(however infinitesimal the portion) of doubt, and, consequently, tends to the confusion of intellectual phenomena, which accuracy of thought requires to be carefully distinguished. It unsettles and renders indefinite the acceptation of both knowing and. believing.

I must crave your patience while I proceed to mention another radical fallacy in the ideal theory, whatever may be the form in which it is presented. There is in it a latent self-contradiction which I think you will readily discover when I point it out. Although my argument lies more directly against Berkeley's form of the theory, it will apply, mutatis mutandis, to any other.

Mark what is comprehended in the assertion here in question, that we perceive ideas in the mind, and do not perceive independent external objects. By it two classes of entities are plainly discriminated: ideas in the mind are placed in contradistinction to material things out of the mind.

Well, observe the consequences: in order to place two things in contradistinction to each other, you must of course know both. When you assert that objects are only ideas in the mind, not things out of the mind, you must, in order to speak rationally and consistently, know what things out of the mind are.

But, as the theoretic idealist denies altogether this knowledge of independent material things out of the mind, he is precluded from predicating what

they are or what they are not; and, consequently, when he speaks of them at all, and especially in contradistinction to ideas in the mind, it must be without any meaning except what is derived from the palpable self-contradiction of assuming the knowledge he denies. He cannot form any proposition about them without presupposing their having been perceived as external.

When he tells us that it is impossible there should be any such thing as an outward object, how or where did he obtain the meaning of the last term of his own assertion?

If, indeed, these ideas were truly the sole things that we perceive, neither Berkeley nor any other philosopher could ever have dreamed of asserting that we know nothing else, any more than the silliest babbler in science would dream of informing his neighbours that gold is only gold, and not an unknown substance x.

The very position, in a word, that we perceive nothing but ideas in the mind could not have been thought of unless we had perceived something different from them-something out of the mind.

A Berkeleian is reduced, in truth, to this dilemma: if he knows what external things are, it can be only by perceiving them as external,-which contradicts his theory. If, on the other hand, he does not know what they are, he is incapable of using the expression external with any meaning, and could,

in fact, never have invented or thought of employing it.

The same result is obtained from Berkeley's doctrine of the correspondence of perception and conception, a point of view which merely exhibits the contradiction in a slightly varied form. He repeatedly insists that we can conceive nothing except as we have perceived it. "My conceiving power,” he says, "does not extend beyond real existence or perception." But he also teaches that we cannot perceive objects as external; we consequently cannot conceive them as external. When, therefore, he speaks of external objects, he speaks of things of which, by his own doctrine, he can form no conception-in other words, he falls into unmeaning propositions.

Again, his assertions afford this curious result.

When he affirms it to be impossible to conceive anything otherwise than as we have perceived it, he means, according to his own interpretation, that we can conceive only those ideas which the Author of Nature had previously imprinted on the senses. Well, then, the Deity either imprints the tree before me on my senses, as external, or he does not if he does, then the tree is external, or he imprints what is false; if he does not imprint it as external, how came I by such an impression or idea at all?

LETTER XVIII.

THEORIES OF PERCEPTION CONTINUED.

D'ALEMBERT, AND STEWART.

THE course of these discussions has brought me to a point that is favourable for considering some parts of the subject of perception which have seldom been perspicuously treated.

A common misapprehension about perception appears to me to arise from not clearly and steadily distinguishing the material operations concerned and the conscious state which is the result of them.

The whole process may be described in general terms as follows:

Certain qualities in the object external to our bodily frame, whether operating or not through an inorganic medium, interposed between the object and the organs of sense, occasion certain conditions in the matter composing or pervading our nerves and brain. These conditions in the nerves and brain are followed or accompanied by certain states of consciousness, which states of consciousness we designate by the phrase, the perception of external objects.

Now it is important to remark two facts in

relation to such cases of action on our nervous system:

1. When we perceive an object, we have not any consciousness of the conditions of the nerves and brain concerned in the resulting act of perception, nor of the motions of any inorganic medium between the object and our organ: we are conscious of perceiving the external object, and nothing else. In seeing we are not conscious of the retina, nor of the rays of light impinging upon it, nor of the picture there delineated. In hearing we are not conscious of the drum of the ear, nor of the pulses of the air by which it is struck, nor, in either case, of any communication between those parts and the brain.

2. As we are unconscious of the physical process, so what we are conscious of perceiving is not at all affected by our being able or unable to trace that process of which perception is the result. In other words, our perception of external objects is not alterable by any insight or want of insight into its physical causes. What is designated by the words "seeing an object," is the same mental state in the child, the savage, and the philosopher, and as a simple modification of consciousness neither wants nor admits of any analysis or explanation. Although the physical events leading to it may be minutely investigated, it cannot itself be resolved into any other mental state or states.

You may trace the course of light from the