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Of Dr. Reid's Speculations on the Subje&t of Perception.
IT was chiefly in consequence of the sceptical conclusions which Bishop Berkeley and Mr. Hume had deduced from the ancient theories of perception, that Dr. Reid was led to call them in question; and he
appears to me to have shewn, in the most satisfactory manner, not only that they are perfectly hypothetical, but that the suppositions they involve, are absurd and impossible. His reasonings, on this part of our constitution, undoubtedly form the most important accession which the philosophy of the hu. man mind has received since the time of Mr. Locke.
But although Dr. Reid has been at niuch pains to overturn the old ideal fyftem, he has not ventured to substitute any hypothesis of his own in its place. And, indeed, he was too well acquainted with the limits prescribed to our philosophical inquiries, to think of indulging his curiosity, in such unprofitable speculations. All, therefore, that he is to be understood as aiming at, in his inquiries concerning our perceptive powers is, to give a precise state of the fact, divested of all theoretical expressions ; in order to prevent philosophers from imposing on themselves any longer, by words without meaning ; and to extort from them an acknowledgment, that, with respect to the process of nature in perception, they are no less ignorant than the vulgar.
According to this view of Dr. Reid's reasonings, on the subject of perception, the purpose to which they are subservient may appear to fome to be of no very considerable importance; but the truth is, th one of the most valuable effects of genuine phi. lofophy, is to remind us of the limited powers of the human understanding; and to revive those natural feelings of wonder and admiration, at the fpectacle of the universe, which are apt to languilh, in consequence of long familiarity. The most profound discoveries which are placed within the reach of our researches lead to a confession of human ignorance ; for, while they flatter the pride of man, and increase his power, by enabling him to trace the simple and beautitul laws by which physical events are regulated, they call his attention, at the same time, to those general and ultimate facts which bound the narrow circle of his knowledge ; and which, by evincing to him the operation of powers, whose nature must
for ever remain unknown, serve to remind him of the insufficiency of his faculties to penetrate the secrets of the univerle. Wherever we direct our in quiries; whether to the anatomy and physiology of animals, to the growth of vegetables, to the chemical attractions and repulsions, or to the motions of the heavenly hodies; we perpetually perceive the effects of powers which cannot belong to matter.
To a certain length we are able to proceed ; but in every research, we meet with a line, which no industry nor ingenuity can pass. It is a line too, which is marked with fufficient diftinctness; and which no man now thinks of pafling, who has just views of the nature and object of philosophy. It forms the separation between that field which falls under the survey of the physical inquirer, and that unknown region, of which, though it was necessary that we should be afsured of the existence, in order to lay a foundation for the doctrines of natural theology, it hath not pleased the Author of the universe to reveal to us the wonders, in this infant state of our being. It was, in fact, chiefly by tracing out this line, that Lord Bacon did so much service to science.
Besides this effect, which is common to all our philofophical pursuits, of impressing the mind with a fense of that mysterious agency, or efficiency, into
which general laws must be resolved ; they have a tendency, in many cases, to counteract the influence of habit, in weakening those emotions of wonder and of curiosity, which the appearances of nature are so admirably fitted to excite. For this purpose, it is necessary, either to lead the attention to facts which are calculated to strike by their novelty, or to present familiar appearances in a new light; and such are the obvious effects of philosophical inquiries; fometimes extending our views to objects which are removed from vulgar observation; and sometimes correcting our first apprehensions with respect to ordinary events. The communication of motion by impulse, (as I already hinted,) is as unaccountable as any phenomenon we know; and yet, moft men are disposed to consider it, as a fact which does not refult from will, but from necessity. To such men, it may be useful to direct their attention to the uni. versal law of gravitation ; which, although not more wonderful in itself, than the common effects of impulse, is more fitted, by its novelty, to awaken their attention, and to excite their curiosity. If the theo. ry
of Boscovich should ever be established on a satisfactory foundation, it would have this tendency in a ftill more remarkable degree, by teaching us that the communication of motion by impulse, (which we are apt to confider as a nécessary truth,) has no existence whatever ; and that every case in which it appears to our senses to take place, is a phenomenon no less inexplicable, than that principle of attraction which binds together the most remote parts of the universe.
If such, however, be the effects of our philofophical pursuits when successfully conducted, it must be confeffed that the tendency of imperfect or erroneous theories is widely different. By a specious folution of insuperable difficulties, they fu dazzle and bewilder the understanding, as, at once, to prevent
us from advancing, with steadiness, towards the limit of human knowledge ; and from perceiving the existence of a region beyond it, into which philofophy is not permitted to enter. In such cases, it is the business of genuine science to unmak the importure, and to point out clearly, both to the learned and to the vulgar, what reason can, and what she cannot, accomplish. This, I apprehend, has been done, with respect to the history of our perceptions, in the most fatisfactory manner, by Dr. Reid. When a person little accustomed to metaphysical fpeculations is told, that, in the case of volition, there are certain invisible fluids, propagated from the mind to the organ which is moved ; and that, in the case of perception, the existence and qualities of the external object are made known to us by means of species, or phantasms, or images, which are present to the mind in the sensorium ; he is apt to conclude, that the intercourse between mind and matter is much less mysterious than he had fupposed; and that, although these expressions may not convey to him any very diftinct meaning, their import is perfectly understood by philosophers. It is now, I think, pretty generally acknowledged by physiologists, that the influence of the will over the body, is a mystery which has never yet been unfolded ; but, fingular as it may appear, Dr. Reid was the first person who had courage to lay completely afide all the common hypothetical language concerning perception, and to exhibit the difficulty in all its magnitude, by a plain statement of the fact. To what then, it may be asked, does this statement amount ?-Merely to this ; that the mind is fó for. med, that certain impressions produced on our organs of sense by external objects, are followed by correspondent sensations; and that these sensations, (which have no more resemblance to the qualities of matter, than the words of a language have to the
things they denote,) are followed by a perception of the existence and qualities of the bodies by which the impressions are made ; that all the steps of this process are equally incomprehensible ; and that, for any thing we can prove to the contrary, the connexion between the sensation and the perception, as well as that belween the impression and the sensation, may be both arbitrary : that it is therefore by no means imposible, that our sensations may be merely the occasions on which the correspondent perceptions are excited; and that at any rate, the confideration of these sensations, which are attributes of mind, can throw no light on the manner in which we acquire our knowledge of the existence and qualities of body. From this view of the subject, it follows, that it' is external objects themselves, and not any species or images of these objects, that the mind perceives ; and that although, by the constitution of our nature, certain sensations are rendered the constant antecedents of our perceptions, it is just as difficult to explain how our perceptions are obtained by their means, as it would be, upon the supposition, that the mind were all at once inspired with them, without any concomitant sensations whatever.
These remarks are general, and apply to all our various perceptions; and they evidently strike at the root of all the common theories upon the sub. ject. The laws, however, which regulate these perceptions, are different in the case of the different senses, and form a very curious object of philofophical inquiry.--Those, in particular, which regulate the acquired perceptions of sight, lead to some very interesting and important speculations; and, I think, have never yet been explained in a manner completely satisfoctory. To treat of them in detail, does not fall under the plan of this work; buI shall have occasion to make a few remarks on them, in the chapter on Conception.