It is true, would we hearken to certain philosophers, they promise to diminish our ignorance; but I am afraid it is at the hazard of running us into contradictions, from which the subject is of itself exempted. These philosophers are the curious reasoners concerning the material or immaterial substances, in which they suppose our perceptions to inhere. In order to put a stop to these endless cavils on both sides, I know no better method, than to ask these philosophers in a few words, What they mean by substance and inhesion? And after they have answered this question, it will then be reasonable, and not till then, to enter seriously into the dispute.
This question we have found impossible to be answered with regard to matter and body: But besides that in the case of the mind, it labours under all the same difficulties, it is burdened with some additional ones, which are peculiar to that subject. As every idea is derived from a precedent impression, had we any idea of the substance of our minds, we must also have an impression of it; which is very difficult, if not impossible, to be conceived. For how can an impression represent a substance, otherwise than by resembling it? And how can an impression resemble a substance, since, according to this philosophy, it is not a substance, and has none of the peculiar qualities or characteristics of a substance?
But leaving the question of what may or may not be, for that other what actually is, I desire those philosophers, who pretend that we have an idea of the substance of our minds, to point out the impression that produces it, and tell distinctly after what manner that impression operates, and from what object it is derived. Is it an impression of sensation or of reflection? Is it pleasant, or painful, or indifferent? Does it attend us at all times, or does it only return at intervals? If at intervals, at what times principally does it return, and by what causes is it produced?
If instead of answering these questions, anyone should evade the difficulty, by saying, that the definition of a substance is something which may exist by itself; and that this definition ought to satisfy us: should this be said, I should observe, that this definition agrees to everything, that can possibly be conceived; and never will serve to distinguish substance from accident, or the soul from its perceptions. For thus I reason. Whatever is clearly conceived may exist; and whatever is clearly conceived, after any manner, may exist after the same manner. This is one principle, which has been already acknowledged. Again, everything, which is different, is distinguishable, and everything which is distinguishable, is separable by the imagination. This is another principle. My conclusion from both is, that since all our perceptions are different from each other, and from everything else in the universe, they are also distinct and separable, and may be considered as separately existent, and may exist separately, and have no need of anything else to support their existence. They are, therefore, substances, as far as this definition explains a substance.
Thus neither by considering the first origin of ideas, nor by means of a definition are we able to arrive at any satisfactory notion of substance; which seems to me a sufficient reason for abandoning utterly that dispute concerning the materiality and immateriality of the soul, and makes me absolutely condemn even the question itself. We have no perfect idea of anything but of a perception. A substance is entirely different from a perception. We have, therefore, no idea of a substance. Inhesion in something is supposed to be requisite to support the existence of our perceptions. Nothing appears requisite to support the existence of a perception. We have, therefore, no idea of inhesion. What possibility then of answering that question, Whether perceptions inhere in a material or immaterial substance, when we do not so much as understand the meaning of the question?
There is one argument commonly employed for the immateriality of the soul, which seems to me remarkable. Whatever is extended consists of parts; and whatever consists of parts is divisible, if not in reality, at least in the imagination. But it is impossible anything divisible can be conjoined to a thought or perception, which is a being altogether inseparable and indivisible. For supposing such a conjunction, would the indivisible thought exist on the left or on the right hand of this extended divisible body? On the surface or in the middle? On the back- or fore-side of it? If it be conjoined with the extension, it must exist somewhere within its dimensions. If it exist within its dimensions, it must either exist in one particular part; and then that particular part is indivisible, and the perception is conjoined only with it, not with the extension: Or if the thought exists in every part, it must also be extended, and separable, and divisible, as well as the body; which is utterly absurd and contradictory. For can anyone conceive a passion of a yard in length, a foot in breadth, and an inch in thickness? Thought, therefore, and extension are qualities wholly incompatible, and never can incorporate together into one subject.
This argument affects not the question concerning the substance of the soul, but only that concerning its local conjunction with matter; and therefore it may not be improper to consider in general what objects are, or are not susceptible of a local conjunction. This is a curious question, and may lead us to some discoveries of considerable moment.
The first notion of space and extension is derived solely from the senses of sight and feeling; nor is there anything, but what
