fcended 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 indifputable truth by Locke, by Clarke, and by Newton.

THE

SECTION IV.

Of the Origin of our Knowledge.

HE philofophers who endeavoured 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 diftin&t 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 form part of its original furniture?

With refpect to this question, the opinions of the ancients were various; but as the influence of these opinions on the prevailing fyftems of the prefent age is not very confiderable, it is not neceffary, 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 subject; some 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 metaphysicians in France,) that they may be all traced from fenfation alone.

of

Of these theories, that of Mr. Locke deferves more particularly our attention; as it has ferved as the bafis 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 fuppofed to receive by the external fenses; our ideas, for example, of colours, of founds, of hardness, of extenfion, of motion; and, in fhort, of all the qualities and modes of matter; to reflection, the ideas of our own mental operations which we derive from conscioufnefs; our ideas, for example, of memory, of imagination, of volition, of pleasure, and of pain. These two fources, according to him, furnifh 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 courfe of its experience. The laudable defire of Mr. Locke, to introduce precifion and perfpicuity into metaphysical 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 fuggesting a method, apparently easy and palpable, of analysing 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 con

a confiderable time fince this fundamental principle of Mr. Locke's fyftem began to lose its authority in England; and the fceptical conclufions, which it had been employed to fupport by fome later writers, furnished its opponents with very plausible 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," (says 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 fpecific or general. Thus, "fhould they admit that mind was coeval with body;

yet, till 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 process 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 reasonings on the subject 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 queftion of fact; concerning the occafions on which the mind is first 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 ascertain the occafions on which. the notions of colours and founds are firft 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 fuggested to the mind by the exercise either of fight or of touch,) is not altogether so 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 analysis of our external fenfes; in which he carefully avoids every hypothesis with refpect 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 causation, and an infinite variety of others. Thus, it has been obferved by different authors, that every perception of change fuggefts to the mind the notion of a caufe, without which that change could not have happened. Dr. Reid remarks, that, without the faculty of me mory, our perceptive powers could never have led us to form the idea of motion. I fhall afterwards fhew,

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 abftraction, 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 afcertain 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 hu man knowledge cannot poffibly be difcuffed at the commencement of fuch a work as this; but that it must be refumed 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 refpect to the general queftion, Whether all our knowledge may be ultimately traced from our fenfations? I fhall only obferve at prefent, that the opinion we form concerning it, is of much lefs confequence than is commonly fuppofed. That the mind cannot, without the groffcft abfurdity, be confidered in the light of a receptacle which is gradually furnished from without, by materials introduced by the channel of the fenses; 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