Imatges de pàgina
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sure, is that of doing well, and acting the part that becomes us; and the most bitter and painful sentiment, the anguish and remorse of a guilty conscience. These observations, with regard to the economy of nature in the distribution of our painful and agreeable sensations and feelings, are illustrated by the author last mentioned, so elegantly and judiciously, that I shall not attempt to say any thing upon them after him.

I shall conclude this chapter by observing, that as the confounding our sensations with that perception of external objects, which is constantly conjoined with them, has been the occasion of most of the errors and false theories of philosophers with regard to the senses; so the distinguishing these operations seems to me to be the key that leads to a right understanding of both.

Sensation, taken by itself, implies neither the conception nor belief of any external object. It supposes a sentient being, and a certain manner in which that being is affected, but it supposes no more. Perception implies an immediate conviction and belief of something external; something different both from the mind that perceives, and from the act of perception. Things so different in their nature ought to be distinguished; but by our constitution they are always united. Every different perception is conjoined with a sensation that is proper to it. The one is the sign, the other the thing signified. They coalesce in our imagination. They are signified by one name, and are considered as one simple operation. The purposes of life do not require them to be distinguished.

It is the philosopher alone who has occasion to distinguish them, when he would analyse the operation compounded of them. But he has no suspicion that there is any composition in it; and to discover this requires a degree of reflection which has been too little practised even by philosophers.

In the old philosophy, sensation and perception were perfectly confounded. The sensible species coming from the object, and impressed upon the mind, was the whole; and you might call it sensation or perception, as you pleased.

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. Mr. Locke maintains, that the sensations we have from primary qualities are resemblances of those qualities. This shows 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 sufficient 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 any thing 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 any thing material, he concluded that there is no material world.

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 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? Is there any thing common to the primary which belongs not to the secondary? And what is it?

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. 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.

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 observe further, 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.

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 it 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.

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 insentient. 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 occasions of certain sensations with which we are well acquainted.

The account I have given of this distinction is founded upon no hypothesis. 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.

1. The primary qualities are neither sensations, nor are they resemblances of sensations. 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 suppose a subject that is figured and divisible, but not a subject that is sentient.

2. We have no reason to think, that the sensations by which we have notice of secondary qualities resemble any quality of body. The absurdity of this notion has been clearly shown 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.

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. 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 any thing 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. As to the former, it is not to be expected that they should make distinctions which have no connexion 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 the 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 absurdity. 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 lauguage 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. 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

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