the speaker. A rose would be little regarded, were it known that it has no fragrancy of smell. To sum up all in a single view, were this delusive curtain withdrawn, men, finding no pleasure but within, would be intirely occupied with internal objects, without paying any regard to their external causes. Society would be greatly relaxed, and selfish passions would prevail without any antagonist. It is much easier to conceive and to paint objects as they appear to us. We are placed as in a fairy land full of enchantments. Behold that flower-parterre, insipid in itself and void of ornament, yet cloathed apparently with splendid colours, in perfect harmony! It is a wonderful artifice to present objects to the eye in various attires, so as to be distinguished and remembered; and to paint on the fancy gay and lively, grand and striking, sober and melancholy scenes, whence many agreeable and affecting emotions arise. Yet all this beauty of colour is a mere illusion, a sort of enchantment. The illusion of sound has still greater influence. Listen to an orator pouring out instruction in all the harmony of sound, different tones suited to the variety of his subject. Listen to a musician ravishing the heart with his melodious strains. It is this illusion that makes the charm of conversation: thoughts passing from one to another, would have little influence, if the speaker did not command attention by variety of tones high and low. How sweet and how vivifying is the smell of a polished field producing the most fragrant flowers! In a word, this illusion is the cement of society, connecting men and things together in an amiable union.
I had almost forgot to add, that though pain and pleasure can exist no where but in the mind, yet the pain occasioned by any disorder of the body, is by this illusion placed on the part affected; by which we are directed to apply the cure to that part.
The relation that things have to each other, afford an instance of a similar illusion. Equality, uniformity, resemblance, proximity, are relations that depend not on us, but exist whether perceived or not; and upon that account may properly be termed primary relations. Propriety and impropriety, congruity and incongruity, are perceptions of an internal sense, having no existence in the objects perceived. But as these perceptions are, by an illusion of nature, placed in the objects and conceived as belonging to them, they may therefore be termed secondary relations.
Veracity of the External Senses
The external senses serve two very different purposes, one to give information of things that concern us, and one to entertain us. With respect to the latter, handled in the section immediately foregoing, as enjoyment is intended not truth, it derogates not from our nature, that an illusion is happily employed for our good. A painter, who by the art of perspective, gives to a plain surface the appearance of hills and valleys, deserves praise for entertaining us, not blame as a deceiver. With respect to the former purpose, nature determines us to rely on the evidence of our senses; and they never deceive us when in a sound state. The senses chiefly intended to make us acquainted with things external, are sight and touch. These senses afford absolute conviction of the reality of their objects. By both we perceive external things existing independent of us. I see a white horse grazing in a field: I lift a book in the dark lying on my table. I can no more doubt of their existence than of my own. It is not even in my power to conceive that the Almighty can give me more satisfactory evidence. And the veracity of my perceptions is confirmed by constant experience. I see a tree of a certain shape and size. Advancing to it, I find it in its place by the resistance it makes to my body. I see it day after day, year after year; and find the object to be the same, with no variation but what the seasons and time produce. The tree is at last cut down: it is no longer seen nor felt.
The eye is nicely formed for seeing objects distinctly at the most convenient distance. A microscopic eye gives an accurate view of objects at hand, but reaches not distant objects: a telescopic eye enlarges our sphere of vision, but cannot take in minute objects. The eyes of the generality are accurately formed for a medium distance, that which is the most useful. It is true, that we see things differently at different distances and through different media. But that imperfection, if it can be termed so, is so on corrected by experience, and never betrays us into any hurtful error. By a diseased eye, we sometimes see things different from what they are in reality, as in a jaundice, which makes objects appear yellow; but even here the error appears upon the slightest reflection. In a word, there is nothing to which all men are more necessarily determined, than to put confidence in their senses. Their information is relied on; and we trust our lives and fortunes upon it, with perfect assurance. We entertain no doubt of their veracity, being so constituted as not to have it in our power to doubt.
When the veracity of our senses is thus founded on the necessity of our nature and confirmed by constant experience, it cannot but appear strange, that it should come into the thought of any man to call it in question. But the influence of novelty is great; and when a man of a bold genius, in spite of common sense, will strike out new paths to himself, it is not easy to foresee how far his airy metaphysical notions may carry him. A late author, who gives us a treatise concerning the principles of human knowledge, strikes at the root of the veracity of our senses, by denying the reality of external objects; and thereby paves the way to the most inveterate scepticism.2 For what reliance can we have upon our senses, if they deceive us in a point so material? If we can be prevailed upon to doubt of the reality of external objects, the next step will be, to doubt of what passes in our own mind, of the reality of our ideas and perceptions; for we have not a clearer conviction of the one than of the other. And the last step will be, to doubt of our own existence; for it is shown in a former essay, that we have no certainty of this fact, but what depends upon sense and feeling.
It is reported, that Dr. Berkeley, the author of the above-mentioned treatise, was moved to adopt this whimsical opinion, to evade some arguments urged by materialists against the existence of the Deity. If so, he was in bad luck; for this doctrine, if it should not lead to universal scepticism, affords at least a shrewd argument in favour of Atheism. If I can only be conscious of what passes in my own mind, and if I cannot trust my senses when they give me notice of external and independent existences; it follows, that I am the only being in the world; at least, that I can have no evidence from my senses, of any other being, body or spirit. This is certainly an unwary concession; because it deprives us of our chief means for attaining knowledge of the Deity. Laying aside sense and feeling, this learned divine will find it a difficult task, to point out by what other means we discover the foregoing important truth. But of this more afterward.
Were there nothing else in view but to establish the reality of external objects, it would be scarce worth while to bestow much thought in solving metaphysical paradoxes against their existence, which are better confuted by common sense and experience. But as the foregoing doctrine appears to have very extensive consequences, and to strike at the root of the most valuable branches of human knowledge; an attempt to re-establish the veracity of our senses, by detecting the fallacy of the arguments that have been urged against it, may, it is hoped, not be unacceptable to the public. The attempt at any rate is necessary in this work; the main purpose of which is, to show, that our senses, external and internal, are the chief sources from whence the knowledge of the Deity is derived to us.
The author mentioned boldly denies the existence of matter, and the reality of the objects of external sense; contending, that there is nothing really existing without the mind of an intelligent being; in a word, reducing all to be a world of ideas. “It is an opinion strangely prevailing among men,” says he, “that houses, mountains, rivers, and in a word all sensible objects have an existence, natural or real, distinct from their being perceived by the understanding.” He ventures to call this a manifest contradiction; and his argument against the reality of these objects, is in the following words:
The forementioned objects are things perceived by sense. We cannot perceive any thing but our own ideas or perceptions; therefore what we call men, houses, mountains, &c. can be nothing else but ideas or perceptions.3
This argument shall be examined afterward with the respect that is due to its author. It shall only be taken notice of by the way, that, supposing mankind to be under so strange a delusion as to mistake their ideas for men, houses, mountains, it will not follow, that there is in this any manifest contradiction, or any contradiction at all. For deception is a very different thing from contradiction. But he falls from this high pretension in the subsequent part of his work, to argue more consistently, “that, supposing solid, figured, and moveable substances, to exist without the mind, yet we could never come to the knowledge of this.”* Which is true, if our senses bear no testimony of the fact. And he adds,† “that, supposing no bodies to exist without the mind, we might have the very same reasons for supposing the existence of external bodies that we have now.” Which may be true, supposing our senses to be fallacious.
The Doctor’s fundamental proposition is, That we can perceive nothing but our own ideas or perceptions. Of this assertion he hath not even attempted a proof; though, in so bold an undertaking as that of annihilating the whole universe, his own mind excepted, he had no reason to hope, that an assertion so singular and so contradictory to common sense, would be taken upon his word. It may be true, that it is not easy to explain, nor even to comprehend, by what means we perceive external objects. But our ignorance is in most cases a very lame argument against fact. At this rate, he may take upon him equally to deny many operations in the material world, which have not hitherto been explained by him or others. At the same time, it is perhaps as difficult to explain the manner of perceiving our own ideas, or the impressions made upon us, as to explain the manner of perceiving external objects. The Doctor beside ought to have considered, that by this bold doctrine he sets bounds to the power of nature, or of the Author of nature. If it was in the power of the Almighty to bestow upon man a faculty of perceiving external objects, he has done it. We have indeed no conception how external objects could be more clearly manifested to us than in fact they are. Therefore the Doctor was in the right to assert, that a faculty in man to perceive external objects would be a contradiction, and consequently a privilege not in the power of the Deity to bestow upon him. He perceived the necessity of carrying his argument so far: sensible however that this was not to be made out, he never once attempts to point at any thing like a contradiction. And if he cannot prove it to be a contradiction, the question is at an end: for supposing only the fact to be possible, we have the very highest evidence of its reality that our nature is capable of, namely the testimony of our senses.
It hath been urged in support of this doctrine, that nothing is present to the mind but the impressions made upon it; and that it cannot be conscious of any thing but what is present. This difficulty is easily solved. For the proposition, “That we cannot be conscious of any thing but what is present to the mind, or passes within it,” is taken for granted, as if it were self-evident: and yet the direct contrary is an evident fact, that we are conscious of many things which are not present to the mind; that is, which are not, like perceptions and ideas, within the mind. Nor is there any difficulty to conceive, that an impression may be made upon us by an external object, so as to raise a direct perception of the external object itself. When we attend to the operations of the external senses, we discover that external objects make not impressions all of them in the same manner. In some instances we feel the impression, and are conscious of it as an impression. In others, being quite unconscious of the impression, we perceive only the external object. And to give full satisfaction to the reader upon the present subject, it may perhaps not be fruitless, briefly to run over the operations of the several external senses, by which the mind is made conscious of external objects, and of their properties.
And, first, with regard to the sense of smelling, which gives us no notice of external existences. Here the operation is of the simplest kind. It is no more but an impression made at the organ, which makes me perceive a smell. Experience, it is true, and habit, lead me to ascribe it to some external thing as its cause. But that this connection is the child of experience only, will be evident from the following considerations; that when a new smell is perceived, we are utterly at a loss what cause to ascribe it to; and that when a child feels a smell, it is not led to ascribe it to any cause whatever.
In the senses of tasting and touching, we are conscious not only of the impression made at the organ, but also of the body that makes the impression. When I lay my hand upon this table, the impression is of a hard smooth body that resists the motion of my hand. In this impression, there is nothing to create the least suspicion of fallacy. The body acts where it is, and it acts merely by resistance. We have, from that sense, the fullest and clearest perception of external existences that can be conceived, subject to no doubt, ambiguity, nor even cavil. And this perception must at the same time, support the veracity of our other senses, when they give us notice of external existences.
What remains is the sense of seeing, which it is presumed the Doctor had chiefly in view, when he argues against the reality of external existences. Here there occurs a difficulty, which possibly has had weight with our author, tho’ not once mentioned by him. It is, that no being can act but where it is; and that a body at a distance cannot act upon the mind, more than the mind upon it. This appears to evince the necessity of some inter mediate means in the act of vision; and one is suggested by a fact. The image of a visible object is painted upon the retina of the eye; which puts the operation of vision, in one respect, upon the same footing with that of touching, both being performed by means of an impression made at the organ. There is indeed this difference, that the impression of touch is felt, whereas the impression of sight is not felt: we are not conscious of any impression, but singly of the object itself that makes the impression.
And here a curious circumstance presents itself to view. Though an impression probably is made upon the mind by means of the image painted upon the retina, whereby the external object is perceived; yet nature hath concealed this impression from us in order to remove all ambiguity, and to give us a distinct perception of the object itself, and of that only. In touching and tasting, the impression made at the organ creates no confusion nor ambiguity, the body that makes the impression being perceived as operating where it really is. But were the impression of a visible object perceived as made on the retina, which is the organ of sight, all objects must be seen as within the eye. It is doubted among naturalists, whether outness or distance be at all discoverable by sight, and whether that appearance be not the effect of experience. But bodies and their operations are so closely connected in place, that were we conscious of an organic impression at the retina, the mind would have a constant propensity to place the body there also; which would be a circumstance extremely perplexing in the act of vision, as setting feeling and experience in perpetual opposition; enough to poison all the pleasure we enjoy by that noble sense.
In so short-sighted a creature as man, it is the worst reason in the world for denying any well-attested fact, that we cannot account how it is brought about. We cannot explain how the intervention of rays of light, lays open to our view the beings and things around us: but it is great arrogance, to pretend to doubt of the fact upon that account, for it is in effect maintaining, that there is nothing in nature but what we can explain.
The perception of objects at a distance by intervention of rays of light, involves no inconsistency nor impossibility: and unless that could be asserted, we have no reason to call in question the evidence of the perception. And after all, this particular step of the operation of vision, is not more difficult to be conceived or accounted for, than the other steps, of which no man entertains a doubt. It is perhaps not easy to explain how the image of an external body is painted upon the retina tunica; and no person can explain how that image is communicated to the mind. Why then should we hesitate about the last step, to wit, the perception of external objects, more than about the two former, when they are all equally supported by unexceptionable evidence? The whole operation of vision far surpasses human knowledge; but not more than the operation of magnetism, electricity, and a thousand other natural appearances: our ignorance of the cause, ought not to make us suspect deceit in the one, more than in the other.
Whether our perception of external objects correspond to truth, or whether it be a mere illusion, is a question that cannot be ascertained one way or other by reasoning. But it is ascertained by a higher degree of evidence, to wit, intuitive conviction, which admits not the slightest doubt of the veracity of our senses. It is clear, that supposing the reality of external objects, we can form no conception of their being displayed to us in a more lively and convincing manner, than in fact is done. Why then call a thing in doubt, of which we have as good evidence as human nature is capable of receiving? But we cannot call it in doubt, otherways than in speculation, and even then but for a moment. We have a thorough conviction of the reality of external objects: it rises to the highest certainty; and we act in consequence of it with the greatest security of not being deceived. Nor are we in fact deceived. When we put the matter to a trial, every experiment answers to our perceptions, and confirms us more and more in our belief.
I close this Essay with a comparison between the evidence of our senses and that of human testimony. That we ought not to give credit to any man’s testimony because some men fail in veracity, would be a very lame argument. The only effect such instances have, or ought to have, is to correct our propensity to believe, and to bring on a habit of suspending belief till circumstances be examined. The evidence of our senses rises undoubtedly much above that of human testimony: and if we put trust in the latter after many instances of being deceived, we have better reason to put trust in the former, were the instances of being deceived equally numerous; which is plainly not the fact. When people are in sound health of mind and body, they are very seldom misled by their senses.
[1. ]See “Of Our Complex Ideas of Substances,” in Locke, Essay, II. xxiii.
[* ]Book 2. chap. 22. [Locke, Essay, II. xxiii.4, p. 297.]
[* ]Book 2. chap. 8. § 10. [Not verbatim, but Kames’s paraphrase of Locke’s definition of secondary qualities as those which are “nothing in the Objects themselves, but Powers to produce various Sensations in us by their primary Qualities, i.e. by the Bulk, Figure, Texture, and Motion of their insensible parts, as Colours, Sounds, Tasts, etc.”(Essay,II. viii.10, p. 142).]
[2. ]George Berkeley (1685–1753), A Treatise Concerning the Principles of Human Knowledge (1710; reprint, ed. Jonathan Dancy, New York: Oxford University Press, 1998).
[3. ]Berkeley, Principles, sec. 4, p. 104.
[* ]Sect. 18. [Berkeley, Principles, p. 109.]
[† ]Sect. 20. [Ibid.]