observed, first, That we know that such vibrations do really exist; and, secondly, That they tally exactly with the most remarkable phænomena of sound. We cannot, indeed, shew how any vibration should produce the sensation of sound. This must be resolved into the will of God, or into some cause altogether unknown. But we know that, as the vibration is strong or weak, the sound is loud or low; we know that, as the vibration is quick or slow, the sound is acute or grave. We can point out that relation of synchronous vibrations which produces harmony or discord, and that relation of successive vibrations which produces melody; and all this is not conjectured, but proved by a sufficient induction. This account of sounds, therefore, is philosophical: although, perhaps, there may be many things relating to sound that we cannot account for, and of which the causes remain latent. The connections described [94] in this branch of philosophy are the work of God, and not the fancy of men. If anything similar to this could be shewn in accounting for all our sensations by vibrations in the medullary substance of the nerves and brain, it would deserve a place in sound philosophy; but, when we are told of vibrations in a substance which no man could ever prove to have vibrations, or to be capable of them; when such imaginary vibrations are brought to account for all our sensations, though we can perceive no correspondence in their variety of kind and degree to the variety of sensations-the connections described in such a system are the creatures of human imagination, not the work of God. The rays of light make an impression upon the optic nerves; but they make none upon the auditory or olfactory. The vibrations of the air make an impression upon the auditory nerves; but none upon the optic or the olfactory. The effluvia of bodies make an impression upon the olfactory nerves; but make none upon the optic or auditory. No man has been able to give a shadow of reason for this. While this is the case, is it not better to confess our ignorance of the nature of those impressions made upon the nerves and brain in perception, than to flatter our pride with the conceit of knowledge which we have not, and to adulterate philosophy with the spurious brood of hypotheses ?* Reid appears to have been unacquainted with the works and theory of Bonnet.-With our author's strictures on the physiological hypotheses, the reader may compare those of Tetens, in his "Versuche." and of Stewart in his "Philosophical Essays."-H. SOME philosophers among 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 [95] 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 our 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 perception. But no reasoning is more fallacious than this-that, because two things are always conjoined, therefore one must be the cause of the other. Day and night have been joined in a constant succession since the beginning of the world; but who is so foolish as to conclude from this that day is the cause of night, or night the cause of the following day? There is indeed nothing more ridiculous than to imagine that any motion or modification of matter should produce thought. If one should tell of a telescope so exactly made as to have the power of seeing; of a whispering gallery that had 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 was 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. Passing this, therefore, as a notion too absurd to admit of reasoning, another conclusion very generally made by philosophers is, that, in perception, an impression is made upon the mind as well as upon the organ, nerves, and brain. Aristotle, as was before observed, thought that the form or image of the object perceived, enters by *The Stoics are reprehended for such a doctrine by Boethius: "Quondam porticus attulit The tabula rasa remounts, however, to Aristotle -indeed to Plato-as an illustration.-H. the organ of sense, and strikes upon the mind. Mr Hume gives the name of impressions to all our perceptions, to all our sensations, and even to the objects which we perceive. Mr Locke affirms very positively, that the ideas of external objects are produced [96] in our minds by impulse, "that being the only way we can conceive bodies to operate in." It ought, however, to be observed, in justice to Mr Locke, that he retracted this notion in his first letter to the Bishop of Worcester, and promised, in the next edition of his Essay, to have that passage rectified; but, either from forgetfulness in the author, or negligence in the printer, the passage remains in all the subsequent editions I have seen. There is no prejudice more natural to man than to conceive of the mind as having some similitude to body in its operations. Hence men have been prone to imagine that, as bodies are put in motion by some impulse or impression made upon them by contiguous bodies, so the mind is made to think and to perceive by some impression made upon it, or some impulse given to it by contiguous objects. If we have such a notion of the mind as Homer had of his gods-who might be bruised or wounded with swords and spears-we may then understand what is meant by impressions made upon it by a body; but, if we conceive the mind to be immaterial-of which I think we have very strong proofs we shall find it difficult to affix a meaning to impressions made upon it. There is a figurative meaning of impressions on the mind which is well authorized, and of which we took notice in the observations made on that word; but this meaning applies only to objects that are interesting. To say that an object which I see with perfect indifference makes an impression upon my mind, is not, as I apprehend, good English. If philosophers mean no more but that I see the object, why should they invent an improper phrase to express what every man knows how to express in plain English? But it is evident, from the manner in which this phrase is used by modern philosophers, that they mean, not barely to express by it my perceiving an object, but to explain the manner of perception. They think that the object perceived acts upon the mind in some way similar to that in which one body acts upon another, by making [97] an impression upon it. The impression upon the mind is conceived to be something wherein the mind is altogether passive, and has some effect pro A mere metaphor in Aristotle. (See Notes K and M.) At any rate, the impression was supposed made on the animated sensory, and not on the -H. duced in it by the object. But this is a hypothesis which contradicts the common sense of mankind, and which ought not to be admitted without proof. When I look upon the wall of my room, the wall does not act at all, nor is capable of acting; the perceiving it is an act or That this is the common operation in me. apprehension of mankind with regard to perception, is evident from the manner of expressing it in all languages. The vulgar give themselves no trouble how they perceive objects-they express what they are conscious of, and they express it with propriety; but philosophers have an avidity to know how we perceive objects; and, conceiving some similitude between a body that is put in motion, and a mind that is made to perceive, they are led to think that, as the body must receive some impulse to make it move, so the mind must receive some impulse or impression to make it perceive. This analogy seems to be confirmed, by observing that we perceive objects only when they make some impression upon the organs of sense, and upon the nerves and brain; but it ought to be observed, that such is the nature of body that it cannot change its state, but by some force impressed upon it. This is not the nature of mind. All that we know about it shews it to be in its nature living and active, and to have the power of perception in its constitution, but still within those limits to which it is confined by the laws of Nature. It appears, therefore, that this phrase of the mind's having impressions made upon it by corporeal objects in perception, either a phrase without any distinct meaning, and contrary to the propriety of the English language, or it is grounded upon an hypothesis which is destitute of proof. On that account, though we grant that in perception there is an impression made upon the organ of [98] sense, and upon the nerves and brain, we do not admit that the object makes any impression upon the mind. There is another conclusion drawn from the impressions made upon the brain in perception, which I conceive to have no solid foundation, though it has been adopted very generally by philosophers. It is, that, by the impressions made on the brain, images are formed of the object perceived; and that the mind, being seated in the brain as its chamber of presence, immediately perceives those images only, and has no perception of the external object but by them. This notion of our perceiving external objects, not immediately, but in certain images or species of them conveyed by the senses, seems to be the most ancient philosophical hypothesis we have on the subject of perception, and to have with small variations retained its authority to Aristotle, as was before observed, main- Aristotle thought every object of human understanding enters at first by the senses;* and that the notions got by them are by the powers of the mind refined and spiritualized, so as at last to become objects of the most sublime and abstracted sciences. Plato, on the other hand, had a very mean opinion of all the knowledge we get by the senses. He thought it did not deserve the name of knowledge, and could not be the foundation of science; because the objects of sense are individuals only, and are in a constant fluctuation. All science, according to him, must be employed about those eternal and immutable ideas which existed before the objects of sense, and are not liable to any change. In this there was an essential difference between the systems of these two philosophers. [99] The notion of eternal and immutable ideas, which Plato borrowed from the Pythagorean school, was totally rejected by Aristotle, who held it as a maxim, that there is nothing in the intellect, which was not at first in the senses. But, notwithstanding this great difference in those two ancient systems, they might both agree as to the manner in which we perceive objects by our senses: and that they did so, I think, is probable; because Aristotle, as far as I know, neither takes notice of any difference between himself and his master upon this point, nor lays claim to his theory of the manner of our perceiving objects as his own invention. It is still more probable, from the hints which Plato gives in the seventh book of his Republic, concerning the manner in which we perceive the objects of sense; which he compares to persons in a deep and dark cave, who see not external objects themselves but only their shadows, by a light let into the cave through a small opening.+. are perceived only by certain images, or shadows of them, let into the mind, as into a camera obscura.• The notions of the ancients were very various with regard to the seat of the soul Since it has been discovered, by the improvements in anatomy, that the nerves are the instruments of perception, and of the sensations accompanying it, and that the nerves ultimately terminate in the brain, it has been the general opinion of philosophers that the brain is the seat of the soul; and that she perceives the images that are brought there, and external things, only by means of them. Des Cartes, observing that the pineal gland is the only part of the brain that is single, all the other parts being double,+ and thinking that the soul must have one seat, was determined by this [100] to make that gland the soul's habitation, to which, by means of the animal spirits, intelligence is brought of all objects that affect the senses.§ Others have not thought proper to confine the habitation of the soul to the pineal gland, but to the brain in general, or to some part of it, which they call the sensorium. Even the great Newton favoured this opinion, though he proposes it only as a query, with that modesty which distinguished him no less than his great genius. "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? And is there not an incorporeal, living, intelligent, and omnipresent Being, who, in infinite space, as if it were in his sensorium, intimately perceives things themselves, and comprehends them perfectly, as being present to them; of which things, that principle in us, which perceives and thinks, discerns only, in its little sensorium, the images brought to it through the organs of the senses?"|| His great friend Dr Samuel Clarke adopted the same sentiment with more confidence. In his papers to Leibnitz, we find the following passages: "Without being present to the images of the things It seems, therefore, probable that the Py-perceived, it (the soul) could not possibly thagoreans and Platonists agreed with the Peripatetics in this general theory of perception to wit, that the objects of sense This is a very doubtful point, and has accordingly divided his followers. Texts can be quoted to prove, on the one side, that Aristotle derived all our notions, a posteriori, from the experience of sense; and, on the other, that he viewed sense only as afford. ing to intellect the condition requisite for it to be. come actually conscious of the native and necessary notions it, a priori, virtually possessed.-H. t Reid wholly mistakes the meaning of Plato's simile of the cave. See below, under p. 116.-H, perceive them. A living substance can An error. See below, under p. 116.-H. See above, p. 234, b, note .-H. Before Reid, these crude conjectures of Newton were justly censured by Genovesi, and others, H, or to the images of things, (as the soul of man is in its proper sensory.) Nothing can any more act, or be acted upon, where it is not present, than it can be where it is not. We are sure the soul cannot perceive what it is not present to, because nothing can act, or be acted upon, where it is not. Mr Locke expresses himself so upon this point, that, for the [101] most part, one would imagine that he thought that the ideas, or images of things, which he believed to be the immediate objects of perception, are impressions upon the mind itself; yet, in some passages, he rather places them in the brain, and makes them to be perceived by the mind there present. "There are some ideas," says he," which have admittance only through one sense; and, if the organs or the nerves, which are the conduits to convey them from without to their audience in the brain, the mind's presence room, if I may so call it, are so disordered as not to perform their function, they have no postern to be admitted by. "There seems to be a constant decay of all our ideas, even of those that are struck deepest. The pictures drawn in our minds are laid in fading colours. Whether the temper of the brain makes this difference, that in some it retains the characters drawn on it like marble, in others like freestone, and in others little better than sand, I shall not enquire.' From these passages of Mr Locke, and others of a like nature, it is plain that he thought that there are images of external objects conveyed to the brain. But whether he thought with Des Cartest and Newton, that the images in the brain are perceived by the mind there present, or that they are imprinted on the mind itself, is not so evident. Now, with regard to this hypothesis, there are three things that deserve to be considered, because the hypothesis leans upon them; and, if any one of them fail, it must fall to the ground. The first is, That the soul has its seat, or, as Mr Locke calls it, its presence room in the brain. The second, That there are images formed in the brain of all the objects of sense. The third, That the mind or soul perceives these images in the brain; and that it perceives not external objects immediately, but only perceives them by means of those images. [102] As to the first point-that the soul has its No great stress should be laid on such figurative passages as indications of the real opinion of Locke, which, on this point, it is not easy to discover. See Note 0.-H. + Des Cartes is perhaps an erratum for Dr Clarke. If not, the opinion of Des Cartes is misrepresented; for he denied to the mind a'l consciousness or immediate knowledge of matter and its modifications. But of this again, See Note M.-H. seat in the brain-this, surely, is not so well established as that we can safely build other principles upon it. There have been various opinions and much disputation about the place of spirits: whether they have a place? and, if they have, how they occupy that place? After men had fought in the dark about those points for ages, the wiser part seem to have left off disputing about them, as matters beyond the reach of the human faculties. As to the second point-that images of all the objects of sense are formed in the brainwe may venture to affirm that there is no proof nor probability of this, with regard to any of the objects of sense; and that, with regard to the greater part of them, it is words without any meaning." We have not the least evidence that the image of any external object is formed in the brain. The brain has been dissected times innumerable by the nicest anatomists; every part of it examined by the naked eye, and with the help of microscopes; but no vestige of an image of any external object was ever found. The brain seems to be the most improper substance that can be imagined for receiving or retaining images, being a soft, moist, medullary substance. But how are these images formed? or whence do they come? Says Mr Locke, the organs of sense and nerves convey them from without. This is just the Aristotelian hypothesis of sensible species, which modern philosophers have been at great pains to refute, and which must be acknowledged to be one of the most unintelligible parts of the Peripatetic system. Those who consider species of colour, figure, sound, and smell, coming from the object, and entering by the organs of sense, as a part of the scholastic jargon long ago discarded from sound philosophy, ought to have discarded images in the brain along with them. There never was a shadow of argument brought by any author, to shew that an [103] image of any external object ever entered by any of the organs of sense. That external objects make some impression on the organs of sense, and by them on the nerves and brain, is granted; but that those impressions resemble the objects they are made by, so as that they may be called images of the objects, is most improbable. Every hypothesis that has been contrived, shews that there can be no such resemblance; for neither the motions of animal spirits, nor the vibrations of elastic chords, or of elastic æther, or of the infinites It would be rash to assume that, because a philosopher uses the term image, or impression, or idea, and places what it denotes in the brain, that be therefore means that the mind was cognizant of such corporeal affection, as of its object, either in percep. tion or imagination. See Note K.-H. FALSE CONCLUSIONS, &c. imal particles of the nerves, can be sup- We know that, in vision, an image of the It is farther to be observed, that, with regard to some objects of sense, we may understand what is meant by an image of them imprinted on the brain; but, with regard to most objects of sense, the phrase is absolutely unintelligible, and conveys no meaning at all. understand what is meant by an image of As to objects of sight, I their figure in the brain. But how shall we conceive an image of their colour where there is absolute darkness? And as to all other objects of sense, except figure and colour, 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. applied to these objects of sense, has absoThe word image, when lutely no meaning. Upon what a weak foundation, then, does this hypothesis stand, when it supposes that images of all the objects of sense are imprinted on the brain, being conveyed thither by the conduits of the organs and nerves! [104] The third point in this hypothesis is, That the mind perceives the images in the brain, and external objects only by means of them. This is as improbable as that there are such images to be perceived. If our powers of perception be not altogether fallacious, the objects we perceive are not in our brain, but without us. We are so far from perceiving images in the brain, that we do not perceive our brain at all; nor would any man ever have known that he had a brain, if anatomy had not discovered, by dissection, that the brain is a constituent part of the human body. To sum up what has been said with regard to the organs of perception, and the impressions made upon our nerves and brain. It is a law of our nature, established by the will of the Supreme Being, that we perceive no external object but by 257 pose. means of the organs given us for that purnot. But these organs do not perceive. sight. The eye is a natural organ of sight, The eye is the organ of sight, but it sees but it sees as little as the telescope. We A telescope is an artificial organ of visible object upon the retina; but how this know how the eye forms a picture of the picture makes us see the object we know not; and if experience had not informed us that such a picture is necessary to vision, give no reason why the picture on the rewe should never have known it. tina should be followed by vision, while a like picture on any other part of the body produces nothing like vision. We can It is likewise a law of our nature, that we organ, and by means of the organ upon the impressions be made by the object upon the perceive not external objects, unless certain those impressions we are perfectly ignorant; nerves and brain. But of the nature of and though they are conjoined with perception by the will of our Maker, yet it does nection with it in their own nature, far less not appear that they have any necessary conthat they can be the proper efficient cause of it. [105] We perceive, because God has because we have impressions from objects. given us the power of perceiving, and not sions, because our Maker has limited and We perceive nothing without those imprescircumscribed our powers of perception, by such laws of Nature as to his wisdom seemed meet, and such as suited our rank in his creation. * The doctrine of Reid and Stewart, in regard to our perception of external things, bears a close anatheory of assistance with that of physical influence. of occasional causes. most completely with the opinion of Ruardus Andala, It seems, however, to coincide a Dutch Cartesian, who attempted to reconcile the "Statuo," he says, "nos clarissimam et distinctissimam modo, quod omnino facere oportet, ad Deum, caushujus operationis et unionis posse habere ideam, si beneplacito admirandum hunc effectum derivemus. sam ejus primam et liberam ascendamus, et ab ejus Nos possumus huic vel illi motui e. gr. campanæ, sic et hederæ suspense, literis scriptis, verbis quibuscunque pronunciatis, aliisque signis, varias ideas alligare, ita, ut per visum, vel auditum in mente ex. citentur variæ ideæ, perceptiones et sensationes: annon hinc clare et facile intelligimus, Deum crea torem mentis et corporis potuisse instituere et ordi rare, ut per varios in corpore motus variæ in mente excitentur ideæ et perceptiones; et vicissim, ut per varias mentis volitiones, varii in corpore excitentur et producantur metus ? Hinc et pro varia alter logy to the Cartesian scheme of divine assistance, or effectum esse, a posteriori, continua, certissima et clarissima experientia docet. quibus modo fuit actum. omnique exceptione majores reciproci hujus commercii, operationis mentis in corpus, et corporis in mentem, nec non communionis status, sunt sensus omnes tum externi, tum interni; ut et omnes et singulæ et continuæ actiones mentis in corp 8, de tibus mentis ad proprietates corporis progredi velit, Si quis vero a proprietadeducere motum in corpore, & perceptiones in mente, aut ex natura diversissimarum harum substantiarum næ is frustra erit, nihil intelliget, perversissime įhi. aut hos effectus ut necessario connexos spectare; S |