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In opposition to what I have here observed on the importance of Dr. Reid's fpeculations concerning our perceptive powers, I am sensible it may be urged, that they amount merely to a negative discovery; and it is poflible, that fome may even be forward to remark, that it was unnecessary to employ so much Jabor and ingenuity as he has done, to overthrow an hypothesis of which a plain account would have been a sufficient refutation.-To fuch perfons, I would beg leave to suggest, that, although, in consequence of the juster views in pneumatology, which now begin to prevail, (chiefly, I believe, in consequence of Dr. Reid's writings,) the ideal fyftem may appear to many readers unphilofophical and puerile ; yet the case 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, so clearly and unanswerably, the fallacy of an hypothesis, which has descended to us from the earliest ages of philosophy : and which, in modern times, has not only served to Berkeley and Hume as the basis of their sceptical systems, but was adopted as an indisputable truth by Locke, by Clarke, and by Newton.
Of the Origin of our Knowledge.
THE philosophers 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 exilts in the mind some object distinct from the thinking substance were naturally led to inquire whence these ideas derive their origin; in particular, whether they are conveyed to the mind from without by means of the senses, 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 systems of the present age is not very considerable, it is not necessary, 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 ; 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 sensation and reflection ; and many, (especially among the later metaphysicians in France,) that they may be all traced from fenfam tion alone.
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 froin fenfation alone, is rather apparent than real.
In order to convey a just notion of Mr. Locke's doctrine concerning the origin of our ideas, it is necessary to remark, that he refers to sensation, 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 fources, according to him, furnish us with all our fimple ideas, and the only power which the mind poffefses over them, is to perform certain operations, in the way of composition, abstraction, generalisation, &c. on the materials which it thus collects in the course of its experi
ence, The laudable desire of Mr. Locke, to introduce precision and perspicuity into metaphysical speculations, and his anxiety to guard the mind against error in general, naturally prepofseffed him in favor of a doctrine, which, when compared with those of his predecessors, was intelligible and simple ; and which, by suggesting a method, apparently easy and palpable, of analysing 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 since this fundamental principle of Mr. Locke'ssystem began to lose its authority in England; and the sceptical conclusions, which it had been employed to support by some later writers, furnished its opponents with very plausible 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,” (says he, in one paffage,)" the order of things, according “ to the account of our later metaphysicians. First, " comes that huge body, the sensible world. Then “ this, and its attributes, beget sensible ideas. Then, “ out of sensible ideas, by a kind of lopping and pru“ning, are made ideas intelligible, whether specific
or general. Thus, should they admit that mind “ was coëval with body; yet, till body gave it ideas, 6 and awakened its dormant powers, it could at best “ have been nothing more than a sort of dead capa
city ; for innate ideas it could not possibly have any. And, in another passage : “For my own
part, when I read the detail about sensation and re“ flection, and am taught the process at large how “ my ideas are all generated, I seem to view the hu
man soul, 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 speculations with respect to their
origin fall to the ground; and the question to which they relate, is reduced merely to a question of fact; concerning the occasions on which the mind is first led to form those fimple notions into which our thoughts may be analysed, and which may be conlidered 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 loss to ascertain the occasions on which the notions of colours and sounds are first formed by the mind : for these notions are confined to individuals who are poffeffed of particular senses, and cannot, by any combination of words, be conveyed to those who never enjoyed the use of them. The history of our notions of extension and figure, (which may be suggested to the mind by the.exercise either of sight or of touch,) is not altogether fo obvious ; and accordingly, it has been the subject of various controversies. To trace the origin of these, and of our other simple notions with respect to the qualities of matter; or, in other words, to describe the occasions on which, by the laws of our nature, they are suggested to the mind, is one of the leading objects of Dr. Reid's inquiry, in his analysis of our external senses; 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 these, may be proposed, concerning the occasions 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 suggests 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 shall afterwards thew, in the sequel of this. work, that without the same 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 respect to the origin of our knowledge, are curious and important; and if conducted with judg. ment, they may lead to the most certain conclusions ; as they aim at nothing more than to ascertain facts, which, although not obvious to superficial 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 human knowledge cannot poflibly be discussed 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 simple notions is connected.
With respect to the general question, Whether all our knowledge may be ultimately traced trom our sensations ? I shall only observe at present, that the opinion we form concerning it, is of much less consequence than is commonly supposed. That the mind cannot, without the grosseft absurdity, be con. sidered 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 rufa, upon which copies or resemblances of things external are imprinted ; I have already shewn at fufficient length. Although, therefore, we should acquiesce in the conclusion, that, without our organs of sense, the mind must have remained destitute of knowledge, this concession could have no tendency whatever to favour the principles of materialism ; as it implies nothing more than that the impressions made on our senses by external objects, furnish the occasions on which the mind, by the laws of its con