fenfes, obviously unintelligible and felf-contradictory." As to the objects of fight," fays Dr. Reid, "I "understand what is meant by an image of their

66

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 sense, 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 themselves to the curiofity.

The mistakes, which have been so long current in the world, about this part of the human conftitution, 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 philosophical inquiry; to which I fhall frequently have occafion to refer, in the courfe of the following difquifitions.

SECTION II.

Of certain natural prejudices, which feem to have given rife to the common Theories of Perception.

IT feems now to be pretty generally agreed a mong 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 neceflary connexion; 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 reft affured that we shall never be able to discover them.*

I fhall endeavor to fhew, in another part of this work, that the doctrine I have now ftated does not lead to thofe fceptical conclufions, concerning the exiftence of a First Caufe, which an author of great ingenuity has attempted to deduce from it. At pref ent, it is fufficient for my purpose to remark, that the word cause 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 caufe expreffes fomething which is fupposed to be neceffarily connected with the change; and without which it could not have happened. This may be called the métaphyfical meaning of the word; and fuch caufes may be called metaphyfical or efficient caufes.-In natural philofophy, however, when we speak of one thing being the caufe 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 course of nature.-The caufes which are the objects of our investigation in natural philofophy, may, for the fake of diftinction, be called phyfical causes.

* See note [C].

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 causes of the phenomena about which it is employed, he feels fome degree of furprise and mortification. The natural bias of the mind, is furely to conceive physical 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 cafe, has been fhewn in a very fatisfactory manner by Mr. 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 exiftence 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 impoffible for us to fee the change, without feeling a conviction of the operation of some caufe by which it was produced; much in the fame manner in which we find it to be impoffible to conceive a fenfation, without being impreffed with a belief of the exiftence of a fentient being. Hence, I apprehend, it is, that when we fee 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

* See, in particular, Dr. Reid's Essays on the Intellectual Pow ers of Man.

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 af fociation fomewhat fimilar, that we connect our fenfations of color, with the primary qualities of body. A moment's reflection muft fatisfy any one, that the fenfation of color can only refide in a mind; and yet our natural bias is furely to connect color with extenfion and figure, and to conceive white, blue, and yellow, as fomething spread over the bodies. In the fame way, we are led to affociate with inanimate matter, the ideas of power, force, energy, and causation; which are all attributes of mind, and can exist in a mind only.

This bias of our nature is ftrengthened by another affociation. Our language, with refpect to cause and effect, is borrowed by analogy from material objects. Some of these we fee scattered about us, without any connexion between them; fo that one of them may be removed from its place, without disturbing the reft. We can, however, by means of fome material vinculum, connect two or more objects together; fo that whenever the one is moved, the others fhall follow. In like manner, we fee fome events, which occafionally follow one another, and which are occafionally disjoined: we fee others, where the fucceffion is conftant and invariable. The former we conceive to be analogous to objects which are loofe, and unconnected with each other, and whose contiguity in place, is owing merely to accidental pofition; the others to objects, which are tied together by a material vinculum. Hence we transfer to fuch events, the fame language which we apply to connected objects. We fpeak of a connexion between two events, and of a chain of caufes and effects. That this language is merely analogical, and that

* See Note [D.]

we know nothing of physical events, but the laws which regulate their fucceffion, must, I think, appear very obvious to every person who takes the trouble to reflect on the fubject; and yet it is certain, that it has mifled the greater part of philofophers; and has had a furprising influence on the fyftems, which they have formed in very different departments of fcience.

A few remarks, on fome of the miftaken conclufions, to which the vulgar notions concerning the connexions among phyfical events have given rife, in natural philofophy, will illuftrate clearly the origin of the common theories of perception; and will, at the fame time, fatisfy the reader, with respect to the train of thought which fuggefted the foregoing obfervations.

The maxim, that nothing can act but where it is, and when it is, has always been admitted, with respect to metaphyfical or efficient causes. "Whatever ob"jects," fays Mr. Hume," are confidered as caufes "or effects, are contiguous; and nothing can ope"rate in a time or place, which is ever fo little re"moved from those of its existence.' "We may "therefore (he adds) confider the relation of contiguity as effential to that of caufation."-But although this maxim fhould be admitted, with refpect to caufes which are efficient, and which, as fuch, are neceffarily connected with their effects, there is furely no good reafon for extending it to phyfical caufes, of which we know nothing, but that they are the conftant forerunners and signs of certain natural events. It may, indeed, be improper, according to this doctrine, to retain the expreffions, caufe and effect, in natural philofophy; but, as long as the prefent language upon the fubject continues in use, the propriety of its application, in any particular inftance, does not depend on the contiguity of the two events in place or time, but folely on this question, whether the one event be the conftant and invaria