Nor is it only to account for the connexion be. tween the object and the organ of fenfe, that philofophers have had recourse to the theory of impulse. They have imagined that the impreffion on the organ of fenfe is communicated to the mind, in a fimilar manner. As one body produces a change in the state of another by impulfe, fo it has been supposed, that the external object produces perception, (which is a change in the state of the mind,) first, by fome material impreffion made on the organ of sense; and, fecondly, by fome material impreffion communicated from the organ to the mind along the nerves and brain. These fuppofitions, indeed, as I had occafion already to hint, were, in the ancient theories of perception, rather implied than expreffed; but by modern philosophers, they have been stated in the form of explicit propofitions. "As to the manner," fays Mr. Locke, “in "which bodies produce ideas in us, it is manifeftly

by impulfe, the only way which we can conceive "bodies operate in *." And Sir Ifaac 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 impulfe, fo no connexion could be carried on between matter and mind, unless the mind were prefent (as he expreffes it) to the matter from which the last impreffion is communicated. "Is not" (fays he) the fenforium of "animals, the place where the fentient fubftance is

prefent; 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

* Effay on Human Understanding, book ii. chap. viii. § 11. G

❝ in

"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 fame time, admit the truth of the maxim, that " nothing "can act but where it is," we muft, of neceffity, conclude, either that objects are perceived in a way fimilar to what is fuppofed in the ideal theory, or that, in every act of perception, the foul quits the body, and is present to the object perceived. And accordingly, this alternative is exprefsly ftated by Malebranche; who differs, however, from the writer laft quoted, in the choice which he makes of his hypothefis; and even refts his proof of its truth on the improbability of the other opinion. "I suppose," fays he," that every one will grant, that we perceive "not external objects immediately, and of them. "felves. We fee the fun, the ftars, and an infinity "of objects without us; and it is not at all likely "that, upon fuch occafions, the foul fallies out of the "body, in order to be present to the objects per"ceived. She fees them not therefore by themfelves; "and the immediate object of the mind is not the

thing perceived, but fomething which is intimately "united to the foul; and it is that which I call an "idea: fo that by the word idea, I underfland no

66

thing 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 abfolutely neceffary that "the idea of that object be actually prefent to it. Of

Ant. Met. vol. ii. p. 306.

❝ this

"this it is not poffible to doubt. The things which "the foul perceives, are of two kinds. They are "either in the foul, or they are without the foul. "Thofe that are in the foul, are its own thoughts; "that is to fay, all its different modifications. The "foul has no need of ideas for perceiving thefe things. "But with regard to things without the foul, we cannot perceive them but by means of ideas."

To thefe quotations, I fhall add another, which contains the opinion of Buffon upon the subject. As I do not understand it fo completely, as to be able to translate it in a manner intelligible to myself, I fhall transcribe it in the words of the author.

"L'ame s'unit intimement à tel objet qu'il luit 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 en un inftant . . . . la volonté n'eft-elle donc 'qu'un mouvement corporel, et la contemplation un

fimple attouchement? Comment cet attouchement "pourroit-il fe faire fur un objet éloigné, fur un fujet "abftrait? Comment pourroit-il s'opérer en un inftant "indivifible? A-t-on jamais conçu du mouvement, "fans qu'il y êut de l'efpace et du tems? La volonté, "fi c'est un mouvement, n'eft donc pas un mouve"ment matériel, et fi l'union de l'ame à son objet est "un attouchement, un contact, cet attouchement ne "fe fait-il pas au loin? ce contact n'eft il pas une pénétration ?"

All these theories appear to me to have taken rife, first, from an inattention to the proper object of philofophy, and an application of the fame general maxims to physical and to efficient causes; and, fecondly,

from an apprehenfion, that we understand the connexion between impulfe and motion, better than any other phyfical fact. From the detail which I have given, it appears how extenfive an influence this prejudice has had on the inquiries both of natural philofophers and of metaphysicians.

In the foregoing reasonings, I have taken for granted, that motion may be produced by impulse; and have contented myself with afferting, that this fact is not more explicable, than the motions which the Newtonians refer to gravitation; or than the intercourfe which is carried on between the mind and external objects in the cafe of perception. The truth, however, is, that fome of the ableft philofophers in Europe are now fatisfied, not only that there is no evidence of motion being in any cafe produced by the actual contact of two bodies; but that very strong proofs may be given, of the abfolute impoffibility of such a supposition and hence they have been led to conclude, that all the effects which are commonly referred to impulfe, arife from a power of repulfion, extending to a fmall and imperceptible distance round every element of matter. If this doctrine shall be confirmed by future fpeculations in physics, it must appear to be a curious circumstance in the hiftory of science, that philofophers have been fo long occupied in attempting to trace all the phenomena of matter, and even fome 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 obfervation with a view to depreciate the labours of these philofophers; for, although the system of Boscovich were completely esta

blished,

blished, it would not diminish, in the smallest degree, the value of those physical inquiries, which have proceeded on the common hypothefis, with refpect to impulfe. The laws which regulate the communication of motion, in the cafe of apparent contact, are the most general facts we obferve among the terreftrial 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 philofophers fhould begin their phyfical inquiries, with attempting to refer to these, (which are the most general laws of nature, expofed 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 refolve these laws into fome principle still more general, without affecting the folidity of the common doctrine, so far as it goes.

IT

SECTION III.

of Dr. Reid's Speculations on the Subject of Perception.

was chiefly in confequence of the sceptical conclufions which Bishop Berkeley and Mr. Hume had deduced from the ancient theories of perception, that Dr. Reid was led to call them in queftion; and he appears to me to have fhewn, in the most satisfactory manner, not only that they are perfectly hypothetical, but that the fuppofitions they involve, are abfurd and impoffible. His reafonings, on this part of our conftitution, undoubtedly form the most

G 4