In oppofition to what I have here obferved on the importance of Dr. Reid's fpeculations concerning our perceptive powers, I am fenfible it may be urged, that they amount merely to a negative discovery; and it is poffible, that fome may even be forward to remark, that it was unneceffary to employ fo much labor and ingenuity as he has done, to overthrow an hypothefis of which a plain account would have been a fufficient refutation.-To fuch perfons, I would beg leave to fuggeft, that, although, in confequence of the jufter views in pneumatology, which now begin to prevail, (chiefly, I believe, in confequence of Dr. Reid's writings,) the ideal fyftem may appear to many readers unphilofophical and puerile; yet the cafe was very different when this author entered upon his inquiries: and I may even venture to add, that few positive discoveries, in the whole history of science, can be mentioned, which found a jufter claim to literary reputation, than to have detected, fo clearly and unanswerably, the fallacy of an hypothefis, which has defcended to us from the earliest ages of philofophy: and which, in modern times, has not only ferved to Berkeley and Hume as the bafis of their fceptical fyftems, but was adopted as an indisputable truth by Locke, by Clarke, and by Newton.

SECTION IV.

Of the Origin of our Knowledge.

THE philofophers who endeavored to explain the operations of the human mind by the theory of ideas, and who took for granted, that in every exertion of thought there exifts in the mind fome object diftinct from the thinking fubftance were naturally led to inquire whence thefe ideas derive their origin; in

particular, whether they are conveyed to the mind from without by means of the fenfes, or from part of its original furniture?

With respect to this question, the opinions of the ancients were various; but as the influence of these opinions on the prevailing fystems of the prefent age is not very confiderable, it is not neceflary, for any of the purposes I have in view in this work, to confider them particularly. The moderns, too, have been much divided on the fubject; fome holding with Des Cartes, that the mind is furnished with certain innate ideas; others, with Mr. Locke, that all our ideas may be traced from fenfation and reflection; and many, (especially among the later metaphyficians in France,) that they may be all traced from fenfation alone.

Of these theories, that of Mr. Locke deferves more particularly our attention; as it has ferved as the bafis of moft of the metaphysical systems which have appeared fince his time; and as the difference between it and the theory which derives all our ideas froin fenfation alone, is rather apparent than real.

In order to convey a juft notion of Mr. Locke's doctrine concerning the origin of our ideas, it is neceffary to remark, that he refers to sensation, all the ideas which we are supposed to receive by the external fenfes; our ideas, for example, of colours, of founds, of hardnefs, of extenfion, of motion; and, in short, of all the qualities and modes of matter; to reflection, the ideas of our own mental operations which we derive from confcioufnefs; our ideas, for example, of memory, of imagination, of volition, of pleasure, and of pain. Thefe two fources, according to him, furnish us with all our fimple ideas, and the only power which the mind poffeffes over them, is to perform certain operations, in the way of compofition, abstraction, generalisation, &c. on the materials which it thus collects in the course of its experi

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ence. The laudable defire of Mr. Locke, to introduce precifion and perfpicuity into metaphyfical fpeculations, and his anxiety to guard the mind against error in general, naturally prepoffeffed him in favor of a doctrine, which, when compared with thofe of his predeceffors, was intelligible and fimple; and which, by fuggefting a method, apparently eafy and palpable, of analyfing our knowledge into its elementary principles, feemed to furnish an antidote against those prejudices which had been favoured by the hypothefis of innate ideas. It is now a confidérable time fince this fundamental principle of Mr. Locke's fyftem began to lofe its authority in England; and the fceptical conclufions, which it had been employed to fupport by fome later writers, furnished its opponents with very plaufible arguments againft it. The late learned Mr. Harris, in particular, frequently mentions this doctrine of Mr. Locke, and always in terms of high indignation. "Mark," (fays he, in one paffage,)" the order of things, according "to the account of our later metaphyficians. Firft, " comes that huge body, the fenfible world. Then "this, and its attributes, beget fenfible ideas. Then, "out of fenfible ideas, by a kind of lopping and pru"ning, are made ideas intelligible, whether fpecific "or general. Thus, fhould they admit that mind "was coeval with body; yet, till body gave it ideas, "and awakened its dormant powers, it could at best "have been nothing more than a fort of dead capa"city; for innate ideas it could not poffibly have

"" any. And, in another paffage : "For my own 66 part, when I read the detail about fenfation and re"flection, and am taught the process at large how my ideas are all generated, I feem to view the hu"man foul, in the light of a crucible, where truths "are produced by a kind of logical chemistry."

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If Dr. Reid's reafonings on the fubject of ideas be admitted, all these fpeculations with refpect to their

origin fall to the ground; and the question to which they relate, is reduced merely to a question of fact ; concerning the occafions on which the mind is firft led to form thofe fimple notions into which our thoughts may be analyfed, and which may be confidered as the principles or elements of human knowledge. With refpect to many of thefe notions, this inquiry involves no difficulty. No one, for example, can be at a lofs to ascertain the occafions on which the notions of colours and founds are first formed by the mind: for these notions are confined to individuals who are poffeffed of particular fenfes, and cannot, by any combination of words, be conveyed to those who never enjoyed the use of them. The history of our notions of extenfion and figure, (which may be fuggefted to the mind by the exercife either of fight or of touch,) is not altogether fo obvious; and accordingly, it has been the fubject of various controverfies. To trace the origin of these, and of our other fimple notions with respect to the qualities of matter; or, in other words, to describe the occafions on which, by the laws of our nature, they are fuggefted to the mind, is one of the leading objects of Dr. Reid's inquiry, in his analyfis of our external fenfes; in which he carefully avoids every hypothefis with respect to the inexplicable phenomena of perception and of thought, and confines himself fcrupulously to a literal statement of facts.-Similar inquiries to thefe, may be propofed, concerning the occafions on which we form the notions of time, of motion, of number, of caufation, and an infinite variety of others. Thus, it has been observed by different authors, that every perception of change fuggefts to the mind the notion of a cause, without which that change could not have happened. Dr. Reid remarks, that, without the faculty of memory, our perceptive powers could never have led us to form the idea of motion. I fhall afterwards fhew, in the sequel of this.

work, that without the fame faculty of memory, we never could have formed the notion of time; and that without the faculty of abstraction, we could not have formed the notion of number.-Such inquiries, with refpect to the origin of our knowledge, are curious and important; and if conducted with judgment, they may lead to the most certain conclufions; as they aim at nothing more than to ascertain facts, which, although not obvious to fuperficial obfervers, may yet be discovered by patient investigation.

From the remarks which have been just made on our notions of time, of motion, and of number, it is evident, that the inquiry concerning the origin of human knowledge cannot poffibly be difcuffed at the commencement of fuch a work as this; but that it must be resumed in different parts of it, as those faculties of the mind come under our view, with which the formation of our different fimple notions is connected.

With respect to the general queftion, Whether all our knowledge may be ultimately traced trom our fenfations? I fhall only observe at present, that the opinion we form concerning it, is of much less confequence than is commonly fuppofed. That the mind cannot, without the groffeft abfurdity, be confidered in the light of a receptacle which is gradually furnished from without, by materials introduced by the channel of the fenfes ; nor in that of a tubula rafa, upon which copies or resemblances of things external are imprinted; I have already fhewn at fufficient length. Although, therefore, we should acquiefce in the conclufion, that, without our organs of fenfe, the mind must have remained destitute of knowledge, this conceffion could have no tendency whatever to favour the principles of materialifm ; as it implies nothing more than that the impreffions made on our fenfes by external objects, furnish the occafions on which the mind, by the laws of its con