man who has, in philosophical matters, a competent faculty of thinking, can ever fall into it." With this passage I so far agree, as to allow that it is impossible to conceive, in what manner one body acts on another at a distance, through a vacuum. But I cannot admit that it removes the difficulty to suppose, that the two bodies are in actual contact. That one body may be the efficient cause of the motion of another body placed at a distance from it, I do by no means assert; but only, that we have as good reason to believe that this may be possible, as to believe that any one natural event is the efficient cause of another. I have been led into this very long disquisition, concerning efficient and physical causes, in order to point out the origin of the common theories of perception; all of which appear to me, to have taken rise from the same prejudice, which I have already remarked to have had so extensive an influence upon the speculations of natural philosophers. 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 connexion 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 * Tum porro varios rerum sentimus odores, LUCRET. lib. i. p. 299, 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. 66 Nor is it only to account for the connexion 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."-Essay on Human Understanding, book ii. chap. viii. § II. And Sir Isaac Newton, although he does not speak of an impulse made on the mind, plainly proceeded on the principle that, as matter can only move matter by impulse, so no connexion could be carried on between matter and mind, unless the mind were present (as he expresses it) to the matter from which the last impression is communicated. "Is not," (says he) "the sensorium of animals, the place where the sentient substance is present? and to which the sensible species of things are brought, through the nerves and brain, that there they may be perceived by the mind present in that place?" 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 66 * This phrase of "the soul being present to the images of external objects," has been used by many philosophers, since the time of Des Cartes; evidently from a desire to avoid the absurdity of supposing, that images of extension and figure can exist in an unextended mind. "Quæris," (says Des Cartes himself, in replying to the objections of one of his antagonists,) "quomodo existimem in me subjecto inextenso recipi posse speciem, ideamve corporis quod extensum est. Respondeo nullam speciem corpoream in mente recipi, sed puram intellectionem tam rei corporeæ quam incorporeæ fieri absque ulla specie corporea; ad imaginationem vero, quæ non nisi de rebus corporeis esse potest, opus quidem esse specie quæ sit verum corpus, et ad quam mens se applicet, sed non quæ in mente recipiatur." It appears, therefore, that this philosopher supposed his images or ideas to exist in the brain, and not in the mind. Mr. Locke's expressions sometimes imply the one supposition, and sometimes the other. In his Treatise on the Eye. 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.' 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."-Ant. Met. vol. ii. p. 306. 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 * "The slightest philosophy," (says Mr. Hume,) "teaches us, that nothing can ever be present to the mind, but an image, or perception; and that the senses are only the inlets, through which these images are conveyed; without being able to produce any immediate intercourse between the mind and the object. The table, which we see, seems to diminish, as we remove farther from it: but the real table which exists independent of us, suffers no alteration: it was, therefore, nothing but its image which was present to the mind. "These," (he adds) "are the obvious dictates of reason."-Essay on the Academical or Skeptical Philosophy. 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. The soul has no need of ideas for perceiving these things. But with regard to things without the soul, we cannot perceive them but by means of ideas." To these quotations, I shall add another, which contains the opinion of Buffon upon the subject. As I do not understand it so completely, as to be able to translate it in a manner intelligible to myself, I shall transcribe it in the words of the author. "L'ame s'unit intimement à tel objet qu'il lui plâit, la distance, la grandeur, la figure, rien ne peut nuire à cette union lorsque l'ame la veut elle se fait et se fait et un instant. . . . la volonté n'est elle donc qu'un mouvement corporel, et la contemplation un simple attouchment? Comment cet attouchment pourroit-il se faire sur un objet éloigné, sur un sujet abstrait? Comment pourroit-il s'opérer en un instant indivisible? A-t-on jamais conçu du mouvement, sans qu'il y eût de l'espace et du tems? La volonté, si c'est un mouvement, n'est donc pas un mouvement matériel, et si l'union de l'ame à son objet est un attouchement, un contact, cet attouchement ne se fait-il pas au loin? ce contact n'est il pas une pénétration ?" All these theories appear to me to have taken their rise, first, from an inattention to the proper object of philosophy, and an application of the same general maxims to physical and to efficient causes, and, secondly, from an apprehension, that we understand the connexion 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. In the foregoing reasonings, I have taken for granted, that motion may be produced by impulse: and have contented myself with asserting, that this fact is not more explicable, than the motions which the Newtonians refer to gravitation; or than the intercourse which is carried on between the mind and external objects in the case of perception. The truth, however, is, that some of the ablest philosophers in Europe are now satisfied, not only that there is no evidence of motion being in any case produced by the actual contact of two bodies; but that very strong proofs may be given of the absolute impossibility of such a supposition; and hence they have been led to conclude, that all the effects which are commonly referred to impulse, arise from a power of repulsion, extending to a small and imperceptible distance round every element of matter.If this doctrine shall be confirmed by future speculations in physics, it must appear to be a curious circumstance in the history of science, that philosophers have been so long occupied in attempting to trace all the phenomena of matter, and even some of the phenomena of mind, to a general fact, which, upon an accurate examination, is found to have no existence. I do not make this observation with a view to depreciate the labors of these philosophers; for, although the system of Boscovich were completely established, it would not diminish, in the smallest degree, the value of those physical inquiries, which have proceeded on the common hypothesis, with respect to impulse. The laws which regulate the communication of motion in the 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. SECTION III. Of Dr. Reid's Speculations on the subject of Perception. Ir 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 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, |