the truth of the two general obfervations formerly made; for they all evidently proceed on a fuppofition, fuggested by the phenomena of phyfics, that there muft of neceffity exift fome medium of communication between the objects of perception and the percipient mind; and they all indicate a fecret conviction in their authors, of the effential diftinction between mind and matter; which, although not rendered, by reflection, fufficiently precife and fatisfactory, to fhew them the abfurdity of attempting to explain the mode of their communication; had yet fuch a degree of influence on their speculations, as to induce them to exhibit their fuppofed medium under as mysterious and ambiguous a form as poffible, in order that it might remain doubtful, to which of the two predicaments, of body or mind, they meant that it fhould be referred. By refining away the groffer qualities of matter; and by allufions to fome of the most aerial and magical appearances it affumes, they endeavoured, as it were, to fpiritualize the nature of their medium; while, at the fame time, all their language concerning it, implied fuch a reference to matter, as was neceffary for furnishing a plaufible foundation, for applying to it the received maxims of natural philofophy.

Another obfervation, too, which was formerly hinted at, is confirmed by the fame historical review; that, in the order of inquiry, the phenomena of vi fion had firft engaged the attention of philofophers; and had suggested to them the greater part of their language, with refpect to perception in general; and that, in confequence of this circumftance, the com

mon modes of expreffion on the fubject, unphilofophical and fanciful at beft, even when applied to the sense of seeing, are, in the cafe of all the other fenfes, obviously unintelligible and felf-contradictory," As "to objects of fight," fays Dr. Reid, "I understand "what is meant by an image of their figure in the "brain but how fhall we conceive an image of "their colour, where there is abfolute darkness? "And, as to all other objects of fenfe, except figure "and colour, I am unable to conceive what is meant "by an image of them. Let any man fay, what he "means by an image of heat and cold, an image of "hardnefs or foftnefs, an image of found, or fmell, "or tafte. The word image, when applied to these "objects of fenfe, has abfolutely no meaning." This palpable imperfection in the ideal theory, has plainly taken rife from the natural order in which the phenomena of perception prefent themfelves to the curiofity.

The mistakes, which have been fo long current in the world, about this part of the human constitution, will, I hope, juftify me for profecuting the fubject a little farther; in particular, for illuftrating, at fome length, the first of the two general remarks already. referred to. This fpeculation I enter upon the more willingly, that it affords me an opportunity of ftating fome important principles with refpect to the object, and the limits, of philofophical inquiry; to which Į fhall frequently have occafion to refer, in the course of the following difquifitions.

SECTION II.

Of certain natural Prejudices, which seem to have given rise to the common Theories of Perception.

feems now to be pretty generally agreed among philofophers, that there is no inftance in which we are able to perceive a neceffary connexion between two fucceffive events; or to comprehend in what manner the one proceeds from the other, as its cause. From experience, indeed, we learn, that there are many events, which are conftantly conjoined, fo that the one invariably follows the other: but it is poffible, for any thing we know to the contrary, that this connexion, though a conftant one, as far as our obfervation has reached, may not be a neceffary con. nexion; nay, it is poffible, that there may be no neceffary connexions among any of the phenomena we fee and if there are any fuch connexions exifting, we may rest affured that we shall never be able to discover them *.

I fhall endeavour to fhew, in another part of this work, that the doctrine I have now ftated does not lead to thofe fceptical conclufions, concerning the existence of a First Cause, which an author of great ingenuity has attempted to deduce from it.-At prefent, it is fufficient for my purpose to remark, that the word caufe is ufed, both by philofophers and the

vulgar, in two fenfes, which are widely different.When it is faid, that every change in nature indicates the operation of a caufe, the word cause expresses fomething which is fuppofed to be neceffarily connected with the change; and without which it could not have happened. This may be called the metaphyfical meaning of the word; and fuch caufes may be called metaphyfical or efficient caufes.-In natural philofophy, however, when we fpeak of one thing being the cause of another, all that we mean is, that the two are conftantly conjoined; fo that, when we fee the one, we may expect the other. Thefe conjunctions we learn from experience alone; and without an acquaintance with them, we could not accommodate our conduct to the established courfe of nature. The caufes which are the objects of our investigation in natural philofophy, may, for the fake of distinction, be called phyfical caufes.

I am very ready to acknowledge, that this doctrine, concerning the object of natural philofophy, is not altogether agreeable to popular prejudices. When a man, unaccustomed to metaphyfical fpeculations, is told, for the first time, that the fcience of phyfics gives us no information concerning the efficient caufes of the phenomena about which it is employed, he feels fome degree of surprise and mortification. The natural bias of the mind, is furely to conceive phyfical events as fomehow linked together; and material fubftances, as poffeffed of certain powers and virtues, which fit them to produce particular effects. That we have no reason to believe this to be the case, has been fhewn in a very fatisfactory manner by Mr.

Hume,

Hume, and by other writers; and muft, indeed, appear evident to every perfon, on a moment's reflection. It is a curious queftion, what gives rife to the prejudice?

In ftating the argument for the existence of the Deity, feveral modern philofophers have been at pains to illustrate that law of our nature, which leads us to refer every change we perceive in the universe, to the operation of an efficient caufe *.-This reference is not the refult of reafoning, but neceffarily accompanies the perception, fo as to render it impof. fible for us to fee the change, without feeling a conviction of the operation of fome caufe by which it was produced; much in the fame manner in which we find it to be impoffible to conceive a sensation, without being impreffed with a belief of the existence of a fentient being. Hence, I apprehend, it is, that when we see two events conftantly conjoined, we are led to affociate the idea of caufation, or efficiency, with the former, and to refer to it that power or energy by which the change was produced; in confequence of which affociation, we come to confider philofophy as the knowledge of efficient caufes; and lofe fight of the operation of mind, in producing the phenomena of nature. It is by an affociation fomewhat fimilar, that we connect our fenfations of colour, with the primary qualities of body. A moment's reflection must fatisfy any one, that the sensation of colour can only refide in a mind; and yet our natural bias is furely to connect colour with extenfion and

* See, in particular, Dr. Reid's Effays on the Intellectual Powers of Man.