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the ancients, as well as among the moderns, imagined that man is nothing but a piece of matter so curiously organized, that the impressions of external objects produce in it sensation, perception, remembrance, and all the other operations we are conscious of. This foolish opinion could only take its rise, from observing the constant connection which the author of nature hath established between certain impressions made upon the senses, and our perception of the objects by which the impression is made; from which they weakly inferred that those impressions were the proper efficient causes of the corresponding perceptions. There is, indeed, nothing more ridiculous than to imagine that any motion or modification of matter should produce thought. If any one should tell of a telescope so exactly made as to have the power of seeing; of a whispering gallery so formed as to have the power of hearing; of a cabinet so nicely framed as to have the power of memory; or of a machine so delicate as to feel pain when it is touched; such absurdities are so shocking to common sense, that they would not find belief even among Savages. Yet it is the same absurdity to think that the impressions of external objects upon the machine of our bodies, can be the real efficient cause of thought and perception.” Perhaps never was there greater confusion of ideas than is discovered in this passage. We begin our strictures upon it by remarking, that it is consistent in Dr. Reid to deny that any action of the bodily organs can be the real efficient cause of perception; since according to his own principles before stated, matter cannot be the efficient cause of any thing; and of course he ought to deny that the several media which operate upon the senses, in smelling, tasting, seeing or hearing, can be the efficient cause of any action even in the nerves themselves; as, for instance, that light can be the efficient cause of the image upon the retina. But he does not choose to rest his objection upon this ground. He endeavours to confound with materialists those who maintain, that the action of outward objects upon the senses, and through their instrumentality upon the mind, may be the efficient cause of perception. Now surely his ideas must be confused, indeed, who does not perceive that there is no connection between this doctrine and materialism. Can any one deny that the mind and body reciprocally act upon each other? What are the mysterious ties that unite them, and what is the mode by which they operate upon one another, the deepest philosophy has never been able to ascertain; but nothing can be more certain than the fact, that they do produce effects upon each other, sometimes the body upon the mind, and at other times the mind upon the body. When a sword cuts the body, does it not cause pain in the mind, and is not the sword the efficient cause of that pain, operating upon the sentient principle within through the instrumentality of the external organs of sense? Where then is the difficulty in supposing that the rays of light acting upon the nervous coat of the eye and brain, are the efficient cause of vision? Dr. Reid has been guilty in this statement of a most egregious blunder. He makes materialism, or what is equivalent to materialism, to consist in maintaining that the action of outward objects upon the senses and through them upon the mind, is the efficient cause of thought, whereas it really consists in making thought the result of that action upon the bodily organs alone. The essence of materialism lies in making all our perceptions, thoughts and feelings, mere modes of motion, in the different bodily organs. The doctrine, however, of Mr. Locke and the best Philosophers, is not, as the Dr. says, that any motion or modification of matter can, of itself, without being connected with an immaterial principle, produce thought; for they concur in the opinion that if it be not as is asserted ridiculous, it is at any rate inconceivable; but that the soul and body being intimately united together, sympathise in all the alterations and modifications of each other; mutually act and re-act upon one another; at one time the one as a cause producing an effect upon the other, and vice versa. As to the manner or modus operandi in which they produce these effects, we are entirely in the dark, and likely ever to remain so. But is not the manner in which the intelligent principle within produces any effects upon the body equally as unsearchable, and even inconceivable, as the manner in which the body can operate upon the soul? A man receives a wound in his limb which gives pain to his mind; a delicate woman receives intelligence of the sudden death of a friend, and faints away; now, is there any more difficulty in our conceiving of the violence done to the outward organs as conveying pain to the mind by a mysterious action upon it, than that the sudden emotion of grief, which is a sentiment of the mind, should produce such a relaxation of the muscles of the body and remission of the functions of the whole system, as to occasion a person to faint? Yet the Dr. says, “it is the same absurdity to suppose, that the impressions of external objects upon the senses and through them upon the mind, are the efficient cause of perception, as to imagine a telescope so exactly made as to have the power of seeing, a whispering gallery that has the power of hearing, a cabinet so nicely framed as to have the power of memory, or a machine so delicate as to feel pain.” And yet he who thus confounds together things so evidently distinct, is the writer who has detected the errors and exposed the theory of that nicely discriminating mind and true light of science, the great metaphysiciar. of England! These are the errors and absurdities into which we are led by waterialism, but have nothing to do with the maxims of a sound and just philosophy.
Let us, now, state the argument upon which we ground the conclusion, that the several media which act upon the senses, and furnish us with our information concerning their several objects, are the real efficient causes of perceptions in the mind. “ This foolish opinion,” says Dr. Reid, “ could only have taken its rise from observing the constant connec
tion, which the author of nature hath established between certain impressions made upon the senses, and our perception of the objects by which the impression is made; from which they weakly inferred, that those impressions were the proper and efficient causes of the corresponding perception.” The foolish opinion, of which the Dr. speaks in the commencement of this sentence, was that of Aristotle, Des Cartes and Locke, all of whom considered the qualities of bodies as the causes of sensations in us. They did not draw this inference, however, solely from observing the constant connection established by the author of nature, between certain impressions made upon the senses and our perception of the objects by which such impressions are made; but from a thorough conviction resting upon facts, that besides the invariable connection between the presentation of an object to the senses and the correspondent perception, there must be a power in the cause adequate to produce the result. This inference they conceived themselves as not drawing weakly, but by as strong a cord of argument, as that by which they could, in any other case whatever, infer the cause from its effect. They knew nothing of that shallow philosophy, and idle jargon of words, which would resolve the whole relation of cause and effect into the constant contiguity and conjunction of objects; and make the whole business of natural science to consist, in tracing connections between signs and the things signified by them, introduced into the recent school of metaphysicks.
Let us, then, proceed to the consideration of the question, why we conclude, that the action of outward objects upon the senses and the organs of sense upon the mind, is the real and efficient cause of perception? The case would seem to be extremely clear and intelligible, if not embarrassed by metaphysical subtilty. There is not a single circumstance which can be mentioned, in any instance, that indicates the existence and agency of a cause which may not be recogni
zed in this. Take the example of vision by way of illustration, as every conclusion which can be deduced from nature as applicable to the one sense, will be found equally applicable to the others. We say that the rays of light passing from the object and converging towards a point, forming an image upon the retina, and producing an action in the nervous coat, and the brain, is the efficient cause of our seeing. The arguments, by which we prove this proposition, are, that unless an object is presented in a proper light and position, and the organs of vision be in a sound state, there is no perception; that in a good state of the organ and proper position of the object there is invariably vision; and moreover, to render the reasoning conclusive, they who are deprived of sight are entirely destitute of that assemblage of ideas obtained by the exercise of this sense.
Could we desire more satisfactory proof of any point than we have of this? What possible circumstances can in any case determine the existence of a cause which cannot be discovered here? Dr. Reid allows, that an image is always formed upon the retina by the rays of light, and that the formation of this image is necessary to distinct vision. Now, how can he prove that this image is invariably spread upon the retina, and that it is necessary to vision; but from the consideration, that whenever an object is presented to the organ in a proper light, the formation of this image is the necessary result, and that whenever this image is formed vision is the result? Constant conjunction and contiguity, although they by no means comprise the whole of our idea of the relation between cause and effect, certainly serve, for the most part, as a tolerably sure criterion by which to ascertain the existence of such relation between two objects. Now, it is evident that every argument which can be adduced to prove that the rays of light are the cause of the image formed at the bottom of the eye, may be made use of to prove also, that the action produced upon the nervous coat connected with the brain is the effi