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case of apparent contact, are the most general facts we observe among the terrestrial phenomena ; and they are, of all physical events, those which are the most familiar to us from our earliest infancy. It was therefore not only natural, but proper, that philosophers should begin their physical inquiries with attempting to refer to these, (which are the most general laws of nature, exposed to the examination of our senses,) the particular appearances they wished to explain. And if ever the theory of Boscovich should be completely established, it will have no other effect than to resolve these laws into some principle still more general, without affecting the solidity of the common doctrine so far as it goes.



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 human mind has received since the time of Mr. Locke.

But although Dr. Reid has been at much pains to overturn the old ideal system, 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 some to be of no very considerable importance ; but the truth is, that one of the most valuable effects of genuine philosophy, is to remind us of the limited powers of the human understanding; and to revive those natural feelings of wonder and admiration at the spectacle of the universe, which are apt to languish 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 beautiful 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 universe. Wherever we direct our inquiries,—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 bodies,—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 sufficient distinctness, and which no man now thinks of passing 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 assured 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.

Beside this effect, which is common to all our philosophical pursuits, of impressing the mind with a sense 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, sometimes 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 most men are disposed to consider it as a fact which does not result from will but from necessity. To such men it may be useful to direct their attention to the universal 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 theory of Boscovich should ever be established on a satisfactory foundation, it would have this tendency in a still more remarkable degree, by teaching us that the communication of motion by impulse (which we are apt to consider as a necessary 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 philosophical pursuits when successfully conducted, it must be confessed that the tendency of imperfect or erroneous theories is widely different. By a specious solution of insuperable difficulties, they so 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 philosophy is not permitted to enter. In such cases, it is the business of genuine science to unmask the imposture, 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 satisfactory manner, by Dr. Reid. When a person little accustomed to metaphysical speculations 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 supposed ; and that, although these expressions may not convey to him any very distinct 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, singular as it may appear, Dr. Reid was the first person who had courage to lay completely aside 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 so formed 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 anything we can prove to the contrary, the connexion between the sensation and the perception, as well as that between the impression and the sensation, may be both arbitrary; that it is therefore by no means impossible that our sensations may be merely the occasions on which the correspondent perceptions are excited; and that, at

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any rate, the consideration 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 the 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, yet 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.1

These remarks are general, and apply to all our various perceptions, and they evidently strike at the root of all the commmon theories upon the subject. The laws, however, which regulate these perceptions are different in the case of the different senses, and form a very curious object of philosophical 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 satisfactory. To treat of them in detail, does not fall under the plan of this work; but I shall have occasion to make a few remarks on them in the chapter on Conception.

In opposition to what I have here observed on the importance


[This language has been objected to, as bordering on mysticism, whereas, in truth, it is merely a statement of a fact, accompanied with an acknowledgment of our total ignorance of the manner in which it is to be explained. Is it any thing more than an extension to the phenomena of perception, of what Mr. Hume has so justly and so profoundly remarked concerning the phenonena of voluntary motion? “Is THERE PRINCIPLE IN ALL NATURE MORE MYSTERIOUS THAN THE UNION OF SOUL AND BODY, BY WHICH A SUPPOSED SPIRITUAL

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