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philosopher' nowhere mentions it as a fact, nor does he build any thing upon it.
As there is, without doubt, an impression made upon the nerves and upon the brain in the act of perception, it has been an opinion very generally received among philosophers, that by means of the nerves and brain,' an impulse or impreffion is also made upon the mind. : This opinion the Author thews to be entirely groundless, and merely founded upon an imaginary analogy between body and mind. As one body acts upon another by making an impreffion upon it, it has been thought that the mind has come effect of a fimilar nature produced upon it by the object independently of its own activity. This is mere hypothesis ; the external object does not act, nor can it act. The perception of it is the operation of the percipient' being. Intorefting objects are indeed faid in common language to make impreffions on the mind, but it is in a figurative fignification. :
Ic has also been an opinion commonly received among philosophers, that the mind does not perceive external objects immediately; but that it perceives them by means of certain images of them conveyed to it by the senses.' The doctrine concerning images, as the immediate objects of perceptions probably had its origin in the fchool of Pythagoras. It was adopted by Ariftotle, and maintained by all his followers. It was likewise a part of the philosophy of Democritus and Epicurus, and it has found numerous supporters in succeeding ages. Des Cartes thought he had discovered the seat of the fout in the pineal gland, and supposed that in this fixed refidence the fits and receives intelligence of all objects that affect the senses. Others, withoot ventuting to determine the particular spot, have afligned a habitation, fenforium, or presence-room to the soul, somewhere in the brain. These opinions, that the soul has its seat in the brain, that there are images of all objects of sense formed in the brain, that these images are the mind's immediate objects of perception, and that external objects themselves are only perceived by means of them, are thewn by Dr: Reid to be mere fuppositions fupported by no sort of evidence or probability. One or more, however, of these groundless hypothesis is affuned as a truth to be taken for granted' in every account of perception that has been given by philosophers. It appears, particularly, to have been admitted as a fundamental maxim, ever fince the days of Pythagoras, Plato, and Aristotle, that the mind does not perceive things themselves, but only certain images, ideas, or impreslions of them in the brain, or upon the mind. In this general point they all agree, however they may have differed in explaining particulars.
In the fifth chapter of this Efay the Author treats of perception in general, and observes, that if we attend to that act of
our mind which we call the perception of an external obje&t of sense, we lball find it in these three things. Firft, Some conception or notion of the object perceived. Secondly, A ftrong and irresiftible convi&ion and belief of its present exiftence. And, thirdly, That this conviction and belief are immediate, and not the effect of reasoning.' It has not, however, been the common opinion of philosophers, that these three particulars are always to be found in this operation. The Author, therefore, takes occasion, in several subsequent chapters, to state and examine the sentiments of the moft eminent writers upon the human mind concerning the perception of external objects. The theory of Father Malebranche, the opinions of the ancient Peripatetics, and of Des Cartes, the do&rines of Mr. Locke, of Bishop Berkeley, of Mr. Hume, of Mr. Arnauld, and of Mr. Leibnitz, are brought fucceffively under review. In this part of the treatise, the Author discovers a perfect acquaintance with the labours of his predecessors in the same branch of inquiry. He has stated their opinions with fairness and perspicuity. He has examined them with candour, and bas pointed out the defects of them with great acuteness, and sometimes with good-humoured pleasantry. But, as we formerly observed, a general view of this part of the work can hardly be communicated by an abstrad, and therefore we must refer the inquisitive reader to the book itself.
In the fourteenth chapter several judicious reflections are made upon the commonly received philosophical theory, that the mind does not perceive nor remember things themselves, but only their ideas: and that it infers the existence of external objects from certain ideas or resemblances of them present with it self, which are the immediate objects of its thoughts. The reflections on this theory, which the Author illuftrates at confiderable length, are the following:
I, • It is directly contrary to the universal sense of men who have not been instructed in philosophy.' Such men arç fully persuaded that those things which are immediately per. ceived by the senses, are objects existing without them, and are not in their own minds. 2. • The authors who have treated of ideas have generally taken their existence for granted, as a thing that could not be called in question; and such arguments as they have mentioned incidentally, in order to prove it, seem too weak to support the conclusion.' In proof of this, the arguments of Mr. Locke, Mr. Norris, Dr. Clarke, Dr. Por terfield, and Mr. Hume, to prove the exiftence of ideas, are particularly examined. 3. • Philosophers, notwithfanding their unanimity as to the existence of ideas, hardly agree in any one thing else concerning them.' 4. Ideas do not make any of the operations of the mind to be better underfood, although it was
probably with that view that they have been first invented, and afterwards so generally received. In confirmation of this, it is shewn, that if we perceive diftant objects, remember things paft, and imagine things that do not exist, by means of ideas, these operations seem to be reduced to onę, to wit, a kind of feeling of things present, and in contact with the percipient. But this feeling is not explained by contact ; for two things may be in contact without feeling or perception. This theory, therefore, without explaining any thing, only tends to confound operations of the mind which all men know to be different. 5. 'The natural and necessary consequences of it furnish a juft prejudice againft it to every man who pays a due regard to the common fense of mankind.' In illustration of this reflection several philosophical paradoxes, founded on the theory of ideas, are ad duced. Plato imagined that we see only the shadows of things, and not the things themselves. The Peripatetics thought that we do not perceive objects, but only certain sensible species transmitted from them. Des Cartes, Malebranche, Arnauld, and Locke, thought it necessary to prove by philosophical arguments the existence of material objects. Berkeley denied the existence of an external world, and of abftract notions. Hume denied that there is either space or time, body or mind, or any thing else but impreffions and ideas; and, moreover, maintained that no one propofition is more probable than another. These and many more paradoxes are deduced by fair and conclusive reasoning from the theory of ideas, and ought to create a prejudice against it in the minds of sensible men.
Dr. Reid concludes his account of perception, and the theories concerning it, with the following observations :
• Such fuppofitions, while there is no proof of them offered, are nothing but the fiétions of human fancy; and we ought no more to believe them, than we believe Homer's fictions of Apollo's filver bow, or Minerva's field, or Venus's girdle. Such fictions in poetry are agreeable to the rules of the art : they are intended to please, not to convince. But the philosophers would have us to believe their fictions, though the account they give of the phænomena of nature has commonly no more probability than the account that Homer gives of the plague in the Grecian camp, from Apollo taking his Itation on a neighbouring mountain, and from his filver bow lets ting Ay his swift arrows into the camp.
Men then only begin to have a true taste in philosophy, when they have learned to hold hypotheses in just contempt, and to confider them as the reveries of speculative men, which will never have any fimilitude to the works of God.
The Supreme Being has given us fome intelligence of his works, by what oor senses inform us of external things, and by what our consciousness and reflection inform us concerning the operations of our own minds. Whatever can be inferred from these common ob. fervations, by just and sound reasoning, is true and legitimate phiR 3
lofophy: but what we add to this from conjecture is all spurious and illegitimate.
• After this long account of the theories advanced by philosophers, to account for our perception of external objects, I hope it will appear, that neither Aristotle's theory of sensible species, nor Malebranche's, of our seeing things in God, nor the common theory of our perceiving ideas in our own minds, nor Leibnitz's theory of monads and a pre-established harmony, give any fatisfying account of this power of the mind, nor make it more intelligible than it is without their aid. They are conjectures, and if they were true, would folve no difficulty, but raise many new ones. It is therefore more agreeable to good sense, and to found philosophy, to relt satisfied with what our consciousness and attentive reflection discover to us of the nature of perception, than by inventing hypotheses to attempt to explain things which are above the reach of human understanding. I believe no man is able to explain how we perceive external objects, any more than how we are conscious of those that are internal. Perception, consciousness, memory, and imagination, are all origical and simple powers of the mind, and parts of its conftitution, For this reason, though I have endeavoured to thew, that the theories of philosophers on this subject are ill-grounded and insufficient, I do not attempt to substitute any other theory in their place.
• Every man feels that perception gives him an invincible belief of the existence of that which he perceives; and that this belief is not the effect of reasoning, but the immediate consequence of perçeption. When philosophers have wearied themselves and their readers with their speculations upon this subject, they can neither itrengthen this belief nor weaken it; nor' can they show how it is produced. It puts the philosopher and the peasant upon a level; and neither of them can give any other reason for believing his senses, than that he finds ic impossible for him to do otherwise.'
After treating of perception, and the theories that bave been invented to account for it, the Author, in the fixteenth chapter, confiders sensation, which, by our conftitution, is conjoined with perception, and with many other acts of our minds, Having already inserted the Author's explanation of sensation, we fall here fubjoin a summary view of bis observations with regard to it.
Almost all our perceptions have corresponding fensations which constantly accompany them, and on that account are very apt to be confounded with them. In common language the lensation and its corresponding perception are not diftinguished, when the purposes of common life do not require it. Hence the quality perceived, and the sensation corresponding to that perception, often go under the same name. A fensation, in order to exift, must be feli, and has no object distinct from that act of mind by which it is felt. A perception, on the contrary, has always an external object that is perceived. 40 agreeable sensation of smell, for instance, may be felt without any thought of an odoriferous body being suggested to the mind, But perception may be conjoined with this lensation. We may
observe that the agreeable feeling is occafioned by the presence of some aromatic substance, and thence be led to conclude that there is some quality in that fubftance which is the cause of it. This quality may be perceived ; but cannot be an object of fenration. Both the external quality and the sensation are called the smell of a particular substance, though the one of them is truly in the object, and the other is in the fentient being. In the same manner I may feel heat, without thinking of any relation it has to fire, or any other external thing; in which case it is a mere fenfation; or I may perceive that the sensation is occafioned by some quality in the fire. I say indifferently that the heat is in me, or that it is in the fire ; but in these iwo applications I use the term beat in different senses. The sensation and ihe quality both in reality exist, but the former is the sign, and the latter the thing signified: and according to the nature of circumstances, either of them may become so much the object of attention, that the other shall be disregarded by the mind. The case is fimilar when sensacions accompany our desires. In every appetite and affection there is an agreeable or disagreeable -sensation, as well as a desire : and from the attention having been chiefly fixed upon one or other of the ingredients, these principles have been sometimes denominated delires, and sometimes sersations or feelings. Besides those sensations which are agreeable or painful, there are many that are indifferens, and that generally pass unnoticed. As the perception and tenfation are always conjoined, they coalesce in the imagination, and are apt to be considered as one simple operation, and are usually denoted by the same common name. They ought, however, 10 be diftinguilhed: Sensation implies neither the perception nor belief of any external object; but perception implies both conception and belief of something different from the percipient mind and the act of perception. The want of this distinction Dr. Reid reprefents as having given occasion to most of the false theories of philofophers with regard to the tenses. They have comprehended both sensation and percept. 'n under the same name, and considered them as one uncompounded operation. Hence they have called all our notions of material otjects ideas of sensation. Mr. Locke saw that the sensations excited by what are called secondary qualities have no retemblance to any thing that pertains to body; and hence concluded, that colour, and imell, and taste, and heat, and hardness, and the like, do not exilt in the object, but are niere ideas in the mind. Dr. Berkeley perceived that the same observation is applicable to primary qualities, and that our sensations resemble no material object whatever. Hence, taking it for granted that the senses present nothing to the mind but sensations, he concluded that there is no material world. • If the fenfes,' Dr. Reid obferves, furR 4