dered, by reflection, sufficiently precise and satisfactory to show them the absurdity of attempting to explain the mode of their communication; had yet such a degree of influence on their speculations, as to induce them to exhibit their supposed medium under as mysterious and ambiguous a form as possible, in order that it might remain doubtful to which of the two predicaments, of body or mind, they meant that it should be referred. By refining away the grosser qualities of matter, and by allusions. to some of the most aerial and magical appearances it assumes, they endeavored, as it were, to spiritualize the nature of their medium; while at the same time, all their language concerning it implied such a reference to matter, as was necessary for furnishing a plausible foundation for applying to it the received maxims of natural philosophy. Another observation, too, which was formerly hinted at, is confirmed by the same historical review; that, in the order of inquiry, the phenomena of vision had first engaged the attention of philosophers, and had suggested to them the greater part of their language with respect to perception in general; and that, in consequence of this circumstance, the common modes of expression on the subject, unphilosophical and fanciful at best, even when applied to the sense of seeing, are, in the case of all the other senses, obviously unintelligible and self-contradictory. As to objects of sight, says Dr. Reid, I understand what is meant by an image of their figure in the brain; but how shall we conceive an image of their color, where there is absolute darkness? And, as to all other objects of sense, except figure and color, I am unable to conceive what is meant by an image of them. Let any man say, what he means by an image of heat and cold, an image of hardness or softness, an image of sound, or smell, or taste. The word image, when applied to these objects of sense, has absolutely no meaning. This palpable imperfection in the ideal theory has plainly taken rise from the natural order in which the phenomena of perception present themselves to the curiosity. That in the case of the perception of distant objects, we are naturally inclined to suspect, either something to be emitted from the object to the organ of sense, or some medium to intervene between the object and organ, by means of which the former may communicate an impulse to the latter, appears from the common modes of expression on the subject, which are to be found in all languages. In our own, for example, we frequently hear the vulgar speak of light striking the eye; not in consequence of any philosophical theory they have been taught, but of their own crude and undirected speculations. Perhaps there are few men among those who have attended at all to the history of their own thoughts, who will not recollect the influence of these ideas, at a period of life long prior to the date of their philosophical studies. Nothing, indeed, can be conceived more simple and natural than their origin. When an object is placed in a certain situation with respect to a particular organ of the body, a perception arises in the mind; when the object is removed, the perception ceases. Hence we are led to apprehend some connection between the object and the perception; and as we are accustomed to believe, that matter produces its effects by impulse, we conclude that there must be some material medium intervening between the object and organ, by means of which the impulse is communicated from the one to the other. That this is really the case, I do not mean to dispute. - I think, however, it is evident, that the existence of such a medium does not in any case appear à priori: and yet the natural prejudices of men have given rise to an universal belief of it, long before they were able to produce any good arguments in support of their opinion. Nor is it only to account for the connection between the object and the organ of sense, that philosophers have had recourse to the theory of impulse. They have imagined that the impression on the organ of sense is communicated to the mind, in a similar manner. As one body produces a change in the state of another by impulse, so it has been supposed, that the external object produces perception, (which is a change in the state of the mind,) first, by some material impression made on the organ of sense; and, secondly, by some material impression communicated from the organ to the mind along the nerves and brain. These suppositions, indeed, as I had occasion already to hint, were, in the ancient theories of perception, rather implied than expressed; but by modern philosophers, they have been stated in the form of explicit propositions. "As to the manner," says Mr. Locke, "in which bodies produce ideas in us, it is manifestly by impulse, the only way which we can conceive bodies operate in." Dr. Clark has expressed the same idea still more confidently, in the following passage of one of his letters to Leibnitz. "Without being present to the images of the things perceived, the soul could not possibly perceive them. A living substance can only there perceive, where it is present. Nothing can any more act, or be acted upon, where it is not present, than it can when it is not." "How body acts upon mind, or mind upon body," (says Dr. Porterfield) "I know not; but this I am very certain of, that nothing can act, or be acted upon, where it is not; and therefore our mind can never perceive any thing but its own proper modifications, and the various states of the sensorium, to which it is present: so that it is not the external sun and moon, which are in the heavens, which our mind perceives, but only their image or representation, impressed upon the sensorium. How the soul of a seeing man sees these images, or how it receives those ideas, from such agitations in the sensorium, I know not; but I am sure it can never perceive the external bodies themselves, to which it is not present." -- Theories of perception by Monboddo and Malebranche. The same train of thinking, which had led these philosophers to suppose that external objects are perceived by means of species proceeding from the object to the mind, or by means of some material impression made on the mind by the brain, has suggested to a late writer a very different theory; that the mind, when it perceives an external object, quits the body, and is present to the object of perception. "The mind," (says the learned author of Ancient Metaphysics,) "is not where the body is, when it perceives what is distant from the body, either in time or place, because nothing can act, but when, and where, it is. Now, the mind acts when it perceives. The mind, therefore, of every animal who has memory or imagination, acts, and by consequence exists, when and where the body is not; for it perceives objects distant from the body both in time and place." Indeed, if we take for granted, that in perception the mind acts upon the object, or the object upon the mind, and, at the same time, admit the truth of the maxim, that "nothing can act but where it is," we must, of necessity conclude, either that objects are perceived in a way similar to what is supposed in the ideal theory, or that, in every act of perception, the soul quits the body, and is present to the object perceived. And accordingly, this alternative is expressly stated by Malebranche; who differs, however, from the writer last quoted, in the choice which he makes of his hypothesis; and even rests his proof of its truth on the improbability of the other opinion. "I suppose," says he, "that every one will grant, that we perceive not external objects immediately, and of themselves. We see the sun, the stars, and an infinity of objects without us; and it is not at all likely that, upon such occasions, the soul sallies out of the body in order to be present to the objects perceived. She sees them not therefore by themselves; and the immediate object of the mind is not the thing perceived, but something which is intimately united to the soul; and it is that which I call an idea: so that by the word idea, I understand nothing else here but that which is nearest to the mind when we perceive any object. It ought to be carefully observed, that, in order to the mind's perceiving any object, it is absolutely necessary that the ideas of that object be actually present to it. Of this it is not possible to doubt. The things which the soul perceives, are of two kinds. They are either in the soul, or they are without the soul. Those that are in the soul, are its own thoughts; that is to say, all its different modifications. need of ideas for perceiving these things. But with regard to things without the soul, we cannot perceive them but by means of ideas." The soul has no All these theories appear to me to have taken their rise, first, from an inattention to the proper object of philosophy, and, secondly, from an apprehension, that we understand the connection between impulse and motion better than any other physical fact. From the detail which I have given, it appears how extensive an influence this prejudice has had on the inquiries both of natural philosophers and of metaphysicians. II. Of Dr. Reid's Speculations on the subject of Perception.—It was chiefly in consequence of the skeptical 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 shown, 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 statement 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. Useful effect of plain truth in reminding us of our ignorance, and reviving our natural feelings. — 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 |