Des Cartes and Locke, attending more to the operations of their own minds, say, that the sensations by which we have notice of secondary qualities have no resemblance to anything that pertains to body; but they did not see that this might, with equal justice, be applied to the primary qualities. [234] Mr Locke maintains, that the sensations we have from primary qualities are resemblances of those qualities. This shews how grossly the most ingenious men may err with regard to the operations of their minds. It must, indeed, be acknowledged, that it is much easier to have a distinct notion of the sensations that belong to secondary than of those that belong to the primary qualities. The reason of this will appear in the next chapter. But, had Mr Locke attended with suffi. cient accuracy to the sensations+ which he was every day and every hour receiving from primary qualities, he would have seen that they can as little resemble any quality of an inanimated being as pain can resemble a cube or a circle. What had escaped this ingenious philosopher, was clearly discerned by Bishop Berkeley. He had a just notion of sensations, and saw that it was impossible that anything in an insentient being could resemble them; a thing so evident in itself, that it seems wonderful that it should have been so long unknown. But let us attend to the consequence of this discovery. Philosophers, as well as the vulgar, had been accustomed to comprehend both sensation and perception under one name, and to consider them as one uncompounded operation. Philosophers, even more than the vulgar, gave the name of sensation to the whole operation of the senses; and all the notions we have of material things were called ideas of sensation. This led Bishop Berkeley to take one ingredient of a complex operation for the whole; and, having clearly discovered the nature of sensation, taking it for granted that all that the senses present to the mind is sensation, which can have no resemblance to anything material, he concluded that there is no material world. [235] If the senses furnished us with no materials of thought but sensations, his conclusion must be just; for no sensation can give us the conception of material things, far less species impressa and species expressa, the distinction of sensation and perception could be perceived; but, in point of fact, many even of the Aristotelians, who admitted species at all, allowed them only in one or two of the senses. See Notes D ** and M.-H. The reader will observe that Reid says, "dis tinct notion of the sensations that belong to the se. condary qualities," and not distinct notion of the secondary qualities themselves.-H. Here again the reader will observe that the term is sensations, and not notions, of the primary qualities.-H. any argument to prove their existence. But, if it is true that by our senses we have not only a variety of sensations, but likewise a conception and an immediate natural conviction of external objects, he reasons from a false supposition, and his arguments fall to the ground. CHAPTER XVII. OF THE OBJECTS OF PERCEPTION; AND, FIRST, OF PRIMARY AND SECONDARY QUALITIES. The objects of perception are the various qualities of bodies. Intending to treat of these only in general, and chiefly with a view to explain the notions which our senses give us of them, I begin with the distinction between primary and secondary qualities. These were distinguished very early. The Peripatetic system confounded them, and left no difference. The distinction was again revived by Des Cartes and Locke, and a second time abolished by Berkeley and Hume. If the real foundation of this distinction can be pointed out, it will enable us to account for the various revolutions in the sentiments of philosophers concerning it. Every one knows that extension, divisibility, figure, motion, solidity, hardness, softness, and fluidity, were by Mr Locke called primary qualities of body; and that sound, colour, taste, smell, and heat or cold, were called secondary qualities. Is there a just foundation for this distinction? there anything common to the primary which belongs not to the secondary? And what is it? Is I answer, That there appears to me to be a real foundation for the distinction; and it is this-that our senses give us a direct and a distinct notion of the primary qualities, and inform us what they are in themselves.+ But of the secondary qualities, our senses give us only a relative and obscure notion. [236] They inform us only, that they are qualities that affect us in a certain manner —that is, produce in us a certain sensation; but as to what they are in themselves, our senses leave us in the dark.+ *On this whole distinction, see Note D. **.-H. ↑ By the expression," what they are in themselves," In reference to the primary qualities, and of "rela tive notion," in reference to the secondary, Reid cannot mean that the former are known to us absolutely and in themselves—that is, out of relation to our cognitive faculties; for he elsewhere admits that all our knowledge is relative. Farther, if" our senses give us a direct and distinct notion of the primary qualities, and inform us what they are in themselves," these qualities, as known, must resemble, or be iden. tical with, these qualities as existing-H. The distinctions of perception and sensation, and of primary and secondary qualities, may be reduced to one higher price ple. Knowledge is partly objective, partly subjective; both these elements are essen. tial to every cognition, but in every cognition they are always in the inverse ratio of each other. Now Every man capable of reflection may easily satisfy himself that he has a perfectly clear and distinct notion of extension, divisibility, figure, and motion. The solidity of a body means no more but that it excludes other bodies from occupying the same place at the same time. Hardness, softness, and fluidity are different degrees of cohesion in the parts of a body. It is fluid when it has no sensible cohesion; soft, when the cohesion is weak; and hard, when it is strong. Of the cause of this cohesion we are ignorant, but the thing itself we understand perfectly, being immediately informed of it by the sense of touch. It is evident, therefore, that of the primary qualities we have a clear and distinct notion; we know what they are, though we may be ignorant of their causes. I observed, farther, that the notion we have of primary qualities is direct, and not relative only. A relative notion of a thing, is, strictly speaking, no notion of the thing at all, but only of some relation which it bears to something else. sentient. The quality in the rose is something which occasions the sensation in me; but what that something is, I know not. My senses give me no information upon this point. The only notion, therefore, my senses give is this-that smell in the rose is an unknown quality or modification, which is the cause or occasion of a sensation which I know well. The relation which this unknown quality bears to the sensation with which nature hath connected it, is all I learn from the sense of smelling; but this is evidently a relative notion. The same reasoning will apply to every secondary quality. Thus, I think it appears that there is a real foundation for the distinction of primary from secondary qualities; and that they are distinguished by this—that of the primary we have by our senses a direct and distinct notion; but of the secondary only a relative notion, which must, because it is only relative, be obscure; they are conceived only as the unknown causes or occa sions of certain sensations with which we are well acquainted. The account I have given of this distinction is founded upon no hypothesis. [238] Whether our notions of primary qualities are direct and distinct, those of the secondary relative and obscure, is a matter of fact, of which every man may have certain knowledge by attentive reflection upon them. To this reflection I appeal, as the proper test of what has been advanced, and proceed to make some reflections on this subject. Thus, gravity sometimes signifies the tendency of bodies towards the earth; sometimes it signifies the cause of that tendency. When it means the first, I have a direct and distinct notion of gravity; I see it, and feel it, and know perfectly what it is; but this tendency must have a cause. We give the same name to the cause; and that cause has been an object of thought and of speculation. Now, what notion have we of this cause when we think and reason about it? It is evident we think of it as an unknown cause, of a known effect. This is a relative notion; and it must be obscure, because itations. gives us no conception of what the thing is, but of what relation it bears to something else. Every relation which a thing unknown bears to something that is known, may give a relative notion of it; and there are many objects of thought and of discourse of which our faculties can give no better than a relative notion. [237] Having premised these things to explain what is meant by a relative notion, it is evident that our notion of primary qualities is not of this kind; we know what they are, and not barely what relation they bear to something else. It is otherwise with secondary qualities. If you ask me, what is that quality or modification in a rose which I call its smell, I am at a loss to answer directly. Upon reflection, I find, that I have a distinct notion of the sensation which it produces in my mind. But there can be nothing like to this sensation in the rose, because it is in in perception and the primary qualities, the objective ele ent preponderates, whereas the subjective eleent preponderates in sensation and the secondary Lalities. See Notes D and D **.-H. 1. The primary qualities are neither sensations, nor are they resemblances of sens This appears to me self-evident. I have a clear and distinct notion of each of the primary qualities. I have a clear and distinct notion of sensation. I can compare the one with the other; and, when I do so, I am not able to discern a resembling feature. Sensation is the act or the feeling (I dispute not which) of a sentient being. Figure, divisibility, solidity, are neither acts nor feelings. Sensation supposes a sentient being as its subject; for a sensation that is not felt by some sentient being, is an absurdity. Figure and divisibility supposes a subject that is figured and divisible, but not a subject that is sentient. 2. We have no reason to think that any of the secondary qualities resemble any sensation. The absurdity of this notion has been clearly shewn by Des Cartes, Locke, and many modern philosophers. It was a tenet of the ancient philosophy, and is still by many imputed to the vulgar, but only as a vulgar error. It is too evident to need proof, that the vibrations of a sounding body do not resemble the sensation of sound, nor the effluvia of an odorous body the sensation of smell. 3. The distinctness of our notions of primary qualities prevents all questions and disputes about their nature. There are no different opinions about the nature of extension, figure, or motion, or the nature of any primary quality. Their nature is manifest to our senses, and cannot be unknown to any man, or mistaken by him, though their causes may admit of dispute. [239] The primary qualities are the object of the mathematical sciences; and the distinctness of our notions of them enables us to reason demonstratively about them to a great extent. Their various modifications are precisely defined in the imagination, and thereby capable of being compared, and their relations determined with precision and certainty. It is not so with secondary qualities. Their nature not being manifest to the sense, may be a subject of dispute. Our feeling informs us that the fire is hot; but it does not inform us what that heat of the fire is. But does it not appear a contradiction, to say we know that the fire is hot, but we know not what that heat is? I answer, there is the same appearance of contradiction in many things that must be granted. We know that wine has an inebriating quality; but we know not what that quality is. It is true, indeed, that, if we had not some notion of what is meant by the heat of fire, and by an inebriating quality, we could affirm nothing of either with understanding. We have a notion of both; but it-is only a relative notion. We know that they are the causes of certain known effects. 4. The nature of secondary qualities is a proper subject of philosophical disquisition; and in this philosophy has made some progress. It has been discovered, that the sensation of smell is occasioned by the effluvia of bodies; that of sound by their vibration. The disposition of bodies to reflect a particular kind of light, occasions the sensation of colour. Very curious discoveries have been made of the nature of heat, and an ample field of discovery in these subjects remains. 5. We may see why the sensations belonging to secondary qualities are an object of our attention, while those which belong to the primary are not. The first are not only signs of the object perceived, but they bear a capital part in the notion we form of it. [240] We conceive it only as that which occasions such a sensation, and therefore cannot reflect upon it without thinking of the sensation which it occasions: we have no other mark whereby to distinguish it. The thought of a secondary quality, therefore, always carries us back to the sensation which it produces. We give the same name to both, and are apt to confound them together. But, having a clear and distinct conception of primary qualities, we have no need, when we think of them, to recall their sensations. When a primary quality is perceived, the sensation immediately leads our thought to the quality signified by it, and is itself forgot. We have no occasion afterwards to reflect upon it; and so we come to be as little acquainted with it as if we had never felt it. This is the case with the sensations of all primary qualities, when they are not so painful or pleasant as to draw our attention. When a man moves his hand rudely against a pointed hard body, he feels pain, and may easily be persuaded that this pain is a sensation, and that there is nothing resembling it in the hard body; at the same time, he perceives the body to be hard and pointed, and he knows that these qualities belong to the body only. In this case, it is easy to distinguish what he feels from what he perceives. Let him again touch the pointed body gently, so as to give him no pain; and now you can hardly persuade him that he feels anything but the figure and hardness of the body: so difficult it is to attend to the sensations belonging to primary qualities, when they are neither pleasant nor painful. They carry the thought to the external object, and immediately disappear and are forgot. Nature intended them only as signs; and when they have served that purpose they vanish. We are now to consider the opinions both of the vulgar and of philosophers upon this subject. [241] As to the former, it is not to be expected that they should make distinctions which have no connection with the common affairs of life; they do not, therefore, distinguish the primary from the secondary qualities, but speak of both as being equally qualities of the external object. Of the primary qualities they have a distinct notion, as they are immediately and distinctly, perceived by the senses; of the secondary, their notions, as I apprehend, are confused and indistinct, rather than erroneous. A secondary quality is the unknown cause or occasion of a well-known effect; and the same name is common to the cause and the effect. Now, to distinguish clearly the different ingredients of a complex notion, and, at the same time, the different meanings of an ambiguous word, is the work of a philosopher; and is not to be expected of he vulgar, when their occasions do not require it. I grant, therefore, that the notion which the vulgar have of secondary qualities, is indistinct and inaccurate. But there seems to be a contradiction between the vulgar and the philosopher upon this subject, and each charges the other with a gross ab surdity. The vulgar say, that fire is hot, and snow cold, and sugar sweet; and that to deny this is a gross absurdity, and contradicts the testimony of our senses. The philosopher says, that heat, and cold, and sweetness, are nothing but sensations in our minds; and it is absurd to conceive that these sensations are in the fire, or in the snow, or in the sugar. I believe this contradiction, between the vulgar and the philosopher, is more apparent than real; and that it is owing to an abuse of language on the part of the philosopher, and to indistinct notions on the part of the vulgar. The philosopher says, there is no heat in the fire, meaning that the fire has not the sensation of heat. His meaning is just; and the vulgar will agree with him, as soon as they understand his meaning: But his language is improper; for there is really a quality in the fire, of which the proper name is heat; and the name of heat is given to this quality, both by philosophers and by the vulgar, much more frequently than to the sensation of heat. [242] This speech of the philosopher, therefore, is meant by him in one sense; it is taken by the vulgar in another sense. In the sense in which they take it, it is indeed absurd, and so they hold it to be. In the sense in which he means it, it is true; and the vulgar, as soon as they are made to understand that sense, will acknowledge it to be true. They know, as well as the philosopher, that the fire does not feel heat: and this is all that he means by saying there is no heat in the fire. In the opinions of philosophers about primary and secondary qualities, there have been, as was before observed, several revolutions. They were distinguished, long before the days of Aristotle, by the sect called Atomists: among whom Democritus made a capital figure. In those times, the name of quality was applied only to those we call secondary qualities; the primary, being considered as essential to matter, were not called qualities. That the atoms, which they held to be the first principles of things, were extended, solid, figured, and movable, there was no doubt; but the question was, whether they had smell, taste, and colour? or, as it was commonly expressed, whether they had qualities? The Atomists maintained, that they had not; that the qualities were not in bodies, but were something resulting from the operation of bodies upon our senses.§ All this ambiguity was understood and articu. ately explained by former philos phers. See above, notes at pp 205 and 310, and No è D.-H. +See Note D.-H. The Atomists derived the qualitative attributes of things from the quantitative -H. Still Democritus suppose! certain real or ob. Jective causes for the subjective differences of our It would seem that, when men began to speculate upon this subject, the primary qualities appeared so clear and manifest that they could entertain no doubt of their existence wherever matter existed; but the secondary so obscure that they were at a loss where to place them. They used this comparison: as fire, which is neither in the flint nor in the steel, is produced by their collision, so those qualities, though not in bodies, are produced by their impulse upon our senses. [243] This doctrine was opposed by Aristotle." He believed taste and colour to be substantial forms of bodies, and that their species, as well as those of figure and motion, are received by the senses.† In believing that what we commonly call taste and colour, is something really inherent in body, and does not depend upon its being tasted and seen, he followed nature. But, in believing that our sensations of taste and colour are the forms or species of those qualities received by the senses, he followed his own theory, which was an absurd fiction.+ Des Cartes not only shewed the absurdity of sensible species received by the senses, but gave a more just and more intelligible account of secondary qualities than had been given before. Mr Locke followed him, and bestowed much pains upon this subject. He was the first, I think, that gave them the name of secondary qualities, which has been very generally adopted. He distinguished the sensation from the quality in the body, which is the cause or occasion of that sensation, and shewed that there neither is nor can be any similitude between them.§ By this account, the senses are acquitted of putting any fallacy upon us; the sensation is real, and no fallacy; the quality in the body, which is the cause or occasion of this sensation, is likewise real, though the nature of it is not manifest to our senses. If we impose upon ourselves, by confounding the sensation with the quality that occasions it, this is owing to rash judgment or weak understanding, but not to any false testimony of our senses. This account of secondary qualities I take sensations Thus, in the different forms, positions, and relations of atoms, he sought the ground of difference of tastes, colours, heat and cold, &c. See Theophrastus De Sensu, 65-Aristotle De Anima, 2.-Galen De Elementis-Simplicius in Phys. i Auscult. libros, f. 119, b.-H. * Aristotle admitted that the doctrine in question was true, of colour, taste, &c., as nar' ivigyuay, but not true of them as κατὰ δύναμιν. See De Anima ii. 2.-H. This is not really Aristotle's doctrine.-H. Locke only gave a new meaning to old terms. The first and second or the primary and secondary qualities of Aristotle, denoted a distinction similar to, but not identical with, that in question-H. He distinguished nothing which had not been more precisely discriminated by Aristotle and the Cartesians.-H. to be very just; and if Mr Locke had stopped here, he would have left the matter very clear. But he thought it necessary to introduce the theory of ideas, to explain the distinction between primary and secondary qualities, and by that means, as I think, perplexed and darkened it. When philosophers speak about ideas, we are often at a loss to know what they mean by them, and may be apt to suspect that they are mere fictions, that have no existence. [244] They have told us, that, by the ideas which we have immediately from our senses, they mean our sensations. These, indeed, are real things, and not fictions. We may, by accurate attention to them, know perfectly their nature; and, if philosophers would keep by this meaning of the word idea, when applied to the objects of sense, they would at least be more intelligible. Let us hear how Mr Locke explains the nature of those ideas, when applied to primary and secondary qualities, Book 2, chap 8, § 7, tenth edition. "To discover the nature of our ideas the better, and to discourse of them intelligibly, it will be convenient to distinguish them, as they are ideas, or perceptions in our minds, and as they are modifications of matter in the bodies that cause such perceptions in us, that so we may not think (as perhaps usually is done) that they are exactly the images and resemblances of something inherent in the subject; most of those of sensation being, in the mind, no more the likeness of something existing without us, than the names that stand for them are the likeness of our ideas, which yet, upon hearing, they are apt to excite in us.' This way of distinguishing a thing, first, as what it is; and, secondly, as what it is not, is, I apprehend, a very extraordinary way of discovering its nature. And if ideas are ideas or perceptions in our minds, and, at the same time, the modifications of matter in the bodies that cause such perceptions in us, it will be no easy matter to discourse of them intelligibly. The discovery of the nature of ideas is carried on in the next section, in a manner no less extraordinary. "Whatsoever the mind perceives in itself, or is the immediate object of perception, thought, or understanding, that I call idea; and the power to produce any idea in our mind, I call quality of the subject wherein that power is. Thus, a snowball having the power to produce in us the ideas of white, cold, and round the powers to produce those ideas The Cartesians, particularly Malebranche, dis. tinguished the Idea and the Feeling (sentiment, sensatio.) Of the primary qualities in their doctrine we have Ideas; of the secondary, only Feelings.-H. This and some of the following strictures on Locke are rather hypercritical.-H. in us, as they are in the snowball, I call qualities; and, as they are sensations, or perceptions in our understandings, I call them ideas; which ideas, if I speak of them sometimes as in the things themselves, I would be understood to mean those qualities in the objects which produce them in us." [245] These are the distinctions which Mr Locke thought convenient, in order to discover the nature of our ideas of the qualities of matter the better, and to discourse of them intelligibly. I believe it will be difficult to find two other paragraphs in the essay so unintelligible. Whether this is to be imputed to the intractable nature of ideas, or to an oscitancy of the author, with which he is very rarely chargeable, I leave the reader to judge. There are, indeed, several other passages in the same chapter, in which a like obscurity appears; but I do not chuse to dwell upon them. The conclusion drawn by him from the whole is, that primary and secondary qualities are distinguished by this, that the ideas of the former are resemblances or copies of them, but the ideas of the other are not resemblances of them. Upon this doctrine, I beg leave to make two observations. First, Taking it for granted that, by the ideas of primary and secondary qualities, he means the sensations they excite in us, I observe that it appears strange, that a sensation should be the idea of a quality in body, to which it is acknowledged to bear no resemblance. If the sensation of sound be the idea of that vibration of the sounding body which occasions it, a surfeit may, for the same reason, be the idea of a feast. A second observation is, that, when Mr Locke affirms, that the ideas of primary qualities—that is, the sensations they raise in us-are resemblances of those qualities, he seems neither to have given due attention to those sensations, nor to the nature of sensation in general. [246] Let a man press his hand against a hard body, and let him attend to the sensation he feels, excluding from his thought every thing external, even the body that is the cause of his feeling. This abstraction, indeed, is difficult, and seems to have been little, if at all practised. But it is not impossible, and it is evidently the only way to understand the nature of the sensation. due attention to this sensation will satisfy A |