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philofopher nowhere mentions it as a fact, nor does he build any thing upon it.

As there is, without doubt, an impreffion made upon the nerves and upon the brain in the act of perception, it has been an opinion very generally received among philofophers, that by means of the nerves and brain, an impulfe or impreffion is alfo made upon the mind. This opinion the Author fhews 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 fome effect of a fimilar nature produced upon it by the object independently of its own activity. This is mere hypothefis; the external object does not act, nor can it act. The perception of it is the operation of the percipient being. Interefting objects are indeed faid in common language to make impreffions on the mind, but it is in a figurative fignification.

It has also been an opinion commonly received among philo fophers, 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 fenfes. The doctrine concerning images, as the immediate objects of perception, probably had its origin in the fchool of Pythagoras. It was adopted by Ari ftotle, and maintained by all his followers. It was likewise a part of the philofophy of Democritus and Epicurus, and it has found numerous fupporters in fucceeding ages. Des Cartes thought he had difcovered the feat of the foul in the pineal gland, and fuppofed that in this fixed refidence fhe fits and receives intelligence of all objects that affect the fenfes. Others, without venturing to determine the particular fpot, have affigned a habitation, fenforium, or prefence-room to the foul, fomewhere in the brain. Thefe opinions, that the foul has its feat in the brain, that there are images of all objects of fenfe formed in the brain, that thefe images are the mind's immediate objects of perception, and that external objects themselves are only per ceived by means of them, are fhewn by Dr: Reid to be mere fuppofitions fupported by no fort of evidence or probability. One or more, however, of thefe groundless hypothefes is affumed as a truth to be taken for granted in every account of perception that has been given by philofophers. It appears, par ticularly, to have been admitted as a fundamental maxim, ever fince the days of Pythagoras, Plato, and Ariftotle, that the mind does not perceive things themselves, but only certain images, ideas, or impreflions 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 Effay the Author treats of perception in general, and obferves, that if we attend to that act of

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our mind which we call the perception of an external object of fenfe, we shall find it in these three things. Firft, Some conception or notion of the object perceived. Secondly, A ftrong and irrefiftible conviction and belief of its prefent 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 philofophers, that these three particulars are always to be found in this operation. The Author, therefore, takes occafion, in several subsequent chapters, to state and examine the fentiments 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 doctrines 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 difcovers a perfect acquaintance with the labours of his predeceffors in the fame branch of inquiry. He has ftated their opinions with fairness and perfpicuity. He has examined them with candour, and has pointed out the defects of them with great acuténefs, and fometimes with good-humoured pleasantry. But, as we formerly observed, a general view of this part of the work can hardly be communicated by an abstract, and therefore we muft refer the inquifitive reader to the book itself.

In the fourteenth chapter several judicious reflections are made upon the commonly received philofophical 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 itfelf, which are the immediate objects of its thoughts. The reflections on this theory, which the Author illuftrates at confiderable length, are the following:

1. It is directly contrary to the universal sense of men who have not been inftructed in philofophy.' Such men are fully perfuaded that those things which are immediately perceived by the fenfes, are objects exifting without them, and are not in their own minds. 2. The authors who have treated of ideas have generally taken their exiftence for granted, as a thing that could not be called in queftion; and fuch arguments as they have mentioned incidentally, in order to prove it, feem too weak to support the conclufion. In proof of this, the arguments of Mr. Locke, Mr. Norris, Dr. Clarke, Dr. Porterfield, and Mr. Hume, to prove the exiftence of ideas, are particularly examined. 3. Philofophers, notwithstanding their unanimity as to the exiftence 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 understood, although it was

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probably with that view that they have been firft invented, and afterwards fo generally received.' In confirmation of this, it is fhewn, that if we perceive distant objects, remember things paft, and imagine things that do not exift, by means of ideas, these operations seem to be reduced to one, to wit, a kind of feeling of things prefent, 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 neceffary confequences of it furnish a juft prejudice againft it to every man who pays a due regard to the common fenfe of mankind. In illuftration of this reflection several philofophical paradoxes, founded on the theory of ideas, are adduced. Plato imagined that we fee only the fhadows of things, and not the things themfelves. The Peripatetics thought that we do not perceive objects, but only certain fenfible fpecies tranfmitted from them. Des Cartes, Malebranche, Arnauld, and Locke, thought it neceffary to prove by philofophical arguments the exiftence 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 conclufive reasoning from the theory of ideas, and ought to create a prejudice against it in the minds of fenfible men.

Dr. Reid concludes his account of perception, and the theories concerning it, with the following obfervations:

Such fuppofitions, while there is no proof of them offered, are nothing but the fictions 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 fhield, 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 philofophers 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 ftation on a neighbouring mountain, and from his filver bow let ting fly his swift arrows into the camp.

Men then only begin to have a true tafte in philosophy, when they have learned to hold hypothefes in juft contempt, and to confider them as the reveries of fpeculative 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 our fenfes inform us of external things, and by what our confcioufnefs and reflection inform us concerning the operations of our own minds. Whatever can be inferred from these common obfervations, by just and found reasoning, is true and legitimate phi

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lofophy: but what we add to this from conjecture is all fpurious and illegitimate.

After this long account of the theories advanced by philofophers, to account for our perception of external objects, I hope it will appear, that neither Ariftotle's theory of fenfible fpecies, nor Malebranche's, of our feeing 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 dificulty, but raife many new ones. It is therefore more agreeable to good fenfe, and to found philofophy, to reft fatisfied with what our confcioufnefs and attentive reflection difcover to us of the nature of perception, than by inventing hypothefes 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 confcious of thofe that are internal. Perception, confcioufnefs, memory, and imagination, are all original and fimple powers of the mind, and parts of its conftitution. For this reafon, though I have endeavoured to fhew, that the theories of philofophers on this fubject are ill-grounded and infufficient, I do not attempt to fubftitute any other theory in their place.

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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 reafoning, but the immediate confequence of perception. When philofophers have wearied themselves and their readers with their fpeculations upon this fubject, they can neither ftrengthen this belief nor weaken it; nor can they fhow how it is produced. It puts the philofopher and the peafant upon a level and neither of them can give any other reafon for believing his fenfes, than that he finds it impoffible for him to do otherwise.?

After treating of perception, and the theories that have been invented to account for it, the Author, in the fixteenth chapter, confiders fenfation, which, by our conftitution, is conjoined with perception, and with many other acts of our minds. Having already inferted the Author's explanation of fenfation, we shall here fubjoin a fummary view of his obfervations with regard to it. Almost all our perceptions have correfponding fenfations which conftantly accompany them, and on that account are very apt to be confounded with them. In common language the fenfation and its corresponding perception are not diftinguished, when the purposes of common life do not require it. Hence the quality perceived, and the fenfation correfponding to that perception, often go under the fame name. A fenfation, in order to exift, must be felt, 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. An agreeable fenfation of fmell, for inftance, may be felt without any thought of an odoriferous body being fuggefted to the mind, But perception may be conjoined with this fenfation. We may obferve

obferve that the agreeable feeling is occafioned by the presence of fome aromatic fubftance, and thence be led to conclude that there is fome quality in that substance which is the cause of it. This quality may be perceived; but cannot be an object of fenfation. Both the external quality and the fenfation are called the smell of a particular fubftance, though the one of them is truly in the object, and the other is in the fentient being. In the fame 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 fenfation is occafioned by fome quality in the fire. I fay indifferently that the heat is in me, or that it is in the fire; but in these two applications I use the term beat in different fenfes. The fenfation and the quality both in reality exist, but the former is the fign, and the latter the thing fignified; and according to the nature of circumstances, either of them may become fo much the object of attention, that the other fhall be disregarded by the mind. The cafe is fimilar when fenfations accompany our defires. In every appetite and affection there is an agreeable or difagreeable fenfation, as well as a defire: and from the attention having been chiefly fixed upon one or other of the ingredients, these principles have been fometimes denominated defires, and fometimes fenfations or feelings. Befides thofe fenfations which are agreeable or painful, there are many that are indifferent, and that generally pafs unnoticed. As the perception and fenfation are always conjoined, they coalefce in the imagination, and are apt to be confidered as one fimple operation, and are ufually denoted by the fame common name. They ought, however, to be diftinguished: Senfation implies neither the perception nor belief of any external object; but perception implies both conception and belief of fomething different from the percipient mind and the act of perception. The want of this diftinction Dr. Reid reprefents as having given occafion to most of the falfe theories of philofophers with regard to the fenfes. They have comprehended both fenfation and percept. n under the fame name, and confidered them as one uncompounded operation. Hence they have called all our notions of material objects ideas of fenfation. Mr. Locke faw that the fenfations excited by what are called fecondary qualities have no refemblance to any thing that pertains to body; and hence concluded, that colour, and fmell, and tafte, and heat, and hardnefs, and the like, do not exist in the object, but are mere ideas in the mind. Dr. Berkeley perceived that the fame obfervation is applicable to primary qualities, and that our fenfations resemble no material obje& whatever. Hence, taking it for granted that the fenfes prefent nothing to the mind but fenfations, he concluded that there is no material world. If the fenfes,' Dr. Reid obferves, furnifhed

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