The very fhort and imperfect review we have now taken, of the common theories of perception, is almost fufficient, without any commentary, to eftablish the truth of the two general obfervations formerly made; for they all evidently proceed on a fuppofition, fuggefted by the phenomena of phyfics, that there muft of neceflity 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 dif tinction 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 fpeculations, 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 should 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 endeavored, as it were, to spiritualize the nature of their medium; while, at the fame time, all their language concerning it, implied fuch a reference to matter, as was neceflary 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 hiftorical review; that, in the order of inquiry, the phenomena of vifion had firft engaged the attention of philofophers; and had fuggefted to them the greater part of their language, with refpect to perception in general; and that in confequence of this circumftance, the common modes of expreffion on the fubject, unphilofophical and fanciful at beft, even when appli. ed to the fenfe of feeing,are,in the cafe of all the other

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

figure in the brain: but how shall we conceive "an image of their colour, where there is abfolute "darkness? And, as to all other objects of fense, 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 abtolutely no "meaning."-This palpable imperfection in the ideal theory, has plainly taken rife from the natural order in which the phenomena of perception present themselves to the curiosity.

The mistakes, which have been fo 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 philofophical 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 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 oth er: but it is poffible, for any thing we know to the contrary, that this connexion, though a conftant one, as far as our observation has reached, may not be a neceffary 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 fhall 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 those sceptical conclufions, concerning the existence 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 expreff. es 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 causes.-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 see 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 causes which are the objects of our investigation in natural philofophy, may, for the fake of diftinction, be called phyfical caufes.

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 science of phyfics gives us no information concerning the efficient causes of the phenomena about which it is employed, he feels fome degree of surprise and mortifi cation. 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 reafon to believe this to be the cafe, has been fhewn in a very fatisfactory manner by Mr. Hume, and by other writ ers; and muft, indeed, appear evident to every perfon, on a moment's reflection. It is a curious quef tion, 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 cause.*This reference is not the refult of reasoning, 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 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 pow. er 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 affociation 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 caufation; 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 fcattered 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 whofe 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 speak of a connexion be tween two events, and of a chain of caufes and effects.* That this language is merely analogical, and that

* See Note [D.]