by merely perceiving it, I am unable for my own part to comprehend. We are certainly not conscious of such an operation, neither can we observe any external effects attributable to it. To act upon objects is to produce some change in them, and since, by looking on a tree or other visible entity, I certainly produce no change in it, the doctrine in that sense is obviously false. The simplest action of this kind conceivable is spreading colour over objects according to the theory of D'Alembert the value of which has been already exhibited. Let us suppose, therefore, the meaning to be (and this is the only other meaning I can imagine), that the mind operates upon the impression received from the object so as to modify it. If this were the fact, we should of course be conscious, first, of the original impression, and, then, of the act of modifying it. But of this process we are not conscious, nor is it what the supporters of the doctrine can consistently mean; they must intend it to be understood that the impression is, in some way or other, modified in transitu before we become conscious of it or receive it. But, an impression not received (i.e. an impression not impressed) is a contradiction. A physical impression on the organs of sense, or, in other words, a motion communicated to them, may be conceived to be modified on its passage to the brain (if for argument's sake such an expression may be used), by the quality or condition of the nerve; but a mental impression, if modified at all,

must be operated upon after having been produced, as it obviously cannot be modified before it exists. Of such a mental operation we are, I repeat, utterly unconscious.

All these various but equivalent propositions, that the mind attributes their qualities to objects, that it determines the forms or appearances of ob. jects, that it acts upon them, are self-inconsistent; and they are, moreover, assertions of mental events which never occur, of which we have no internal consciousness, which we cannot externally observe, and which are in truth purely imaginary.

They appear to me to have arisen from an oversight or non-appreciation of the simple truth I have before urged, that perceiving external objects is a primary fact of consciousness not susceptible of analysis or explanation, and beyond which it is impossible to go.

You may analyse a compound visible object into its separate parts and attributes,-into its form, its colour, its motion, and so on; but this is an analysis of the thing perceived, not of the act of perception: or you may trace every step of the physical processes of which perception is the result; but this, as I have before remarked, does not in the slightest degree affect the simple and direct character of the act of perception itself.

Perceiving must be considered as a primary state of consciousness in the same way as pain or hunger or fear or joy, the causes of which you may

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ascertain, but the nature of which no knowledge can alter and no explanation elucidate.

Kant thought he had made a great discovery in the method of treating these subjects when he proposed, instead of tracing the effects of objects on the mind, to reverse the process, by tracing the operation of the mind on objects - an operation which never happens to take place comparing his procedure to that of Copernicus when putting aside the hypothesis that the whole heavens revolve round the motionless earth, that celebrated astronomer set himself to try what results would be obtained by supposing the heavens to be stationary and the earth to revolve on its axis.

The German metaphysician, nevertheless, flattered himself with a comparison which he was not entitled to draw.

The single point of analogy between the two cases-certainly not a very extraordinary one-is, that in both there was a change, or an alleged change, in method; and this single point is nothing compared with the concomitant discrepancy in every respect besides. Copernicus abandoned a cumbrous, complicated, and false hypothesis for a simple and true theory, beautifully consistent with all known phenomena; while Kant dismissed a simple and true mode of viewing his subject for an arbitrary supposition, not only without any foundation in facts, but absolutely opposed to them.

LETTER XXI.

IDEAS.

Ir scarcely needs stating, except by way of introduction to what follows, that as there are no independent entities called ideas or images in perception, so there are none in conception.

In the act of conceiving or recollecting an object in its absence, or when it no longer exists, there is obviously nothing but the concipient being affected in a particular way; there is by the supposition no external object before him, and there is no independent image, or form, or phantasm, present to his consciousness. It is simply the man mentally acting or mentally affected.

Thus the acts called respectively perception and conception agree in the negative circumstance, that in neither of them is there any independent entity called an idea or representation; but at the same time they differ in this, that there is in conception, or rather conception itself is, a state of mind corresponding to the term idea or representation, while in perception there is nothing at all to which the term idea or representation can be applied.

The false hypothesis, however, of there being

ideas in perception may have sprung out of the undeniable fact that there are ideas in conception.

As when we turn away from looking at a tree, we are conscious of an idea or image of it remaining, although the tree is no longer in sight, it may have easily occurred to any one that, since the idea of the tree must have been generated while the object was present, the said idea must have then existed in the mind; hence, it may be argued, it is by means of ideas that external objects are perceived, or, what amounts to the same thing, it is the ideas which are perceived and not the objects.

Such a train of loose reasoning would be most likely to occur to those who maintained that the ideas we have, when thinking of external objects, are entities substantially distinct from the mind. On that hypothesis the reflex deduction I have supposed would have much plausibility. Nothing would seem more reasonable than that such independent existences, if they had place in conception, should have previously had place in perception.

But, putting aside separate entities, and taking only the admitted fact that we have ideas of objects in their absence, although such ideas are purely mental modifications, a similar train of thought might be suggested; a reflex transfer of ideas, so to speak, might be made from conception to perception, and what is true of the former ascribed to the latter.