Of these theories, that of Mr. Locke deserves more particularly our attention; as it has served as the basis of most of the metaphysical systems which have appeared fince his time; and as the difference between it and the theory which derives all our ideas from 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 fenfation, all the ideas which we are supposed to receive by the external senses; our ideas, for example, of colours, of founds, of hardness, of extension, 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 consciousness; our ideas, for example, of memory, of imagination, of volition, of pleasure, and of pain. These two sources, 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, generalifation, &c. on the materials which it thus collects in the courfe of its experience. The laudable defire of Mr. Locke, to introduce precifion and perfpicuity into metaphyfical speculations, and his anxiety to guard the mind against error in general, naturally prepoffeffed him in favour of a doctrine, which, when compared with thofe of his predeceffors, was intelligible and fimple; and which, by fuggefting a method, apparently easy and palpable, of analyfing our knowledge into its elementary principles, seemed to furnish an antidote against those prejudices which had been favoured by the hypothesis of innate ideas. It is now

a confiderable time fince this fundamental principle of Mr. Locke's fyftem began to lofe its authority in England; and the sceptical conclufions, which it had been employed to fupport by fome later writers, furnished its opponents with very plaufible arguments against 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. First, comes that huge body, the fenfible world. Then this, and its attri"butes, beget fenfible ideas. Then, out of fenfible "ideas, by a kind of lopping and pruning, are made "ideas intelligible, whether specific or general. Thus, "should they admit that mind was coëval with body;

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yet, till the body gave it ideas, and awakened its dor"mant powers, it could at beft have been nothing "more than a fort of dead capacity; for innate ideas "it could not poffibly have any.” And, in another paffage: "For my own part, when I read "the detail about fenfation and reflexion, and am "taught the procefs at large how my ideas are all ge"nerated, I feem to view the human foul, in the "light of a crucible, where truths are produced by a "kind of logical chemistry."

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 queftion to which they relate, is reduced merely to a queftion 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 con

fidered

fidered as the principles or elements of human knowledge. With respect to many of these notions, this inquiry involves no difficulty. No one, for example, can be at a lofs to afcertain 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 hiftory of our notions of extenfion and figure,. (which may be suggested to the mind by the exercise either of fight or of touch,) is not altogether fo obvious; and accordingly, it has been the subject 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 defcribe 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 analysis of our external fenfes; in which he carefully avoids every hypothesis 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 fuggests to the mind the notion of a caufe, 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,

H

in the fequel 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 abstrac tion, we could not have formed the notion of number. -Such inquiries, with respect to the origin of our knowledge, are curious and important; and if conducted with judgment, they may lead to the most certain conclusions; as they aim at nothing more than to ascertain facts, which, although not obvious to fuperficial observers, 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 hu man knowledge cannot poffibly be difcuffed at the commencement of such 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 question, Whether all our knowledge may be ultimately traced from our fenfations? I fhall only observe at prefent, that the opinion we form concerning it, is of much lefs confe quence 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 tabula rafa, upon which copies or resemblances of things external are imprinted; I have already fhewn at fufficient length. Although, therefore, we fhould acquiefce in the con

clufion,

clufion, 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 materialism; as it implies nothing more than that the impreffions made on our fenfes by ex. ternal objects, furnifh the occafions on which the mind, by the laws of its constitution, is led to per ceive the qualities of the material world, and to exert all the different modifications of thought of which it is capable.

From the very flight view of the fubject, however, which has been already given, it is fufficiently evident, that this doctrine, which refers the origin of all our knowledge to the occafions furnished by fenfe, must be received with many limitations. That thofe ideas, which Mr. Locke calls ideas of reflexion, (or, in other words, the notions which we form of the subjects of our own consciousness,) are not suggested to the mind immediately by the fenfations arifing from the use of our organs of perception, is granted on all hands; and, therefore, the amount of the doctrine now mentioned, is nothing more than this; that the first occafions on which our various intellectual faculties are exercised, are furnished by the impreffions made on our organs of sense; and confequently, that, without these impreffions, it would have been impoffible for us to arrive at the knowledge of our faculties. Agreeably to this explanation of the doctrine, it may un. doubtedly be faid with plaufibility, (and, I am in. clined to believe, with truth,) that the occafions on which all our notions are formed, are furnished either immediately or ultimately by sense; but, if I am not