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.