The mind being often affected with sensations, during sleep, very different from those which it has experienced by the presence of the same objects, does it not lead to a belief, that the presence of objects is not necessary to the existence of our sensations; and that, of consequence, our mind and body may exist independent of those objects? During sleep, and after death, for example, our body has the same existence as before; yet the mind no longer perceives this existence, and the body with regard to us, has ceased to be. The question is therefore, whether a thing which can exist, and afterwards be no more, and which affects us in a manner altogether different from what it is, or what it has been, may yet be a reality of indubitable existence. That something exists without us, we may believe, though not with a positive assurance; whereas of the real existence of every thing within us, we have a certainty. That of our soul, therefore, is incontestable, and that of our body seems doubtful; because the mind has one mode of perception when we are awake, and another when we are asleep; after death, it will perceive by a method still more different, and the objects of its sensations, or matter in general, may then cease to exist with respect to it, as well as our bodies with which we have no further connection. But let us admit this existence of matter; and that it even exists as it appears to our senses, yet by comparing the mind with any material object, we shall find differences so great, and qualities so opposite that every doubt will vanish of the latter being of a nature totally different, and infinitely superior. The mind has but one form, which is simple, general, and uniform. Thought is this form; has nothing in it of division, extension, impenetrability, nor any other quality of matter; of consequence, therefore, our mind, the subject of this form, is indivisible, and immaterial. Our bodies on the contrary, and all other objects have many forms, each of which is compounded, divisible, variable, and perishable; and has a relation to the different organs, through which we perceive them. Our bodies, and matter in general, therefore, have neither permanent, real, nor general properties, by which we can attain a certain knowledge of them. A blind man has no idea of those objects, which sight represents to us; a leper, whose skin has lost the sense of feeling, is denied all the ideas which arise from the touch; and a deaf man has no knowledge of sounds. Let these three modes of sensation be successively destroyed, yet the mind will exist, its external functions will subsist, and thought will still manifest it within the man so deprived. But divest matter of all its qualities; strip it of colour, of solidity, and of every other property which has any relation to our senses, and the consequence will be its annihilation. Our mind, then, is unperishable, but matter may, and will perish.