doctrine been understood by them, is it possible it should never be mentioned in terms explicit and full, that no reasonings should be founded on it, no causes of diseases deduced from it? In a word, to im

prove our genius and our taste, we cannot read the ancients too much; but we must seek important ad. ditions to our knowledge, whether moral, political, or mathematical, among the moderns."

WE

E have seen with how little success philosophers have invented theories, in order to throw light upon the process of sensation; and to trace the particular manner in which material objects convey impressions to our intellectual principle. They have not been less desirous to investigate the mode of action of perception; but as this faculty is of a still more intellectual and refined nature, it is not to be supposed that their hypotheses have been attended with very fortunate results. Such hypotheses, however, have been very prevalent from the remotest antiquity; and, contrary to the general course of such things, have preserved a considerable uniformity, and been implicitly admitted by succeeding philosophers as a rational basis of investigation. The consequence has been, a systematic diffusion of error in this branch of science, unparalleled in any other; so as at length to be matured into a complete system of scepticism, or disbelief. Those who wish to see the gradual progress of this sceptical philosophy completely developed, are referred to Dr. Reid's Second Essay on the Intellectual Powers. Our present plan requires only a brief statement of the leading opinions of philosophers concerning the operation of perception.

"The first philosopher, in whose writings we find a systematic theory concerning perception, is Aristotle. According to this theory, percep tion, as well as all the other operations of the mind, is carried on by the agency of certain images, forms, or species of material objects there present. The images presented to our senses were called sensible species, or forms; and were supposed to be continually sent off from material objects, in all directions; `so that by entering at the avenue of the senses, they produced perception during the day, and dreaming during the night. These images were supposed to be again presented to the memory, or imagination, in a more refined state, when they were called species, simply; and when presented to the intellect in their most refined state of all, they were called phantasms; and it was maintained, that there can be no perception, memory, or intellection, without species, or phantasms.

"This theory was well adapted to the Peripatetic philosophy, which resolved all the phenomena of the material world into the effects of two principles, called matter and form. It does not, however, appear to have originated with Aristotle ; for the followers of Democritus and Epicurus held a similar doctrine 04.

with

with regard to slender films of subtile matter, which they supposed to come from external objects. It is likewise probable that the Pythiagoreans and Platonists taught a similar theory of perception; as may be gathered 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 the situation of persons in a deep and dark cave, who see not external objects theinselves, but only their shadows, by a light let into the cave through a small opening.

"The principal difference among these sects, was concerning the origin of the objects of the human understanding. According to the Peripatetics, these must all enter originally by the senses, as sensible species, and are merely refined and rendered more spiritual by the intellectual faculties. This doctrine afterwards passed into the maxim, Nihil est in intellectu quod non fuit prius in sensu. Plato, on the other hand, had a very mean opinion of all the knowledge we get by the senses. All science, according to him, must be employed about what he called ideas, which are the eternal and immutable patterns of things, which existed before the objects of sense themselves, and are not liable to any change. This doctrine nearly coincides with what the Pythagoreans taught concerning their numbers.

"The Peripatetic philosophy, as is well known, continued to prevail in the world during a period of several centuries; nor were its metaphysical doctrines successfully opposed till the time of Descartes. The theory of perception, above detailed, received a considerable modification from this philosopher.

He did not, however, totally reject it; for he held it as certain, that it is only a representative picture, form, or species of an object, that is present in the mind when we perceive, and not the object itself. But he denied that these forms, or species, are sent forth from external bodies; and shewed the absurdity of this doctrine by solid arguments. He also gave the name of ideas to the representative forms which he supposed to be present in the mind; a term which he seems to have borrowed from the philosophy of Plato. Another peculiarity in the Cartesian system, was the origin which it assigned to certain of our ideas, such as those of time, space, motion, &c.; which it represented to be innate, or coeval with the mind itself.

"The Cartesian theory of percep tion was variously modified by Malebranche, and other succeeding metaphysicians: but it is not necessary, here, to specify the peculiar notions of each. The writings of Mr. Locke are justly entitled to more consideration than those of any philosopher of the period in question. It does not appear that his opinions, concerning perception, differed materially from those of Descartes; except in respect of the origin which he assigned to the representative images, or ideas, as they now were universally named. In this respect he differed both from the Peripatetics and Cartesians; and assigned all our ideas, or notions, to two sources, viz. 1st, sensation; and, 2d, reflection or consciousness, as we have already had occasion to specify.

"It is an evident consequence of the doctrine of perception, as admitted by Descartesand Mr. Locke, that we have no direct evidence for the existence of external objects, or

of

of a material world; since all the objects of our perception and consciousness are only ideas, or images, which have no dependence what ever upon external things. Both philosophers were too acute not to perceive this inference; but neither were inclined to give up the existence of a material world, although we have found them, with out reluctance, relinquishing the independent existence of the secondary qualities of body. The arguments, however, by which they endeavoured to establish the real existence of matter, are not very strong, and founded chiefly upon this position, that a benevolent Supreme power would never have given us faculties like the senses, merely in order to deceive us.

"But although we find Descartes and Mr. Locke conceiving that the existence of a material world is only supported by probable arguments, we are scarcely prepared for a system so repugnant to common sense, as positively and seriously to deny the existence of any kind of matter whatever. Yet such was the system of the ingenious bishop Berkeley, who was consider ed as one of the most philosophical reasoners of his day. The denial of the existence of the secondary qualities of body, but as mere sensations of the mind, which we have seen formed a part of the systems of Descartes and Locke, no doubt prepared the way for this sceptical doctrine; and it was not difficult to extend the arguments, by which the non-existence of the secondary qualities of body was supposed to be proved, to the primary also. ☛These, according to the prevailing theory of perception, were mere ideas or images present in the mind; and we know nothing of them but as ideas existing in the mind; so

that of the existence of external bodies we have no evidence. Berke ley states his system as a thing very obvious, and readily to be admitted.

Some truths there are,' says he, so near and obvious to the mind, that a man need only open his eyes to see them. Such I take this important one to be, that all the choir of heaven, and furniture of earth,-in a word, all those bodies which compose the mighty frame of the world, have not any subsistence without a mind.'

"Berkeley, though he denies the existence of a material world, yet, as became his cloth, decidedly espouses the existence of a world of spirits. In order to this, he admits that there are certain objects of human knowledge, which are not ideas, but things which have a permanent existence. These are our own minds, and their various operations, other finite minds, and the Supreme mind. And this he thinks must follow from the very nature of ideas, which, being inert, passive, unthinking beings, cannot be the images of thinking and active beings; of those very beings in which they exist.

"It was a large stride in scep ticism to deny the existence of a material worid: but the tenets soon after advanced by Mr. Hume, and grounded upon the same theory of our perceptions, go far beyond this, even to deny the existence of mind, as well as matter. This philosopher distinguishes the images, or pictures, which were supposed to be the obiects of our thoughts, into two classes, which he calls impressions and ideas; and comprehends under the first, all our sensations, passions, and emo◄ tions; and, under the last, the fainter copies of these, when we remember, imagine, or reason con

cerning

cerving them. He sets out with this as a principle that needed no proof, (and of which, therefore, he offers none), that all the percep tions of the human mind resolve themselves into these impressions and ideas. This being granted, it was easy to shew, by the same process which Berkeley employed to prove the non-existence of matter, that there is neither matter nor mind in the universe; nothing but impressions and ideas. What we call a body, is only a bundle of sensations; and what we call the ind, is only a bundle of passions, thoughts, and emotions, without any subject: so that Mr. Hume does not leave us even a self to claim the property of these impressions and ideas.

"The system of Mr. Hume is not to be considered as a mere philosophical reverie, concerning the manner in which the operations of the mind are conducted; but as a highly dangerous and insidious attempt to overturn every principle of belief, and rule of conduct. For it admits no other standard by which our opinions and reasonings are to be guided, than those hypothetical impressions, or ideas, which we are to look for within ourselves. From this singular assumption, the author endeavours logically to deduce, that there is no such thing as power, or intelligence, in the universe; no active cause, or voluntary agent; no time or space, matter or mind: in fine, that there is no such thing as evidence, or even probability; nor any reason why we should believe one thing, more than its contrary.

"Philosophical scepticism had now arrived at its utmost limits; and it became time to assert the privilege of reason, and examine upon what foundation doctrines of

so preposterous and dangerous a tendency rested. Dr. Reid has unquestionably the merit of being the first who successfully executed this task; and in his various works on the human mind, he has so completely accomplished it, as to leave little more to succeeding writers than to select and illustrate his various arguments.

"Onexamining the ground upon which the modern sceptical system rests, it is found to be nothing more than the hypothesis which represents all our perceptions and thoughts as carried on by means of images or representations of the thing perceived or thought of, present in the mind; which images, in modern times, have generally been called ideas; an hypothesis which, we have seen, has descended from a very high antiquity, under various modifications. As this theory was taught by the Peripatetics, however erroneous in its assumptions, it led to no sceptical conclusions; because it taught that the images present in the mind were sent forth by material objects; and, consequently, still left us the evidence of our senses for the existence of matter. But Descartes and his followers, while they retained the supposition of images in the mind, rejected that of their proceeding from the external body. The consequence was, that they began first with doubting the existence of material substances, and at length deliberately denied that there is any such thing in the world as matter, or mind, or any sentient being. It is pleasant,' says Dr. Reid, to observe, that while philosophers have so long been labouring, by means of ideas, to explain perception, and the other operations of the mind; those ideas have, by degrees, usurped

the

the place of perception, object, and even of the mind itself, and have supplanted those very things they were brought to explain.'

"It might be reasonably concluded, that this theory, which has so long prevailed in the world, and been so implicitly admitted as to sanction conclusions apparently the most absurd, rendered our notion of perception, as well as the other intellectual faculties, very clear and intelligible. This, however, is by no means the case; for, if we apply the theory to any other of the senses, except sight, it is altogether incomprehensible. I can indeed understand what is meant by an image or representation of visible forms or colours, because, I know that such images are painted on the retiua of the eye; and this fact seems to have afforded the origin of the whole hypothesis. But what is meant by the image or idea of a taste, of a smell, a sound, of sourness or sweetness, of loudness or lowness, of hardness or softness, I confess myself perfectly at a loss to determine. Much less can I pretend to understand what is meant by the images of intellectual objects, of truth or falsehood, fitness or unfitness, virtue or vice. Again, if we should ask, where are these images exhibited, and of what kind of materials are they formed? it would be difficult to obtain an answer from those who have most strenuously espoused the theory. It would seem, from the writings of Descartes, that he sometimes places the ideas of material objects in the brain, not only when they are perceived, but when they are remembered or imagined; but at other times he says, that we are not to conceive the images or traces in the brain to be perceived, as if there were eyes in the brain; these

traces being only occasions on which, by the laws of the union of soul and body, ideas are excited in the mind. Mr. Locke also seems to have wavered between these two opinions, sometimes representing the ideas of material things as being in the brain, but more frequently in the mind itself. Other philosophers, among whom we may rank Newton and Dr. Clarke, speak of the images of material things as being in that part of the brain called the sensorium, and perceived by the mind, there present: but Newton speaks of this point only incidentally, and, with his usual modesty, in the form of a query. As for Berkeley, his system leaves no brain on which the images could be traced; and the system of Mr. Hume leaves neither a brain nor a mind for the reception of his impressions and ideas.

"As to the particular nature or substance of the images, philosophers are generally silent. Mr. Locke indeed says, that our sen sations are produced in us by different degrees and modes of motion in our animal spirits, variously agitated by external objects: and again, that, by the faculties of memory and imagination, the mind has an ability, when it wills, to revive them again, and, as it were, to paint them anew upon itself, though some with more, some with less difficulty.' Dr. Robert Hook is almost the only author who is explicit on this subject. He informs us (Lect. on Light, sect. 7.) that ideas are completely material substances, and that the brain is furnished with a proper kind of matter for fabricating the ideas of each sense. The ideas of sight, he thinks, are formed of a kind of matter resembling the Bononian stone, or some kind of phosphorus ;

the