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 faculty 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 effect 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 speculation 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 organ 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 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 sen

sations whatever.*

These remarks are general, and apply to all our various percep tions; and they evidently strike at the root of all the common 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 of Dr. Reid's speculations concerning our perceptive powers, I am sensible it may be urged, that they amount merely to a negative discovery; and it is possible, that some may even be forward to remark, that it was unnecessary to employ so much labor and ingenuity as he has done, to overthrow an hypothesis of which a plain account would have been a sufficient refutation. To such

*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 phenomena of voluntary motion? "IS THERE ANY PRINCIPLE IN ALL NATURE MORE MYSTERIOUS THAN THE UNION OF SOUL AND BODY, BY WHICH A SUPPOSED SPIRITUAL SUBSTANCE ACQUIRES SUCH AN INFLUENCE OVER A MATERIAL ONE, THAT THE MOST REFINED THOUGHT IS ABLE TO ACTUATE THE GROSSEST MATTER? WERE WE EMPOWERED, BY A SECRET

WISH, TO REMOVE MOUNTAINS, OR CONTROL THE PLANETS IN THEIR ORBITS, THIS EXTENSIVE AUTHORITY WOULD NOT BE MORE EXTRAORDINARY NOR MORE BEYOND

OUR COMPREHENSION." I do not know that Mr. Hume was ever charged with any tendency to mysticism; and yet the two cases seem to me to be perfectly analogous.

persons, I would beg leave to suggest, that, although, in consequence of the juster views in pneumatology, which now begin to prevail, (chiefly, I believe, in consequence of Dr. Reid's writings,) the ideal system may appear to many readers unphilosophical and puerile; yet the case was very different when this author entered upon his inquiries and I may even venture to add, that few positive discoveries, in the whole history of science, can be mentioned, which found a juster claim to literary reputation, than to have detected, so clearly and unanswerably, the fallacy of an hypothesis, which has descended to us from the earliest ages of philosophy; and which in modern times, has not only served to Berkeley and Hume as the basis of their skeptical systems, but was adopted as an indisputable truth by Locke, by Clarke, and by Newton.

SECTION IV.

Of the Origin of our Knowledge.

THE philosophers who endeavored to explain the operations of the human mind by the theory of ideas, and who took for granted, that in every exertion of thought there exists in the mind some object distinct from the thinking substance, were naturally led to inquire whence these ideas derive their origin; in particular, whether they are conveyed to the mind from without by means of the senses, or form part of its original furniture?

With respect to this question, the opinions of the ancients were various; but as the influence of these opinions on the prevailing systems of the present age is not very considerable, it is not necessary, for any of the purposes I have in view in this work, to consider them particularly. The moderns, too, have been much divided on the subject; some holding with Des Cartes, that the mind is furnished with certain innate ideas; others, with Mr. Locke, that all our ideas may be traced from sensation and reflection; and many, (especially among the later metaphysicians in France,) that they may be all traced from sensation alone.

Of these theories, that of Mr. Locke deserves more particularly our attention; as it has served as a basis of most of the metaphysical systems which have appeared since his time; and as the difference between it and the theory which derives all our ideas from sensation alone, is rather apparent than real.

In order to convey a just notion of Mr. Locke's doctrine concerning the origin of our ideas, it is necessary to remark, that he refers to sensation, all the ideas which we are supposed to receive by the external senses; our ideas, for example, of colors, of sounds, of hardness, of extension, of motion; and, in short, of all the qualities and modes of matter; to reflection, the ideas of our own

mental operations which we derive from consciousness; our ideas, for example, of memory, of imagination, of volition, of pleasure, and of pain. These two sources, according to him, furnish us with all our simple ideas, and the only power which the mind possesses over them, is to preform certain operations, in the way of compo sition, abstraction, generalization, &c., on the materials which it thus collects in the course of its experience. The laudable desire of Mr. Locke, to introduce precision and perspicuity into metaphysical speculations, and his anxiety to guard the mind against error in general, naturally prepossessed him in favor of a doctrine, which, when compared with those of his predecessors, was intelligible and simple; and which by suggesting a method, apparently easy and palpable, of analyzing our knowledge into its elementary principles, seemed to furnish an antidote against those prejudices which had been favored by the hypothesis of innate ideas. It is now a considerable time since this fundamental principle of Mr. Locke's system began to lose its authority in England: and the skeptical conclusions, which it had been employed to support by some later writers, furnished its opponents with very plausible arguments against it. The late learned Mr. Harris, in particular, frequently mentions this doctrine of Mr. Locke, and always in terms of high indignation. "Mark," (says he, in one passage,) "the order of things, according to the account of our later metaphysicians. First comes that huge body, the sensible world. Then this, and its attributes beget sensible ideas. Then, out of sensible ideas, by a kind of lopping and pruning, are made ideas intelligible, whether specific or general. Thus should they admit that mind was coeval with body; yet, till the body gave it ideas, and awakened its dormant powers, it could at best have been nothing more than a sort of dead capacity; for innate ideas it could not possibly have any." And in another passage; "For my own part, when I read the detail about sensation and reflection, and am taught the process at large how my ideas are all generated, I seem to view the human soul, in the light of a crucible, where truths are produced by a kind of logical chemistry."

If Dr. Reid's reasonings on the subject of ideas be admitted, all these speculations with respect to their origin fall to the ground; and the question to which they relate is reduced merely to a question of fact; concerning the occasions on which the mind is first led to form those simple notions into which our thoughts may be analyzed, and which may be considered as the principles or elements of human knowledge. With respect to many of these notions, this inquiry involves no difficulty. No one, for example, can be at a loss to ascertain the occasions on which the notions of colors and sounds are first formed by the mind: for these notions are confined to individuals who are possessed of particular senses, and cannot by any combination of words, be conveyed to those who never enjoyed the use of them. The history of our notions of extension and