Front Page Titles (by Subject) III.—: KNOWLEDGE AND REALITY - Selections from the Scottish Philosophy of Common Sense
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III.—: KNOWLEDGE AND REALITY - Thomas Reid, Selections from the Scottish Philosophy of Common Sense 
Selections from the Scottish Philosophy of Common Sense, edited, with an introduction by G.A. Johnston (Chicago: Open Court, 1915).
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KNOWLEDGE AND REALITY
Hardness of bodies is a thing that we conceive as distinctly, and believe as firmly, as anything in nature. We have no way of coming at this conception and belief, but by means of a certain sensation of touch, to which hardness hath not the least similitude; nor can we, by any rules of reasoning, infer the one from the other. The question is, How we come by this conception and belief?
First, as to the conception: Shall we call it an idea of sensation, or of reflection? The last will not be affirmed; and as little can the first, unless we will call that an idea of sensation which hath no resemblance to any sensation. So that the origin of this idea of hardness, one of the most common and most distinct we have, is not to be found in all our systems of the mind: not even in those which have so copiously endeavoured to deduce all our notions from sensation and reflection.
But, secondly, supposing we have got the conception of hardness, how came we by the belief of it? Is it self-evident, from comparing the ideas, that such a sensation could not be felt, unless such a quality of bodies existed? No. Can it be proved by probable or certain arguments? No; it cannot. Have we got this belief, then, by tradition, by education, or by experience? No; it is not got in any of these ways. Shall we then throw off this belief as having no foundation in reason? Alas! it is not in our power; it triumphs over reason, and laughs at all the arguments of a philosopher. Even the author of the Treatise of Human Nature, though he saw no reason for this belief, but many against it, could hardly conquer it in his speculative and solitary moments; at other times, he fairly yielded to it, and confesses that he found himself under a necessity to do so.
What shall we say, then, of this conception, and this belief, which are so unaccountable and untractable? I see nothing left, but to conclude, that, by an original principle of our constitution, a certain sensation of touch both suggests to the mind the conception of hardness, and creates the belief of it: or, in other words, that this sensation is a natural sign of hardness. And this I shall endeavour more fully to explain.
Of Natural Signs
As in artificial signs there is often neither similitude between the sign and thing signified, nor any connection that arises necessarily from the nature of the things, so it is also in natural signs. The word gold has no similitude to the substance signified by it; nor is it in its own nature more fit to signify this than any other substance; yet, by habit and custom, it suggests this and no other. In like manner, a sensation of touch suggests hardness, although it hath neither similitude to hardness, nor, as far as we can perceive, any necessary connection with it. The difference betwixt these two signs lies only in this—that, in the first, the suggestion is the effect of habit and custom; in the second, it is not the effect of habit, but of the original constitution of our minds.
It appears evident from what hath been said on the subject of language, that there are natural signs as well as artificial; and particularly, that the thoughts, purposes, and dispositions of the mind, have their natural signs in the features of the face, the modulation of the voice, and the motion and attitude of the body: that, without a natural knowledge of the connection between these signs and the things signified by them, language could never have been invented and established among men: and, that the fine arts are all founded upon this connection, which we may call the natural language of mankind. It is now proper to observe, that there are different orders of natural signs, and to point out the different classes into which they may be distinguished, that we may more distinctly conceive the relation between our sensations and the things they suggest, and what we mean by calling sensations signs of external things.
The first class of natural signs comprehends those whose connection with the thing signified is established by nature, but discovered only by experience. The whole of genuine philosophy consists in discovering such connections, and reducing them to general rules. The great Lord Verulam had a perfect comprehension of this, when he called it an interpretation of nature. No man ever more distinctly understood or happily expressed the nature and foundation of the philosophical art. What is all we know of mechanics, astronomy, and optics, but connections established by nature, and discovered by experience or observation, and consequences deduced from them? All the knowledge we have in agriculture, gardening, chemistry, and medicine, is built upon the same foundation. And if ever our philosophy concerning the human mind is carried so far as to deserve the name of science, which ought never to be despaired of, it must be by observing facts, reducing them to general rules, and drawing just conclusions from them. What we commonly call natural causes might, with more propriety, be called natural signs, and what we call effects, the things signified. The causes have no proper efficiency or causality, as far as we know; and all we can certainly affirm is, that nature hath established a constant conjunction between them and the things called their effects; and hath given to mankind a disposition to observe those connections, to confide in their continuance, and to make use of them for the improvement of our knowledge, and increase of our power.
A second class is that wherein the connection between the sign and thing signified, is not only established by nature, but discovered to us by a natural principle, without reasoning or experience. Of this kind are the natural signs of human thoughts, purposes, and desires, which have been already mentioned as the natural language of mankind. An infant may be put into a fright by an angry countenance, and soothed again by smiles and blandishments. A child that has a good musical ear, may be put to sleep or to dance, may be made merry or sorrowful, by the modulation of musical sounds. The principles of all the fine arts, and of what we call a fine taste, may be resolved into connections of this kind. A fine taste may be improved by reasoning and experience; but if the first principles of it were not planted in our minds by nature, it could never be acquired. Nay, we have already made it appear, that a great part of this knowledge which we have by nature, is lost by the disuse of natural signs, and the substitution of artificial in their place.
A third class of natural signs comprehends those which, though we never before had any notion or conception of the thing signified, do suggest it, or conjure it up, as it were, by a natural kind of magic, and at once give us a conception and create a belief of it. I shewed formerly, that our sensations suggest to us a sentient being or mind to which they belong—a being which hath a permanent existence, although the sensations are transient and of short duration—a being which is still the same, while its sensations and other operations are varied ten thousand ways—a being which hath the same relation to all that infinite variety of thoughts, purposes, actions, affections, enjoyments, and sufferings, which we are conscious of, or can remember. The conception of a mind is neither an idea of sensation nor of reflection; for it is neither like any of our sensations, nor like anything we are conscious of. The first conception of it, as well as the belief of it, and of the common relation it bears to all that we are conscious of, or remember, is suggested to every thinking being, we do not know how.
The notion of hardness in bodies, as well as the belief of it, are got in a similar manner; being, by an original principle of our nature, annexed to that sensation which we have when we feel a hard body. And so naturally and necessarily does the sensation convey the notion and belief of hardness, that hitherto they have been confounded by the most acute inquirers into the principles of human nature, although they appear, upon accurate reflection, not only to be different things, but as unlike as pain is to the point of a sword.
It may be observed, that, as the first class of natural signs I have mentioned is the foundation of true philosophy, and the second the foundation of the fine arts, or of taste—so the last is the foundation of common sense—a part of human nature which hath never been explained.
I take it for granted, that the notion of hardness, and the belief of it, is first got by means of that particular sensation which, as far back as we can remember, does invariably suggest it; and that, if we had never had such a feeling, we should never have had any notion of hardness. I think it is evident, that we cannot, by reasoning from our sensations, collect the existence of bodies at all, far less any of their qualities. This hath been proved by unanswerable arguments by the Bishop of Cloyne, and by the author of the Treatise of Human Nature. It appears as evident that this connection between our sensations and the conception and belief of external existences cannot be produced by habit, experience, education, or any principle of human nature that hath been admitted by philosophers. At the same time, it is a fact that such sensations are invariably connected with the conception and belief of external existences. Hence, by all rules of just reasoning, we must conclude, that this connection is the effect of our constitution, and ought to be considered as an original principle of human nature, till we find some more general principle into which it may be resolved.1
It is further to be observed, that hardness and softness, roughness and smoothness, figure and motion, do all suppose extension, and cannot be conceived without it; yet, I think it must, on the other hand, be allowed that, if we had never felt any thing hard or soft, rough or smooth, figured or moved, we should never have had a conception of extension; so that, as there is good ground to believe that the notion of extension could not be prior to that of other primary qualities, so it is certain that it could not be posterior to the notion of any of them, being necessarily implied in them all.
Extension, therefore, seems to be a quality suggested to us, by the very same sensations which suggest the other qualities above mentioned. When I grasp a ball in my hand, I perceive it at once hard, figured, and extended. The feeling is very simple, and hath not the least resemblance to any quality of body. Yet it suggests to us three primary qualities perfectly distinct from one another, as well as from the sensation which indicates them. When I move my hand along the table, the feeling is so simple that I find it difficult to distinguish it into things of different natures; yet, it immediately suggests hardness, smoothness, extension, and motion—things of very different natures, and all of them as distinctly understood as the feeling which suggests them.
We are commonly told by philosophers, that we get the idea of extension by feeling along the extremities of a body, as if there was no manner of difficulty in the matter. I have sought, with great pains, I confess, to find out how this idea can be got by feeling; but I have sought in vain. Yet it is one of the clearest and most distinct notions we have; nor is there anything whatsoever about which the human understanding can carry on so many long and demonstrative trains of reasoning.
The notion of extension is so familiar to us from infancy, and so constantly obtruded by everything we see and feel, that we are apt to think it obvious how it comes into the mind; but upon a narrower examination we shall find it utterly inexplicable. It is true we have feelings of touch, which every moment present extension to the mind; but how they come to do so, is the question; for those feelings do no more resemble extension than they resemble justice or courage—nor can the existence of extended things be inferred from those feelings by any rules of reasoning; so that the feelings we have by touch, can neither explain how we get the notion, nor how we come by the belief of extended things.
What hath imposed upon philosophers in this matter is, that the feelings of touch, which suggest primary qualities, have no names, nor are they ever reflected upon. They pass through the mind instantaneously, and serve only to introduce the notion and belief of external things, which, by our constitution, are connected with them. They are natural signs, and the mind immediately passes to the thing signified, without making the least reflection upon the sign, or observing that there was any such thing. Hence it hath always been taken for granted, that the ideas of extension, figure, and motion, are ideas of sensation, which enter into the mind by the sense of touch, in the same manner as the sensation of sound and smell do by the ear and nose. The sensations of touch are so connected, by our constitution, with the notions of extension, figure, and motion, that philosophers have mistaken the one for the other, and never have been able to discern that they were not only distinct things, but altogether unlike. However, if we will reason distinctly upon this subject, we ought to give names to those feelings of touch; we must accustom ourselves to attend to them, and to reflect upon them, that we may be able to disjoin them from, and to compare them with, the qualities signified or suggested by them.
The habit of doing this is not to be attained without pains and practice; and till a man hath acquired this habit, it will be impossible for him to think distinctly, or to judge right, upon this subject.
Let a man press his hand against the table—he feels it hard. But what is the meaning of this?—The meaning undoubtedly is, that he hath a certain feeling of touch, from which he concludes, without any reasoning, or comparing ideas, that there is something external really existing, whose parts stick so firmly together, that they cannot be displaced without considerable force.
There is here a feeling, and a conclusion drawn from it, or some way suggested by it. In order to compare these, we must view them separately, and then consider by what tie they are connected, and wherein they resemble one another. The hardness of the table is the conclusion, the feeling is the medium by which we are led to that conclusion. Let a man attend distinctly to this medium, and to the conclusion, and he will perceive them to be as unlike as any two things in nature. The one is a sensation of the mind, which can have no existence but in a sentient being; nor can it exist one moment longer than it is felt; the other is in the table, and we conclude, without any difficulty, that it was in the table before it was felt, and continues after the feeling is over. The one implies no kind of extension, nor parts, nor cohesion; the other implies all these. Both, indeed, admit of degrees, and the feeling, beyond a certain degree, is a species of pain; but adamantine hardness does not imply the least pain.
And as the feeling hath no similitude to hardness, so neither can our reason perceive the least tie or connection between them; nor will the logician ever be able to shew a reason why we should conclude hardness from this feeling, rather than softness, or any other quality whatsoever. But, in reality, all mankind are led by their constitution to conclude hardness from this feeling.
The sensation of heat, and the sensation we have by pressing a hard body, are equally feelings; nor can we, by reasoning, draw any conclusion from the one but what may be drawn from the other: but, by our constitution, we conclude from the first an obscure or occult quality, of which we have only this relative conception, that it is something adapted to raise in us the sensation of heat; from the second, we conclude a quality of which we have a clear and distinct conception—to wit, the hardness of the body.1
Of the Visible Appearances of Objects
In this section we must speak of things which are never made the object of reflection, though almost every moment presented to the mind. Nature intended them only for signs; and in the whole course of life they are put to no other use. The mind has acquired a confirmed and inveterate habit of inattention to them; for they no sooner appear, than quick as lightning the thing signified succeeds, and engrosses all our regard. They have no name in language; and, although we are conscious of them when they pass through the mind, yet their passage is so quick and so familiar, that it is absolutely unheeded; nor do they leave any footsteps of themselves, either in the memory or imagination. That this is the case with regard to the sensations of touch, hath been shewn in the last chapter; and it holds no less with regard to the visible appearances of objects.1
By colour, all men, who have not been tutored by modern philosophy, understand, not a sensation of the mind, which can have no existence when it is not perceived, but a quality or modification of bodies, which continues to be the same whether it is seen or not. The scarlet-rose which is before me, is still a scarlet-rose when I shut my eyes, and was so at midnight when no eye saw it. The colour remains when the appearance ceases; it remains the same when the appearance changes. For when I view this scarlet-rose through a pair of green spectacles, the appearance is changed; but I do not conceive the colour of the rose changed. To a person in the jaundice, it has still another appearance; but he is easily convinced that the change is in his eye, and not in the colour of the object. Every different degree of light makes it have a different appearance, and total darkness takes away all appearance, but makes not the least change in the colour of the body. We may, by a variety of optical experiments, change the appearance of figure and magnitude in a body, as well as that of colour; we may make one body appear to be ten. But all men believe, that, as a multiplying glass does not really produce ten guineas out of one, nor a microscope turn a guinea into a ten-pound piece, so neither does a coloured glass change the real colour of the object seen through it, when it changes the appearance of that colour.
The common language of mankind shews evidently, that we ought to distinguish between the colour of a body, which is conceived to be a fixed and permanent quality in the body, and the appearance of that colour to the eye, which may be varied a thousand ways, by a variation of the light, of the medium, or of the eye itself. The permanent colour of the body is the cause which, by the mediation of various kinds or degrees of light, and of various transparent bodies interposed, produces all this variety of appearances. When a coloured body is presented, there is a certain apparition to the eye, or to the mind, which we have called the appearance of colour. Mr Locke calls it an idea; and, indeed, it may be called so with the greatest propriety. This idea can have no existence but when it is perceived. It is a kind of thought, and can only be the act of a percipient or thinking being. By the constitution of our nature, we were led to conceive this idea as a sign of something external, and are impatient till we learn its meaning. A thousand experiments for this purpose are made every day by children, even before they come to the use of reason. They look at things, they handle them, they put them in various positions, at different distances, and in different lights. The ideas of sight, by these means, come to be associated with, and readily to suggest, things external, and altogether unlike them. In particular, that idea which we have called the appearance of colour, suggests the conception and belief of some unknown quality in the body which occasions the idea; and it is to this quality, and not to the idea, that we give the name of colour.1
Although there is no resemblance, nor, as far as we know, any necessary connection between that quality in a body which we call its colour, and the appearance which that colour makes to the eye, it is quite otherwise with regard to its figure and magnitude. There is certainly a resemblance, and a necessary connection, between the visible figure and magnitude of a body, and its real figure and magnitude; no man can give a reason why a scarlet colour affects the eye in the manner it does; no man can be sure that it affects his eye in the same manner as it affects the eye of another, and that it has the same appearance to him as it has to another man;—but we can assign a reason why a circle placed obliquely to the eye, should appear in the form of an ellipse. The visible figure, magnitude, and position may, by mathematical reasoning, be deduced from the real; and it may be demonstrated, that every eye that sees distinctly and perfectly, must, in the same situation, see it under this form, and no other. Nay, we may venture to affirm, that a man born blind, if he were instructed in mathematics, would be able to determine the visible figure of a body, when its real figure, distance, and position, are given.1
Since the visible figure of bodies is a real and external object to the eye, as their tangible figure is to the touch, it may be asked, Whence arises the difficulty of attending to the first, and the facility of attending to the last? It is certain that the first is more frequently presented to the eye, than the last is to the touch; the first is as distinct and determinate an object as the last, and seems in its own nature as proper for speculation. Yet so little hath it been attended to, that it never had a name in any language, until Bishop Berkeley gave it that which we have used after his example, to distinguish it from the figure which is the object of touch.
The difficulty of attending to the visible figure of bodies, and making it an object of thought, appears so similar to that which we find in attending to our sensations, that both have probably like causes. Nature intended the visible figure as a sign of the tangible figure and situation of bodies, and hath taught us, by a kind of instinct, to put it always to this use. Hence it happens, that the mind passes over it with a rapid motion, to attend to the things signified by it. It is as unnatural to the mind to stop at the visible figure, and attend to it, as it is to a spherical body to stop upon an inclined plane. There is an inward principle, which constantly carries it forward, and which cannot be overcome but by a contrary force.1
Of Perception in General
Sensation, and the perception of external objects by the senses, though very different in their nature, have commonly been considered as one and the same thing. The purposes of common life do not make it necessary to distinguish them, and the received opinions of philosophers tend rather to confound them; but, without attending carefully to this distinction, it is impossible to have any just conception of the operations of our senses. The most simple operations of the mind, admit not of a logical definition: all we can do is to describe them, so as to lead those who are conscious of them in themselves, to attend to them, and reflect upon them; and it is often very difficult to describe them so as to answer this intention.
The same mode of expression is used to denote sensation and perception; and, therefore, we are apt to look upon them as things of the same nature. Thus, I feel a pain; I see a tree: the first denoteth a sensation, the last a perception. The grammatical analysis of both expressions is the same: for both consist of an active verb and an object. But, if we attend to the things signified by these expressions, we shall find that, in the first, the distinction between the act and the object is not real but grammatical; in the second, the distinction is not only grammatical but real.
The form of the expression, I feel pain, might seem to imply that the feeling is something distinct from the pain felt; yet, in reality, there is no distinction. As thinking a thought is an expression which could signify no more than thinking, so feeling a pain signifies no more than being pained. What we have said of pain is applicable to every other mere sensation. It is difficult to give instances, very few of our sensations having names; and, where they have, the name being common to the sensation, and to something else which is associated with it. But, when we attend to the sensation by itself, and separate it from other things which are conjoined with it in the imagination, it appears to be something which can have no existence but in a sentient mind, no distinction from the act of the mind by which it is felt.
Perception, as we here understand it, hath always an object distinct from the act by which it is perceived; an object which may exist whether it be perceived or not. I perceive a tree that grows before my window; there is here an object which is perceived, and an act of the mind by which it is perceived; and these two are not only distinguishable, but they are extremely unlike in their natures. The object is made up of a trunk, branches, and leaves; but the act of the mind by which it is perceived hath neither trunk, branches, nor leaves. I am conscious of this act of my mind, and I can reflect upon it; but it is too simple to admit of an analysis, and I cannot find proper words to describe it. I find nothing that resembles it so much as the remembrance of the tree, or the imagination of it. Yet both these differ essentially from perception; they differ likewise one from another. It is in vain that a philosopher assures me, that the imagination of the tree, the remembrance of it, and the perception of it, are all one, and differ only in degree of vivacity. I know the contrary; for I am as well acquainted with all the three as I am with the apartments of my own house. I know this also, that the perception of an object implies both a conception of its form, and a belief of its present existence. I know, moreover, that this belief is not the effect of argumentation and reasoning; it is the immediate effect of my constitution.
I am aware that this belief which I have in perception stands exposed to the strongest batteries of scepticism. But they make no great impression upon it. The sceptic asks me, Why do you believe the existence of the external object which you perceive? This belief, sir, is none of my manufacture; it came from the mint of Nature; it bears her image and superscription; and, if it is not right, the fault is not mine: I even took it upon trust, and without suspicion. Reason, says the sceptic, is the only judge of truth, and you ought to throw off every opinion and every belief that is not grounded on reason. Why, sir, should I believe the faculty of reason more than that of perception?—they came both out of the same shop, and were made by the same artist; and if he puts one piece of false ware into my hands, what should hinder him from putting another?1
Our perceptions are of two kinds: some are natural and original; others acquired, and the fruit of experience. When I perceive that this is the taste of cyder, that of brandy; that this is the smell of an apple, that of an orange; that this is the noise of thunder, that the ringing of bells; this the sound of a coach passing, that the voice of such a friend: these perceptions, and others of the same kind, are not original—they are acquired. But the perception which I have, by touch, of the hardness and softness of bodies, of their extension, figure, and motion, is not acquired—it is original.
In all our senses, the acquired perceptions are many more than the original, especially in sight. By this sense we perceive originally the visible figure and colour of bodies only, and their visible place: but we learn to perceive by the eye almost everything which we can perceive by touch. The original perceptions of this sense serve only as signs to introduce the acquired.
The signs by which objects are presented to us in perception, are the language of Nature to man; and as, in many respects, it hath great affinity with the language of man to man, so particularly in this, that both are partly natural and original, partly acquired by custom. Our original or natural perceptions are analogous to the natural language of man to man, of which we took notice in the fourth chapter; and our acquired perceptions are analogous to artificial language, which, in our mother-tongue, is got very much in the same manner with our acquired perceptions—as we shall afterwards more fully explain.
Not only men, but children, idiots, and brutes, acquire by habit many perceptions which they had not originally. Almost every employment in life hath perceptions of this kind that are peculiar to it. The shepherd knows every sheep of his flock, as we do our acquaintance, and can pick them out of another flock one by one. The butcher knows by sight the weight and quality of his beeves and sheep before they are killed. The farmer perceives by his eye, very nearly, the quantity of hay in a rick, or of corn in a heap. The sailor sees the burthen, the build, and the distance of a ship at sea, while she is a great way off. Every man accustomed to writing, distinguishes his acquaintance by their handwriting, as he does by their faces. And the painter distinguishes, in the works of his art, the style of all the great masters. In a word, acquired perception is very different in different persons, according to the diversity of objects about which they are employed, and the application they bestow in observing them.
Perception ought not only to be distinguished from sensation, but likewise from that knowledge of the objects of sense which is got by reasoning. There is no reasoning in perception, as hath been observed. The belief which is implied in it, is the effect of instinct. But there are many things, with regard to sensible objects, which we can infer from what we perceive; and such conclusions of reason ought to be distinguished from what is merely perceived. When I look at the moon, I perceive her to be sometimes circular, sometimes horned, and sometimes gibbous. This is simple perception, and is the same in the philosopher and in the clown: but from these various appearances of her enlightened part, I infer that she is really of a spherical figure. This conclusion is not obtained by simple perception, but by reasoning. Simple perception has the same relation to the conclusions of reason drawn from our perceptions, as the axioms in mathematics have to the propositions. I cannot demonstrate that two quantities which are equal to the same quantity, are equal to each other; neither can I demonstrate that the tree which I perceive, exists. But, by the constitution of my nature, my belief is irresistibly carried along by my apprehension of the axiom; and, by the constitution of my nature, my belief is no less irresistibly carried along by my perception of the tree. All reasoning is from principles. The first principles of mathematical reasoning are mathematical axioms and definitions; and the first principles of all our reasoning about existences, are our perceptions. The first principles of every kind of reasoning are given us by Nature, and are of equal authority with the faculty of reason itself, which is also the gift of Nature. The conclusions of reason are all built upon first principles, and can have no other foundation. Most justly, therefore, do such principles disdain to be tried by reason, and laugh at all the artillery of the logician, when it is directed against them.
When a long train of reasoning is necessary in demonstrating a mathematical proposition, it is easily distinguished from an axiom; and they seem to be things of a very different nature. But there are some propositions which lie so near to axioms that it is difficult to say whether they ought to be held as axioms, or demonstrated as propositions. The same thing holds with regard to perception, and the conclusions drawn from it. Some of these conclusions follow our perceptions so easily, and are so immediately connected with them, that it is difficult to fix the limit which divides the one from the other.
Perception, whether original or acquired, implies no exercise of reason; and is common to men, children, idiots, and brutes. The more obvious conclusions drawn from our perceptions, by reason, make what we call common understanding; by which men conduct themselves in the common affairs of life, and by which they are distinguished from idiots. The more remote conclusions which are drawn from our perceptions, by reason, make what we commonly call science in the various parts of nature, whether in agriculture, medicine, mechanics, or in any part of natural philosophy. When I see a garden in good order, containing a great variety of things of the best kinds, and in the most flourishing condition, I immediately conclude from these signs the skill and industry of the gardener. A farmer, when he rises in the morning, and perceives that the neighbouring brook overflows his field, concludes that a great deal of rain hath fallen in the night. Perceiving his fence broken, and his corn trodden down, he concludes that some of his own or his neighbours’ cattle have broke loose. Perceiving that his stable door is broke open, and some of his horses gone, he concludes that a thief has carried them off. He traces the prints of his horses’ feet in the soft ground, and by them discovers which road the thief hath taken. These are instances of common understanding, which dwells so near to perception that it is difficult to trace the line which divides the one from the other. In like manner, the science of nature dwells so near to common understanding that we cannot discern where the latter ends and the former begins. I perceive that bodies lighter than water swim in water, and that those which are heavier sink. Hence I conclude, that, if a body remains wherever it is put under water, whether at the top or bottom, it is precisely of the same weight with water. If it will rest only when part of it is above water, it is lighter than water. And the greater the part above water is, compared with the whole, the lighter is the body. If it had no gravity at all, it would make no impression upon the water, but stand wholly above it. Thus, every man, by common understanding, has a rule by which he judges of the specific gravity of bodies which swim in water: and a step or two more leads him into the science of hydrostatics.
All that we know of nature, or of existences, may be compared to a tree, which hath its root, trunk, and branches. In this tree of knowledge, perception is the root, common understanding is the trunk, and the sciences are the branches.
Of the Process of Nature in Perception
Although there is no reasoning in perception, yet there are certain means and instruments, which, by the appointment of nature, must intervene between the object and our perception of it; and, by these, our perceptions are limited and regulated. First, If the object is not in contact with the organ of sense, there must be some medium which passes between them. Thus, in vision, the rays of light; in hearing, the vibrations of elastic air; in smelling, the effluvia of the body smelled—must pass from the object to the organ; otherwise we have no perception. Secondly, There must be some action or impression upon the organ of sense, either by the immediate application of the object, or by the medium that goes between them. Thirdly, The nerves which go from the brain to the organ must receive some impression by means of that which was made upon the organ; and, probably, by means of the nerves, some impression must be made upon the brain. Fourthly, The impression made upon the organ, nerves, and brain, is followed by a sensation. And, last of all, This sensation is followed by the perception of the object.
Thus, our perception of objects is the result of a train of operations; some of which affect the body only, others affect the mind. We know very little of the nature of some of these operations; we know not at all how they are connected together, or in what way they contribute to that perception which is the result of the whole; but, by the laws of our constitution, we perceive objects in this, and in no other way.1
Experience teaches us, that certain impressions upon the body are constantly followed by certain sensations of the mind; and that, on the other hand, certain determinations of the mind are constantly followed by certain motions of the body; but we see not the chain that ties these things together. Who knows but their connection may be arbitrary, and owing to the will of our Maker? Perhaps the same sensations might have been connected with other impressions, or other bodily organs. Perhaps we might have been so made as to taste with our fingers, to smell with our ears, and to hear by the nose. Perhaps we might have been so made as to have all the sensations and perceptions which we have, without any impression made upon our bodily organs at all.
However these things may be, if Nature had given us nothing more than impressions made upon the body, and sensations in our minds corresponding to them, we should, in that case, have been merely sentient, but not percipient beings. We should never have been able to form a conception of any external object, far less a belief of its existence. Our sensations have no resemblance to external objects; nor can we discover, by our reason, any necessary connection between the existence of the former, and that of the latter.1
Appendix: Of Cause and Power
It is proper here to explain what is meant by the cause of a phenomenon, when that word is used in natural philosophy. The word cause is so ambiguous, that I fear many mistake its meaning, and take it to mean the efficient cause, which I think it never does in this science.
By the cause of a phenomenon, nothing is meant but the law of nature, of which that phenomenon is an instance, or a necessary consequence. The cause of a body’s falling to the ground is its gravity. But gravity is not an efficient cause, but a general law, that obtains in nature, of which law the fall of this body is a particular instance. The cause why a body projected moves in a parabola, is, that this motion is the necessary consequence of the projectile force and gravity united. But these are not efficient causes; they are only laws of nature. In natural philosophy, therefore, we seek only the general laws, according to which nature works, and these we call the causes of what is done according to them. But such laws cannot be the efficient cause of anything. They are only the rule according to which the efficient cause operates.
A natural philosopher may search after the cause of a law of nature; but this means no more than searching for a more general law, which includes that particular law, and perhaps many others under it. This was all that Newton aimed at by his ether. He thought it possible, that, if there was such an ether, the gravitation of bodies, the reflection and refraction of the rays of light, and many other laws of nature, might be the necessary consequences of the elasticity and repelling force of the ether. But, supposing this ether to exist, its elasticity and repelling force must be considered as a law of nature; and the efficient cause of this elasticity would still have been latent.
Efficient causes, properly so called, are not within the sphere of natural philosophy. Its business is, from particular facts in the material world, to collect, by just induction, the laws that are general, and from these the more general, as far as we can go. And when this is done, natural philosophy has no more to do. It exhibits to our view the grand machine of the material world, analysed, as it were, and taken to pieces, with the connections and dependencies of its several parts, and the laws of its several movements. It belongs to another branch of philosophy to consider whether this machine is the work of chance or of design, and whether of good or of bad design; whether there is not an intelligent first Mover who contrived the whole, and gives motion to the whole, according to the laws which the natural philosopher has discovered, or, perhaps, according to laws still more general, of which we can only discover some branches; and whether he does these things by his own hand, so to speak, or employs subordinate efficient causes to execute his purposes. These are very noble and important inquiries, but they do not belong to natural philosophy; nor can we proceed in them in the way of experiment and induction, the only instruments the natural philosopher uses in his researches.
Whether you call this branch of philosophy Natural Theology or Metaphysics, I care not; but I think it ought not to be confounded with Natural Philosophy; and neither of them with Mathematics. Let the mathematician demonstrate the relation of abstract quantity; the natural philosopher investigate the laws of the material system by induction; and the metaphysician, the final causes, and the efficient causes of what we see and what natural philosophy discovers in the world we live in.
As to final causes, they stare us in the face wherever we cast our eyes. I can no more doubt whether the eye was made for the purpose of seeing, and the ear of hearing, than I can doubt of a mathematical axiom; yet the evidence is neither mathematical demonstration, nor is it induction. In a word, final causes, good final causes, are seen plainly everywhere: in the heavens and in the earth; in the constitution of every animal, and in our own constitution of body and of mind; and they are most worthy of observation, and have a charm in them that delights the soul.
As to efficient causes, I am afraid our faculties carry us but a very little way, and almost only to general conclusions. I hold it to be self-evident, that every production, and every change in nature, must have an efficient cause that has power to produce the effect; and that an effect which has the most manifest marks of intelligence, wisdom, and goodness, must have an intelligent, wise, and good efficient cause. From these, and some such self-evident truths, we may discover the principles of natural theology, and that the Deity is the first efficient cause of all nature. But how far he operates in nature immediately, or how far by the ministry of subordinate efficient causes, to which he has given power adequate to the task committed to them, I am afraid our reason is not able to discover, and we can do little else than conjecture. We are led by nature to believe ourselves to be the efficient causes of our own voluntary actions; and, from analogy, we judge the same of other intelligent beings. But with regard to the works of nature, I cannot recollect a single instance wherein I can say, with any degree of assurance, that such a thing is the efficient cause of such a phenomenon of nature.
I never could see good reason to believe that matter has any active power at all. And, indeed, if it were evident that it has one, I think there could be no good reason assigned for not allowing it others. Your Lordship speaks of the power of resisting motion, and some others, as acknowledged active powers inherent in matter. As to the resistance to motion, and the continuance in motion, I never could satisfy myself whether these are not the necessary consequences of matter being inactive. If they imply activity, they may lie in some other cause.
I am not able to form any distinct conception of active power but such as I find in myself. I can only exert my active power by will, which supposes thought. It seems to me, that, if I was not conscious of activity in myself, I could never, from things I see about me, have had the conception or idea of active power. I see a succession of changes, but I see not the power, that is, the efficient cause of them; but, having got the notion of active power, from the consciousness of my own activity, and finding it a first principle, that every production requires active power, I can reason about an active power of that kind I am acquainted with—that is, such as supposes thought and choice, and is exerted by will. But, if there is anything in an unthinking inanimate being that can be called active power, I know not what it is, and cannot reason about it.
If you conceive that the activity of matter is directed by thought and will in matter, every particle of matter must know the situation and distance of every other particle within the planetary system; but this, I am apt to think, is not your Lordship’s opinion.
I must therefore conclude, that this active power is guided in all its operations by some intelligent Being, who knows both the law of gravitation, and the distance and situation of every particle of matter with regard to every other particle, in all the changes that happen in the material world. I can only conceive two ways in which this particle of matter can be guided, in all the exertions of its active power, by an intelligent Being. Either it was formed, in its creation, upon a foreknowledge of all the situations it shall ever be in with respect to other particles, and had such an internal structure given it, as necessarily produces, in succession, all the motions, and tendencies to motion, it shall ever exert. This would make every particle of matter a machine or automaton, and every particle of a different structure from every other particle in the universe. This is indeed the opinion of Leibnitz; but I am not prejudiced against it upon that account; I only wished to know whether your Lordship adopted it or not. Another way, and the only other way, in which I can conceive the active power of a particle of matter, guided by an intelligent Being, is by a continual influence exerted according to its situation and the situation of other particles. In this case, the particle would be guided as a horse is by his rider; and I think it would be improper to ascribe to it the power of gravitation. It has only the power of obeying its guide. Whether your Lordship chooses the first or the last in this alternative, I should be glad to know; or whether you can think of a third way better than either.1
The ambiguity of the words power, cause, agent, and of all the words related to these, tends to perplex this question. The weakness of human understanding, which gives us only an indirect and relative conception of power, contributes to darken our reasoning, and should make us cautious and modest in our determinations.
We can derive little light in this matter from the events which we observe in the course of nature. We perceive changes innumerable in things without us. We know that those changes must be produced by the active power of some agent; but we neither perceive the agent nor the power, but the change only. Whether the things be active, or merely passive, is not easily discovered. And though it may be an object of curiosity to the speculative few, it does not greatly concern the many.
From the course of events in the natural world, we have sufficient reason to conclude the existence of an eternal intelligent First Cause. But whether He acts immediately in the production of those events, or by subordinate intelligent agents, or by instruments that are unintelligent, and what the number, the nature, and the different offices, of those agents or instruments may be—these I apprehend to be mysteries placed beyond the limits of human knowledge. We see an established order in the succession of natural events, but we see not the bond that connects them together.
Since we derive so little light, with regard to efficient causes and their active power, from attention to the natural world, let us next attend to the moral, I mean to human actions and conduct.
When I observe a plant growing from its seed to maturity, I know that there must be a cause that has power to produce this effect. But I see neither the cause nor the manner of its operation.
But, in certain motions of my body and directions of my thought, I know not only that there must be a cause that has power to produce these effects, but that I am that cause; and I am conscious of what I do in order to the production of them.
From the consciousness of our own activity, seems to be derived not only the clearest, but the only conception we can form of activity, or the exertion of active power.
As I am unable to form a notion of any intellectual power different in kind from those I possess, the same holds with respect to active power. If all men had been blind, we should have had no conception of the power of seeing, nor any name for it in language. If man had not the powers of abstraction and reasoning, we could not have had any conception of these operations. In like manner, if he had not some degree of active power, and if he were not conscious of the exertion of it in his voluntary actions, it is probable he could have no conception of activity, or of active power.
A train of events following one another ever so regularly, could never lead us to the notion of a cause, if we had not, from our constitution, a conviction of the necessity of a cause to every event.
And of the manner in which a cause may exert its active power, we can have no conception, but from consciousness of the manner in which our active power is exerted.
Every man is led by nature to attribute to himself the free determinations of his own will, and to believe those events to be in his power which depend upon his will. On the other hand, it is self-evident, that nothing is in our power that is not subject to our will.
We grow from childhood to manhood, we digest our food, our blood circulates, our heart and arteries beat, we are sometimes sick and sometimes in health; all these things must be done by the power of some agent; but they are not done by our power. How do we know this? Because they are not subject to our will. This is the infallible criterion by which we distinguish what is our doing from what is not; what is in our power from what is not.
Human power, therefore, can only be exerted by will, and we are unable to conceive any active power to be exerted without will. Every man knows infallibly that what is done by his conscious will and intention, is to be imputed to him, as the agent or cause; and that whatever is done without his will and intention, cannot be imputed to him with truth.
We judge of the actions and conduct of other men by the same rule as we judge of our own. In morals, it is self-evident that no man can be the object either of approbation or of blame for what he did not. But how shall we know whether it is his doing or not? If the action depended upon his will, and if he intended and willed it, it is his action in the judgment of all mankind. But if it was done without his knowledge, or without his will and intention, it is as certain that he did it not, and that it ought not to be imputed to him as the agent.
Now it is evident that, to constitute the relation between me and my action, my conception of the action, and will to do it, are essential. For what I never conceived nor willed, I never did.
If any man, therefore, affirms, that a being may be the efficient cause of an action, and have power to produce it, which that being can neither conceive nor will, he speaks a language which I do not understand. If he has a meaning, his notion of power and efficiency must be essentially different from mine; and, until he conveys his notion of efficiency to my understanding, I can no more assent to his opinion than if he should affirm that a being without life may feel pain.
It seems, therefore, to me most probable, that such beings only as have some degree of understanding and will, can possess active power; and that inanimate beings must be merely passive, and have no real activity. Nothing we perceive without us affords any good ground for ascribing active power to any inanimate being; and everything we can discover in our own constitution, leads us to think that active power cannot be exerted without will and intelligence.1
[1 ]Ibid., pp. 121-122.
[1 ]Ibid., pp. 123-125.
[1 ]Ibid., p. 135.
[1 ]Ibid., pp. 137-138.
[1 ]Ibid., pp. 142-143.
[1 ]Ibid., p. 146.
[1 ]Ibid., pp. 182-183.
[1 ]Ibid., pp. 184-186.
[1 ]Ibid., p. 187.
[1 ]“Letter to Lord Kames,” 16th Dec. 1780 (Works, vol. i. pp. 56-59).
[1 ]“Essays on the Active Powers of Man” (Works, vol. ii. pp. 522-525).