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 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, 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 'tis impossible any thing 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.
The first notion of space and extension is derived solely from the senses of sight and feeling; nor is there anything, but what is coloured or tangible, that has parts disposed after such a manner as to convey that idea. When we diminish or increase a relish, 'tis not after the same manner that we diminish or increase any visible object; and when several sounds strike our hearing at once, custom and reflection alone make us form an idea of the degrees of the distance and contiguity of those bodies from which they are derived. Whatever marks the place of its existence, either must be extended, or must be a mathematical point, without parts or composition. What is extended must have a particular figure, as square, round, triangular; none of which will agree to a desire, or indeed to any impression or idea, except of these two senses above-mentioned. Neither ought a desire, though indivisible, to be considered as a mathematical point. For in that case 'twould be possible, by the addition of others, to make two, three, four desires; and these disposed and situated in such a manner, as to have a determinate length, breadth, and thickness; which is evidently absurd.
'Twill not be surprising after this, if I deliver a maxim, which is condemned by several metaphysicians, and is esteemed contrary to the most certain principles of human reason. This maxim is, that an object may exist, and yet be no where: and I assert, that this is not only possible, but that the greatest part of beings do and must exist after this manner. An object may be said to be no where, when its parts are not so situated with respect to each other, as to form any figure or quantity; nor the whole with respect to other bodies so as to answer to our notions of contiguity or distance. Now, this is evidently the case with all our perceptions and objects, except those of the sight and feeling. A moral reflection cannot be placed on the right or on the left hand of a passion; nor can a smell or sound be either of a circular or a square figure.
These objects and perceptions, so far from requiring any particular place, are absolutely incompatible with it, and even the imagination cannot attribute it to them. And as to the absurdity of supposing them to be no where, we may consider, that if the passions and sentiments appear to the perception to have any particular place, the idea of extension might be derived from them, as well as from the sight and touch; contrary to what we have already established. If they appear not to have any particular place, they may possibly exist in the same manner; since whatever we conceive is possible.
'Twill not now be necessary to prove, that those perceptions, which are simple, and exist no where, are incapable of any conjunction in place with matter or body, which is extended and divisible; since 'tis impossible to found a relation but on some common quality.[9] It may be better worth our while to remark, that this question of the local conjunction of objects, does not only occur in metaphysical disputes concerning the nature of the soul, but that even in common life we have every moment occasion to examine it. Thus, supposing we consider a fig at one end of the table, and an olive at the other, 'tis evident, that, in forming the complex ideas of these substances, one of the most obvious is that of their different relishes; and 'tis as evident, that we incorporate and conjoin these qualities with such as are coloured and tangible. The bitter taste of the one, and sweet of the other, are supposed to lie in the very visible body, and to be separated from each other by the whole length of the table. This is so notable and so natural an illusion, that it may be proper to consider the principles from which it is derived.