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Of certain natural Prejudices, which seem to have given rise

to the common Theories of Perception.


philosophers, that there is no instance in which we are able to perceive a necessary connexion between two successive 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, ihough 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 difcover them.

I shall endeavour to lhew, in another part of this work, that the doctrine I have now stated does not lead to these sceptical conclusions, concerning the existence of a First Cause, which an author of great ingenuity has attempted to deduce from it. At

present, it is sufficient for my purpose to remark, that the word cause is used, both by philosophers and the

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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 expresses something which is supposed to be necessarily connected with the change ; and without which it could not have happened. This may 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 established course of nature.—The causes which are the objects of our in. vestigation in natural philosophy, may, for the sake of distinction, be called physical causes.

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 speculations, is told, for the first time, that the science of physics gives us no information concerning the efficient causes of the phenomena about which it is employed, he feels some 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 virtues, which fit them to produce particular effects. That we have no reason to believe this to be the case, has been shewn in a very particular manner by Mr.


Hume, and by other writers ; and must, indeed, appear evident to every person, 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 refer. ence 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 existence of a sentient being. Hence, I apprehend, it is, that when we see two events constantly conjoined, we are led to associate the idea of causation, or efficiency, with the former, and to refer to it that power or energy by which the change was produced ; in confequence of which association, we come to consider philosophy as the knowledge of efficient causes; and lose fight of the operation of mind, in producing there, phenomena of nature.-It is by an association fome. what similar, that we connect our sensations of colour, with the primary qualities of body. A moment's re. flection must satisfy any one, that the sensation of co. lour can only reside in a mind ; and yet our natural bias is surely to connect colour with extension and

* See, in particular, Dr. Reid's Essays on the Intellectual Powers of Man. 4


figure, and to conceive white, blue, and yellow, as

something spread over the surfaces of bodies. In the į fame way, we are led to associate with inanimate mat

ter, the ideas of power, force, energy, and caufation ; which are all attributes of mind, and can exist in a mind only.

The bias of our nature is strengthened by another association. Our language, with respect 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 shall follow. In like manner, we see some events, which occasionally follow one another, and which are occasionally dif. joined: we fee 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 ow. ing merely to accidental position ; the others to objects which are tied together by a material vinculum. Hence we transfer to such events, the same 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 we know nothing of physical events, but the laws which regulate their succellion, must, I think, appear

See Note [D].

very obvious to every person who takes the trouble to reflect on the subject; and yet it is certain, that it has milled 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 rise, in natural philosophy, will illustrate clearly the origin of the common theories of perception; and will, at the same time, satisfy the reader, with respect to the train of thought which suggested the foregoing ob. servations.

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.

" What“ ever objects,” says Mr. Hume, “ are considered as “ causes or effects, are contiguous; and nothing can

operate in a time or place, which is ever so little " removed from those of its existence." “ therefore (he adds) consider the relation of conti. “guity as essential to that of causation.”—But although this maxim should be admited, with respect 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 they are the constant forerunners and signs of certain natural events. It may, indeed, be improper, according to this doctrine, to retain the expressions, cause and effect, in na. fural philosophy; but, as long as the present language upon the subject continues in use, the propriety of its

16 We may

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