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Nor is it only to account for the connexion be. tween the object and the organ of sense, that philofo. phers 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
As one body produces a change in the state of another by impulse, fo 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 *.” 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 impresion 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
* Essay on Human Understanding, book ii. chap. viii. s 11.
“ 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 them. “ felves. 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 foul sallies out of the
body, in order to be present to the objects per“ ceived. 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 : fo that by the word idea, I understand no
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 absolutely necessary that “the idea of that object be actually present to it. Of
* Ant. Met. vol. ii. p. 306.
“ this it is not possible to doubt. The things which " the foul 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 can
not 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 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 instant .... la volonté n'est-elle donc “ qu’un mouvement corporel, et la contemplation un “ simple attouchement ? Comment cet attouchement “ 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, “ fans qu'il y eut de l'espace et du tems ? La volonté, “ si c'est un mouvement, n'est donc pas un mouve“ment 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 rise, first, from an inattention to the proper object of phi. lofophy, and an application of the fame general maxims to physical and to efficient causes ; and, fecondly,
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 ableft 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 labours of these philosophers; for, although the system of Boscovich were completely esta
blished, 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 in. fancy. 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 folidity of the common doctrine, so far as it goes.
of Dr. Reid's Speculations on the Subject of Perception.
IT: was chiefly in consequence of the sceptical con
clusions 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 in. volve, are absurd and impossible. His reasonings, on this part of our constitution, undoubtedly form the