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senses, obviously unintelligible and self-contradictory. As to the objects of sight,” says 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 absolute “ 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 hardness or softness, an image “ of sound, or smell, or taste. The word image, when “ appied to these objects of sense, has absolutely no “ meaning.”—This palpable imperfection in the ideal theory, has plainly taken rise from the natural or. der in which the phenomena of perception present themselves to the curiosity.

The mistakes, which have been so long current in the world, about this part of the human confitution, will, i hope, justify me for prosecuting the subject a little farther; in particular, for illustrating, at lome 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 respect to the object, and the limits, of philosophical inquiry ; to which I shall frequently have occasion to refer, in the course of the following disquisitions.


Of certain natural prejudices, which seem to have given

rise to the common Theories of Perception. IT seems now to be pretty generally agreed a.. mong philosophers, that there is no instance in which we are able to perceive a neceffary connexion between two fucceflive 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 constantly conjoined, so that the one invariably follows the other : but it is possible, for any thing we know to the contrary, that this connexion, though a constant one, as far as our observation has reached, may not be a necessary connexion ; nay, it is possible, that there may be no necessary connexions among any of the phenomena we fee : and if there are any such connexions existing, we may rest assured that we shall never be able to discover them.*

I shall endeavor to shew, in another part of this work, that the doctrine I have now stated does not lead to those sceptical conclusions, concerning the existence of a First Cause, which an author of great in. genuity has attempted to deduce from it. At pres. ent, it is sufficient for my purpose to remark, that the word cause is used, both by philosophers and the vulgar, in two senses, which are widely different.When it is said, that every change in nature indicates the operation of a cause, the word cause expreffes fomething which is fupposed to be necessarily connected with the change ; and without which it could not have happened. This inay be called the metaphysical meaning of the word ; and such causes may be called metaphysical or efficient causes. In natural philosophy, however, when we speak of one thing being the cause of another, all that we mean is, that the two are constantly conjoined ; so that, when we see the one, we may expect the other. These conjunctions we learn from experience alone ; and without an acquaintance with them, we could not accommodate our conduct to the eftablified course of nature. The causes which are the objects of our investigation in natural philosophy, may, for the sake of distinction, be called physical causes.

* See note [C]

I am very ready to acknowledge, that this doctrine, concerning the object of natural philosophy, is not altogether agreeable to popular prejudices. When a man, unaccustomed to metaphysical specu. lations, is told, for the first time, that the science of physics gives us no information concerning the effi. cient causes of the phenomena about which it is employed, he feels fome degree of surprise and mortification. The natural bias of the mind, is surely to conceive physical events as somehow linked together ; and material substances, as possessed of certain powers and vi

and virtues, which fit them to produce particular effects. That we have no reason to believe this to be the case, has been fewn in a very satisfactory manner by Mr. Hume, and by other writers; and must, indeed, appear evident to every perfon, on a moment's reflection. It is a curious question, what gives rise to the prejudice ?

In stating the argument for the existence of the Deity, several modern philosophers 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 result of reasoning, but necessarily accompanies the perception, so as to render it impoffible for us to see the change, without feeling a conviction of the operation of some cause by which it was produced ; much in the same manner in which we find it to be impossible to conceive a sensation, without being impressed with a belief of the exiftence of a fentient being. Hence, I apprehend, it is, that when we see two events constantly conjoined, we are led to associate 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 consequence of which association, we come to

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

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confider philosophy as the knowledge of efficient causes ; and lose fight of the operation of mind, in producing the phenomena of nature.--It is by an afsociation somewhat similar, that we connect our sensations of color, with the primary qualities of body. A moment's reflection must satisfy any one, that the sensation of color can only reside in a mind ; and yet our natural bias is surely to connect color with extension and figure, and to conceive white, blue, and yellow, as something spread over the bodies. In the same way, we are led to associate with inanimate matter, the ideas of power, force, cnergy, and causation ; which are all attributes of mind, and can exist in a mind only.

This bias of our nature is strengthened by another affociation. Our language, with refpect to cause and effect, is borrowed by analogy from material objects. Some of these we see scattered about us, without any connexion between them ; so that one of them may be removed from its place, without disturbing the rest. We can, however, by means of some material vinculum, connect two or more objects together; so that whenever the one is moved, the others thall follow. In like manner, we see some events, which occasionally follow one another, and which are occasionally disjoined : we see others, where the succession is constant and invariable. The former we conceive to be analogous to objects which are loose, and unconnected with each other, and whose contiguity in place, is owing merely to accidental position ; the others to objects, which are tied to. gether by a material vinculum. Hence we transfer to such events, the fame language which we apply to connected objects. We speak of a connexion between two events and of a chain of causes 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 succession, must, I think, appear very obvious to every person who takes the trouble to reflect on the subject ; and yet it is certain, that it has misled the greater part of philosophers; and has had a surprising influence on the systems, which they have formed in very different departments of science.

A few remarks, on some of the mistaken conclu. fions, to which the vulgar notions concerning the connexions among physical events have given rile, in natural philosophy, will illustrate clearly the origin of the common theories of perception ; and will, at the same time, fatisfy the reader, with respect to the train of thought which suggested the foregoing observations.

The maxim, that nothing can act but where it is, and when it is, has always been admitted, with respect to metaphysical or efficient causes. " Whatever ob" "jects,” says Mr. Hume,“ are considered as causes “ or effects, are contiguous ; and nothing can ope

rate in a time or place, which is ever so sittle re. moved from those of its existence.” “therefore (he adds) consider the relation of conti“ guity as effential to that of caufation."-But although this maxim should be admitted, with refpect to causes which are efficient, and which, as such, are necessarily connected with their effects, there is surely no good reason for extending it to physical causes, of which we know nothing, but that are the constant forerunners and ligns of certain natural events. It mnay, indeed, be improper, according to this doctrine, to retain the expressions, cause and effect, in natural philofophy ; but, as long as the present language upon the subject continues in use, the propriety of its application, in any particular instance, does not depend on the contiguity of the two events in place or time, but solely on this question, whether the one event be the constant and invaria.

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