This argument will appear entirely conclusive to every one that comprehends it; but because it may seem abstruse and intricate to the generality of readers, I hope to be excused, if I endeavour to render it more obvious by some variation of the expression. In order to form an idea of solidity, we must conceive two bodies pressing on each other without any penetration; and it is impossible to arrive at this idea, when we confine ourselves to one object, much more without conceiving any. Two non-entities cannot exclude each other from their places; because they never possess any place, nor can be endowed with any quality. Now I ask, what idea do we form of these bodies or objects, to which we suppose solidity to belong? To say, that we conceive them merely as solid, is to run on in infinitum.

To affirm, that we paint them out to ourselves as extended, either resolves all into a false idea, or returns in a circle. Extension must necessarily be considered either as coloured, which is a false idea; I or as solid, which brings us back to the first question. We may make the same observation concerning mobility and figure; and upon the whole must conclude, that after the exclusion of colours, sounds, heat and cold from the rank of external existences, there remains nothing, which can afford us a just and constituent idea of body.

Add to this, that, properly speaking, solidity or impenetrability is nothing, but an impossibility of annihilation, as[8] has been already observed: For which reason it is the more necessary for us to form some distinct idea of that object, whose annihilation we suppose impossible. An impossibility of being annihilated cannot exist, and can never be conceived to exist, by itself: but necessarily requires some object or real existence, to which it may belong. Now the difficulty still remains, how to form an idea of this object or existence, without having recourse to the secondary and sensible qualities.

[8] Part II. Sect. 4.

Nor must we omit on this occasion our accustomed method of examining ideas by considering those impressions, from which they are derived. The impressions, which enter by the sight and hearing, the smell and taste, are affirmed by modern philosophy to be without any resembling objects; and consequently the idea of solidity, which is supposed to be real, can never be derived from any of these senses. There remains, therefore, the feeling as the only sense, that can convey the impression, which is original to the idea of solidity; and indeed we naturally imagine, that we feel the solidity of bodies, and need but touch any object in order to perceive this quality. But this method of thinking is more popular than philosophical; as will appear from the following reflections.

First, It is easy to observe, that though bodies are felt by means of their solidity, yet the feeling is a quite different thing from the solidity; and that they have not the least resemblance to each other. A man, who has the palsey in one hand, has as perfect an idea of impenetrability, when he observes that hand to be supported by the table, as when he feels the same table with the other hand. An object, that presses upon any of our members, meets with resistance; and that resistance, by the motion it gives to the nerves and animal spirits, conveys a certain sensation to the mind; but it does not follow, that the sensation, motion, and resistance are any ways resembling.

Secondly, The impressions of touch are simple impressions, except when considered with regard to their extension; which makes nothing to the present purpose: And from this simplicity I infer, that they neither represent solidity, nor any real object. For let us put two cases, viz. that of a man, who presses a stone, or any solid body, with his hand, and that of two stones, which press each other; it will readily be allowed, that these two cases are not in every respect alike, but that in the former there is conjoined with the solidity, a feeling or sensation, of which there is no appearance in the latter. In order, therefore, to make these two cases alike, it is necessary to remove some part of the impression, which the man feels by his hand, or organ of sensation; and that being impossible in a simple impression, obliges us to remove the whole, and proves that this whole impression has no archetype or model in external objects. To which we may add, that solidity necessarily supposes two bodies, along with contiguity and impulse; which being a compound object, can never be represented by a simple impression.

Not to mention, that though solidity continues always invariably the same, the impressions of touch change every moment upon us; which is a clear proof that the latter are not representations of the former.

Thus there is a direct and total opposition betwixt our reason and our senses; or more properly speaking, betwixt those conclusions we form from cause and effect, and those that persuade us of the continued and independent existence of body. When we reason from cause and effect, we conclude, that neither colour, sound, taste, nor smell have a continued and independent existence. When we exclude these sensible qualities there remains nothing in the universe, which has such an existence.

Having found such contradictions and difficulties in every system concerning external objects, and in the idea of matter, which we fancy so clear and determinate, We shall naturally expect still greater difficulties and contradictions in every hypothesis concerning our internal perceptions, and the nature of the mind, which we are apt to imagine so much more obscure, and uncertain. But in this we should deceive ourselves. The intellectual world, though involved in infinite obscurities, is not perplexed with any such contradictions, as those we have discovered in the natural. What is known concerning it, agrees with itself; and what is unknown, we must be contented to leave so.

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 burthened 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? I 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, any one 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 every thing, 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, every thing, which is different, is distinguishable, and every thing 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 every thing 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 any thing 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 any thing 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 any one 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.