DEFINITION OF CORPOREAL SUBSTANCE.
13. What is the permanent subject of transformations in the sensible order? Is it a pure illusion? Is it a reality? What reality can it be? Does it not seem rather an abstraction? A thing which is no color, but lends itself all colors; which is none of the qualities which we experience, but the subject and cause of them all; which is no form, but accommodates itself to all forms; which is not pure extension, because this is an abstraction, and it is something which serves as the ground of other things; a corporeal object which, in itself, can affect none of the senses; what is it? Is it what the Aristotelians call an occult quality, a mysterious, and fantastic being, a mere illusion? Let us examine it by the light of experience.
14. Let us take a piece of wax and without letting it go out of our hands paint it different colors successively, subject it to different degrees of temperature, softening it by warming, and then cooling it; let us give it different forms, of a globe, a cylinder, a parallelopipedon, a table, a vase, or a statue; do all these changes take place in the same thing? Yes. Is this thing not a color, or a figure, or a degree of temperature? No; because all these qualities were and ceased to be whilst the thing remained the same. How do I know that the thing remained the same? Because there was a continuity of sensation in the eye fixed upon the object; in the touch which, although it felt the modifications of warm and cold, hard and soft, experienced also an uninterrupted sensation of an object, which remained constantly in the hand, and the weight of which was continuously felt. Therefore there is something therewhich is not the modifications, but is that which is modified, something common to them all, which receives and connects them, outside of me and within me.
15. Examining one conception of this permanent something, we find that, after abstracting its qualities, we have:
I. The idea of being. We say the thing, the something, the subject, etc., we therefore speak of a being, of a quality. Without the reality there is nothing; and nothing cannot be the subject of modifications, or the link connecting impressions.
II. The idea of being, which we here find, is not pure, it is not being alone. The qualities exist, are beings, and still we do not confound them with the subject.
III. That which accompanies the idea of being is the idea of permanence amidst succession, and the relation of this permanence as the point of connection, the immovable centre in the midst of succession.
16. If, therefore, we wished to define substance, we could only say that it isa permanent being in which occur the changes which are presented to us in the sensible phenomena. Our knowledge is all reduced to this; all that we can add beside, is only hypothesis or conjecture. In vain you ask me, what is this being? Give me the intuition of the essence of corporeal things, and I will tell you; but while I know them only by their effects, that is, the impressions which they produce in me, I cannot answer you. I know that it is something; I know its relation to its forms; I know that the forms are in the subject, and are not the subject; but here is the limit of my knowledge. The object corresponding to the idea composed of a permanent being and its relation to various forms is what I call corporeal substance.
17. Since the substance changes its accidents, remaining the same itself, it follows that its existence is independentof the accidents. Abstracting, for the present, whether it can or cannot exist without any, I only affirm that none in particular is necessary to it. Here we must take note of the difference between substance in itself, and in the medium by which it is manifested to us, and placed in active or passive communication with us. The accidents are this medium; they are the transitory forms it puts on. How can we know the existence of bodies, except by sensations? The object of sensation is not substance in its inner nature, but only its qualities as affecting us.