POSSIBILITY OF THE ACTIVITY OF BODIES.
148. Having marked the limits of our intuitive knowledge with respect to causality and activity, it is easy to answer the objections against secondary causality, which arise from confounding intuitive and indeterminate ideas; but we have still to examine whether there are true second causes, that is, whether there really is in finite beings a principle of their own and others' changes. Some philosophers, among others the illustrious Malebranche, have denied the efficacy of second causes, thus reducing them to mere occasions. The author of theInvestigation de la Véritégoes so far as to maintain that secondary causality not only does not exist, but is impossible.
149. The universe contains two classes of beings,—immaterial beings, and corporeal beings: each presents difficulties which it will be well to examine separately. Let us begin with matter. It is said that matter is incapable of all activity, that its essence is indifferent to every thing, susceptible of any sort of modification. I cannot discover on what this general proposition is founded, nor do I seehow it is possible to prove it either by reason or by experience.
150. In order to maintain that matter is completely inactive, or incapable of any activity, it would be necessary to know its essence; but this we do not know. By what right do we deny the possibility of an attribute when we are ignorant of the nature of the object to which it should belong, when we do not know even one of its properties to which this attribute is repugnant? It is true that we deny to matter the possibility of thought, and even of sensation; but we can do so only because we know enough of matter, to establish this impossibility. In matter, whatever may be its intrinsic essence, there are parts, consequently there is multiplicity; and the facts of consciousness necessarily require a being which is one and simple.[91]
It is not the same with respect to activity; for activity, when it does not present the intuitive idea of consciousness, gives us only the indeterminate conception of a principle of changes in itself or in other beings. This does not contradict the idea of multiplicity. Suppose bodies in motion to have a true activity which really produces motion in others, there is no contradiction in this activity being distributed among the different parts of the other body, which at the moment of impact produce their respective effects, causing motion in the parts of the other body with which they come in contact.
151. Consequently, examining the questiona priori, or considering the idea of body, we can find no reason for denying the possibility of its being active. It is true that the extension of bodies, inasmuch as extension, is presented to us as something without life, indifferent to all figures and to all motions, and that we do not discover in it any principle of activity;[92]but this can prove nothing, unless we suppose that the essence of bodies consists in extension, and that extension contains nothing more than is presented to our senses, that it includes nothing on which its activity can be founded. The first is an opinion, but one without any foundation; the second can never be demonstrated, because it escapes all observation, and cannot be the object of investigationsa priori.
152. How can it be proved that the essence of bodies consists in extension?[93]What we may say is, that we experience it, and that all corporeal nature is presented to us under the form of extended. If we assert any thing more than this we do so without any foundation, we substitute for the reality a play of our fancy. The essence of any thing is that which constitutes it what it is, that which serves as the internal ground or root of the properties: who can say that we know this ground, this root, in corporeal objects? Our senses, it is true, perceive nothing not extended: we cannot conceive to what bodies would be reduced if deprived of extension; but from this we can only infer that extension is a form under which bodies are presented to our senses; that this form is a necessary condition of the affection of our sensibility; but not that the form is the essence of the thing, not that there is in the object nothing more intimate in which the form itself has its root.
153. If the essence of bodies consisted in extension, such as it appears to our senses, extension being equal there would be equality of essence; the essences of bodies might be measured like their dimensions; two globes of equal diameters, would be two essentially equal bodies. Experience, and even common sense are opposed to this. It may be said, that pure dimension, in so far as subject tomeasure, is not enough to form equality of essence; but that the equality of nature of the extension of both bodies is also requisite; but what, I ask, is the meaning of thenatureof extension? If the word nature here means any thing, it must mean something distinct from extension, in so far as subject to our sensibility; in which case I infer that just as in order to diversify the essences of bodies something is imagined which is not contained in extension in so far as subject to sensible intuition, something may in the same manner be supposed which is capable of activity, and which offers to our understanding an accessory idea giving life, so to speak, to the dead matter which we find in extension, considered as the simple object of purely geometrical ideas.
154. Experience cannot demonstrate the impossibility of the activity of bodies. Absolute inactivity cannot affect us, and therefore cannot be known by experience. We can only experience action, or the exercise of activity; inaction, or the state of an absolutely inactive thing, cannot be the object of experience without a contradiction.