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existence of a material world, which is done by all those of the primary ones.-And we can, accordingly, conceive matter capa. ble of existing without the secondary, but not without the primary qualities. The sensations of all the primary qualities suggest the local situations of their exciting causes. It is not so with the se. condary; for even those of taste, and of heat and cold, do not so originally, or if we abstract them from touch. To the perception of all the primary qualities, actual, or sensible contact is neces. sary; whilst all the secondary are, or may be, perceived through a medium.
I may remark here, although colour seems to be that one of the secondary qualities, without which we find it most difficult to conceive matter capable of existing, that this difficulty (arising, indeed, from early association) will immediately vanish when we consider, that persons born blind do, and must, conceive every sort of body to exist without any colour at all; of which, indeed, they can form no idea, or notion, except, perhaps, some.. thing like that of the blind man who compared a scarlet colour to the sound of a trumpet. With respect to the secondary qualities of heat and cold, we can easily conceive a body without its being hot, and another without its being cold; and we know, if we apply the hand to a body at the same temperature with itself, and of a similar conducting power, that it will produce no sensation of heat or of cold. Indeed the pen with which I write, conveys at present to my fingers no sensation (which I can distinguish) to be that of one, or the other.
In a subsequent part of these inquiries it will be shewn, that our sensations are sometimes agreeable, or disagreeable; whilst, at other times the external quality, or cause, is so, and not the Sensation or Perception. When the Sensation is agreeable or disagreeable, we generally find, that it is one of those that correspond to the secondary qualities, of the secondary senses, smell, taste, or hearing; to which we must add the sensations of the secondary qualities, heat and cold. When, on the contrary, the external qualities, and not the sensations, happen to be agreeable or disagreeable, we find that it is not the qualities suggested by the secondary sensations, but the primary qualities, at least in general, that have this effect. Thus the sensations corresponding to the primary qualities,--hardness, softness, roughness, smoothness, extension, solidity, figure, motion, and weight*, in general attract no attention at all, and are scarcely noticed ; whilst we pass over instantaneously from their sensations to contemplate the qualities themselves; by some of which, particularly by figure, or form, roughness and smoothness, hardness and softness, we are usually affected with agreeable or disagreeable emotions. To these I must add the names of visible beauty and deformity, form, proportion, motion, and, perhaps, colour. If these observations be correct, in the case of the secondary qualities, it is not the qualities but the sensations that are agreeable or disagreeable; whereas, in the case of the primary qualities, this peculiarity be. Jongs always to the qualities themselves, and not to the sensations. It deserves also to be remarked on this subject, that as we attend not to the sensations of the primary qualities, but to themselves, so, also, that we know little or nothing of those sensations, and can scarcely make them distinct and separate objects of attention, whilst the qualities themselves seem to be pretty correctly understood by all mankind*: whereas, on the contrary, with respect to the secondary qualities, the sensations of which of. ten attract our attention as much as their causes t, we know little more, than that they constitute a certain class of unknown powers, or properties, in external objects, which, from experience, we learn to be the causes of some of our sensations. . But I would not have it imagined from these remarks, that I am of opinion, that our comparative ignorance of these unknown causes is owing to this, that our attention is so much more engaged by their sensations than by those of the primary qualities, any more than I would have it thought, that our knowledge of the primary quali. ties is owing to our neglect of their corresponding sensations, and attention to themselves, In both cases the effect and its contrary character are to be ascribed, not to the attention and industry of man, but to the mysterious wisdom of Nature. .
* Since weight is a primary quality of matter, we cannot sufficiently wonder at the systematic prejudices of those chemists, who, in their zeal for phlogiston, could stuinble upon a thing so inconceivable and absurd as 4 principle of absolute levity, which they supposed to be material.
Conformably to some of the preceding remarks, we find, that the primary qualities are generally as well known and understood nearly by the vulgar, as they are by philosophers, and that, too, from their early years; whilst all that is generally known of the secondary qualities is, that they are the external, unknown causes of certain sensations. Nor does this knowledge of the primary qualities seem to be the result of much attention and study, or to be acquired by reflecting on the corresponding sensations and reasoning from them, as some philosophers seem to think,--for it is always acquired at a very early, and, of course, a very ignorant period of life; whereas, on the contrary, all that we know of the secondary qualities, besides their being the unknown
* Reid's Essays on the Intellectual Powers of Man, Ess. II. ch. xvii. + Reid's Inquiry, &c. Cb. II. sect. ix; and his Essays, as above.
causes of some of our sensations (and we have acquired consider. able knowledge of some of them) is the result of much attention, of many experiments, and of long study, observation, and reasoning. It deserves also to be mentioned, that, from the very first, we give to the primary qualities an external and permanent existence, altogether independent of our sensations; and that the notions we form of them, from the sensations by which they are suggested, have not in general any reference to these sensations. It was partly this consideration, I think, which suggested the following remark :-" That we have notions of external qualities perfectly unlike to our sensations, or to any thing of which we are immediately conscious, is a fact; nor ought we to dispute the reality of what we perceive, because we cannot reconcile this fact with received philosophical systems *.” On the contrary, the existence, which we allow to the secondary qualities, is merely relative, since at first we know only that they are the causes of certain sensations; and any thing more than this we can then hardly conceive about them t.
Our different sensations and perceptions not only suggest to us the existence of external objects, as their causes, but also frequently produce in our minds such agreeable or disagreeable feelings, as to make us wish for the repetition and continuation of some of them, as anxiously as we do for the perpetual exclusion and absence of others. When the sensations happen to be agreeable or disagreeable, they will be found to be those, in general, corresponding to the secondary qualities; whilst the sensations excited by the primary qualities have so little of any thing agreeable or disagreeable in them that they scarcely attract any notice at all. This peculiarity, which affords us additional reasons for making a distinction between primary and secondary qualities, deserves to be more fully investigated than it has generally been. A diversity, or contrariety of effect, so manifest in cases appa. rently similar, since it is the work of Nature, has not been estab. lished without an intention of its being subservient to some wise, beneficent purpose. It is now generally allowed, that the primary sensations have generally nothing either agreeable or disa. greeable in them : in other words, that they seldom affect us either with pleasure or pain ; and were this even not generally ad. mitted, we could infer it from the fact of their being almost never attended to. The truth seems to be, that the sensations corTesponding to the primary qualities were intended by Nature to perform merely the office of signs; and this being the case, if she had not left them indifferent, as we find she has done, but
Stewart's Outlines of Moral Philosophy. + Reid's Latellectual Powers of Man, Essay II. ch. xvii.
made them, like the sensations of the secondary qualities, partly agreeable and partly disagreeable, she would, in a great measure, have frustrated her own wise purposes. Agreeably to this view of the subject we find, that we acquire in early life an habitual inattention to these primary sensations, which we cannot by any means altogether get over, in its more advanced stages. (See Reid's Works, Vol. I. Essay II. ch. xvi.] Besides the considera. tion, that this class of sensations were left in themselves indifferent, and are not attended to, whilst the qualities suggested by them are always much attended to, there are others also which contribute to shew, that they were intended to perform the office of signs. Thus we know that they have not in any language a name, whilst their causes have always distinct names, and that too in all languages *. Further, the names of the secondary setsations are all ambiguous, signifying either the sensation or its external unknown cause : which circumstance added to this, that the sensations of the secondary qualities are partly agreeable and partly disagreeable, and thus, of course, require attention, proves that they were not by Nature intended to perform the office of signs, at least not in the same sense with the sensations excited by the primary qualities; otherwise she would have given them a character altogether similar to that of the primary, and instead of making their names ambigious, as is the case in all languages, she would have given distinct and separate names, like those of the primary, to the qualities suggested, or to the unknown external causes of the secondary sensations, whilst she would have left the secondary sensations themselves like the primary, and as they ought to be in order to perform the office of signs, uninviting, unnoticed, and without a name. The following remarks by Dr. Reid will serve to confirm these observations:
6 We may see (says he) why the sensations belonging to the 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 oc. casions 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
* See Reid's Essays, Vol. I. ;His Inquiry, &c.; and Stewart's Quts lines of Moral Philosopby.
is perceived, the sensation immediately leads our thoughts to the quality perceived 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 *".
The primary sensations having no names, whilst those of the corresponding are distinct, and they themselves well kuown and understood +, there cannot be in this case room for any confusion. or ambiguity. But, with respect to the secondary qualities and sensations, the case is far otherwise: as the names of these are in all languages ambiguous, being equally used to designate the sensations and their causes.-It is to this circumstance, accordingly, that we must recur for an explanation of the Cartesian paradoxical opinion, concerning the non-existence of odours, tastes, sounds, and colours, &c.-All our sensations and perceptions perform the office of signs; suggesting either what is going on in the mind, or without us. It is only when our sensations are agreeable or disagreeable, that we are led to attend to themselves.-As they are meant for signs, we in general attend more to what is suggested by them, as we attend more to the meaning, than to the words of a language.-But, since sensation, perception, and the external object succeed one another uniformly, with such inconceivable rapi. dity, it often happens that the sensation and its cause get the same
-Besides this, the sensation, in order to attract attention, must be somewhat agreeable or disagreeable; and where this is the case (as it seems to be with all the secondary sensations, ex. cept that of colour), we sometimes give it the same name as to its external cause, as in the case of the secondary qualities, and sometimes a very different one ; for instance, the feeling excited by the cut of a sword we call pain. But where the sensation is indifferent, it attracts no notice, and we give it no name: thus the sensations of the primary qualities have not a name in any language.--The ambiguity, then, in the case of secondary quali. ties, arises not from any resemblance of the sensations to their causes, but from these circumstances; that, in Perception, they and their causes are constantly conjoined, and because these causes are obscure, and but very little known or understood.
Having said that the sensations corresponding to the primary qualities are not in general either agreeable or disagreeable, but indifferent, as they ought to be, in order to perform the office of
Reid's Works, Vol. I. Essay ii. ch. xvii. ; and Scoli's Elements of Intellectual Philosophy, Chap. II. sect. ii.
+ Reid's Warks, ibid.
# Dr. Reid's Works, passim; and Scott'ş Elements of Intellectual Philosophy,