APPLICATION OF THE IDEA OF SUBSTANCE TO CORPOREAL OBJECTS.
7. Let us apply the ideas contained in that of substance to a corporeal object: this will help explain these ideas, and perhaps suggest others.
The paper on which I am writing is susceptible of various modifications: I may write on it a thousand different things,in various characters, and in different colors; I may fold it in various ways, and give it an infinite variety of positions in relation to the objects around it, and I may move it in all imaginable directions. Under this infinity of changes there is something constant, something which does not change. There are many new things, but there is one which is not new, which is always the same. There is one which suffers these changes, but retains something which does not change. If I make the paper blue and then red, that which is now red is the same that was blue, and before that white, and to this which is constant all those changes are referred. If a white paper is shown me, and then another paper that is blue, and then one that is red, it is clear that it is not the same as though I gave all these transformations to the same paper. The impression which the color produces in me remains the same; in what, then, does the difference consist? The difference is, that in the one case there is something permanent, which has passed through successive changes; in the other case thissomethingis not the same, but is another and different thing. In the one case there are different modifications; in the other there are different substances.
8. Let us go deeper into the matter. If we only received the successive impressions without any means of referring them to the same object, to connect them in a common point, we should find no difference between the two cases of which we have been speaking. If a piece of white paper be placed before us, and, after turning our eyes aside for a moment, we find a blue paper in the same place, with the same dimensions, and after again turning our eyes aside we find a red paper: it is clear that it would be impossible for us to distinguish, by the mere succession of the visual impressions, whether the same paper has been differently colored in succession, or different papers have been substituted for the first. But if we keep our eyes on the place where the paper is, we see whether the paper is colored or changed. In the first case, the appearance of the new color will continue with the same sensation of the paper, unmoved, the transformation is made without our losing sight of it, and the paper receives the continued succession of its motions and positions under the hand of the one who colors it. We are then sure that the paper is the same, because there has been a continuity of sensation, or rather a connection of the different colors with a third, resulting from the situation of the paper and its motions, and from all that by which we know what is common to the first and the second. But if there is no new coloring of the paper, but a substitution of a differently colored paper, we see that the first paper is taken away; the whole order of the sensation is interrupted, and new sensations are presented. These last have no connection with the first; there is, consequently, for us a differentthing.
9. This shows how the idea of substance with respect to bodies is generated in us, or, to speak more properly, how we apply the idea of substance to bodies. When we discover a link which unites the different sensations in one point, we call that in which they are united, substance. And as we meet in nature with many of these points which are independent of one another, we naturally say there are many corporeal substances.
10. When we perceive an impression we never call it a substance, if we refer it to an object, or consider it as objective: for the object is not, of itself alone, capable of connecting various sensations. We receive the sensations of red, and not only ordinary people, but even philosophers, when not philosophizing, make the color objective, and consider the red, not as a simple sensation, but as an external quality. No one would call this quality by itself asubstance; for it is not capable, of itself alone, of connecting other impressions or qualities. If there is a change of color the red disappears, and the new impression is connected in the order of time with the sensation of the red, but does not reside in it. If there is a change of form, although the red continues, we do not conceive this color as the necessary link between the two forms, because we know that the continuance of the red is indifferent to the variety of form, which may be changed with or without the continuance of this color.
As in general we have experienced that no sensation is necessarily connected with another, and that among sensations connected at a common point, some disappear without the rest disappearing, we infer that none of them is a necessary link; and therefore, although we make them objective, we do not give them the character of a substance, of any thing remaining identical through changes, of which it is, as it were, the recipient.
11. There is a property in bodies which is necessary to all sensations, or at least, to the two principal sensations of sight and touch. This property is extension, which, whether considered subjectively or objectively, we regard as a recipient of all sensations. We neither see nor imagine the white or black; we neither touch nor imagine the hard or the soft, the warm or the cold, without the extension in which the whiteness or blackness, the hardness or softness, the warmth or the cold reside. Thus extension might perhaps merit the honor of substance, if it were not subject to another condition, which deprives it of this title.
Although when we conceive extension in general, in the abstract, considering it as a mere continuity, we absolutely abstract it from all form; when we have need of an applied extension as the recipient of sensations, it is impossible to find it without a determinate form and figure. We do notsee a color simply, but we see it in a circular, triangular, or other extension. These forms are confounded with extension itself as its applications; and do not serve as a link for other sensations. Sometimes, it is true, the same figure receives different colors, different positions, different degrees of heat or cold, etc., but the contrary also sometimes occurs, and with the same color, and the same degree of heat or cold, with the same continuance of the other sensations, the object changes its form; just as a red circle may become a green circle, a red object may become circular, and afterwards triangular. In the first case, the circular figure is the link connecting the sensations of the colors; in the second, the color is the link connecting the figures.
12. Having deprived extension of the honor of substance, as well as all other sensations, in so far as objective; we may observe that all these variations in the objects are successive, and the sensations are connected with each other. Thus the same circle may take different colors; and the same color different figures; the colors may be again changed, and the first reproduced, the figure remaining the same; or the first figure may be reproduced, the colors remaining the same. We conclude that under this variety there is something constant, that under this multiplicity there is something which is one; that under this succession of being and not-being there is something permanent; and this which is constant, one, and permanent, the recipient of these changes, the point outside of us which connects them, and enables us to conceive them connected,—this is what we call substance.