Though so much interested in acquiring a thorough knowledge of ourselves, yet I do not know if man is not less acquainted with the human, than with any other existence. Provided by nature with organs, calculated solely for our preservation, we only employ them to receive foreign impressions. Intent on multiplying the functions of our senses, and on enlarging the external bounds of our being, we rarely make use of that internal sense which reduces us to our true dimensions, and abstracts us from every other part of the creation. It is, however, by a cultivation of this sense alone that we can form a proper judgment of ourselves. But how shall we give it its full activity and extent? How shall the soul, in which it resides, be disengaged from all the illusions of the mind? We have lost the habit of employing this sense; it has remained inactive amidst the tumult of our corporeal sensations, and dried up by the heat of our passions; the heart, the mind, the senses, have all co-operated against it.
Unalterable in its substance, and invulnerable by its essence, it still, however, continues the same. Its splendor has been overcast, but its power has not been diminished: it may be less luminous, but its guidance is not the less certain. Let us then collect those rays, of which we are not yet deprived, and its obscurity will decrease; and though the road may not in every part be equally filled with light, we yet shall have a torch that will prevent us from going astray.
The first and most difficult step which leads to the knowledge of ourselves, is a distinct conception of the two substances that constitute our being. To say simply, that the one is unextended, immaterial, and immortal, and that the other is extended, material, and mortal, is only to deny to the one, what we affirm the other possesses. What knowledge is to be acquired from this mode of negation? Such negative expressions can exhibit no positive ideas: but to say that we are certain of the existence of the former, and that of the latter is less evident; that the substance of the one is simple, indivisible, and has no form, since it only manifests itself by a single modification, which is thought; that the other is a less substance than a subject, capable of receiving different forms, which bear a relation to our senses, but are all as uncertain and variable as the organs themselves; that is to say something; it is to ascribe to each such distinct and positive properties as may lead us to an elemental knowledge of both, and to a comparison between them.
From the smallest reflection on the origin of our knowledge, it is easy to perceive that it is by comparison alone we acquire it. What is absolutely incomparable, is utterly incomprehensible; of this God is the only example; he exceeds all comprehension, because he is above all comparison. But whatever is capable of being compared, contemplated, and considered relatively, in different lights, may always come within the sphere of our understanding. The more subjects of comparison we have for examining any object, the more methods there are for obtaining a knowledge of it, and with greater facility.
The existence of the soul is fully demonstrated. To be and to think are with us identically the same. This truth is more than intuitive; it is independent of our senses, of our imagination, of our memory, and of all our other relative faculties. The existence of our bodies, and of external objects, is however held in uncertainty by every unprejudiced reasoner; for what is that extension of length, breadth, and thickness, which we call our body, and which seems to be so much our own, but as it relates to our senses? What are even the material organs of those senses, but so many conformities with the objects that affect them? And with regard to our internal sense, has it any thing similar or in common with these external organs? Have the sensations excited by light or sound any resemblance to that tenuous matter, which seems to diffuse light, or to that tremulous undulation, which sound produces in the air? The effects are certainly produced by the necessary conformity there is between the eyes and ears, and those matters which act upon them. Is not that a sufficient proof, that the nature of the soul is different from that of matter?
It is then a certain truth, that the internal sensation is altogether different from its cause; as also, if external objects exist, they are in themselves very different from what we conceive them. As sensation therefore bears no resemblance to the thing by which it is excited; does it not follow, that the causes of our sensations, necessarily differ from our ideas of them? The extension which we perceive by our eyes, the impenetrability, of which we receive an idea by the touch in all those qualities, whose various combinations constitute matter, are of a doubtful existence; since our internal sensations of extension, impenetrability, &c. are neither extended nor impenetrable, and have not even the smallest affinity with those qualities.
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.