RELATION OF CORPOREAL SUBSTANCE TO ITS ACCIDENTS.
18. In the idea of corporeal substance the idea of permanence is perfectly included, the idea of unity only imperfectly. The unity which we conceive in every corporeal substance is a factitious unity; since that which is constant is not one but an aggregate of many, as is proved by the divisibility of matter; out of every corporeal substance we may make many which will have the same right as the first to be called substances. A piece of wood is a substance; but we may slit it into several pieces which will be equally substances. These pieces, joined together, formed what are calledonesubstance; but it is clear that this unity was very imperfect, and was rather a union than a unity, and that if we consider it asone, it was in relation to the unity of effect which it produced in us, by the connection which it gave to our sensations and to the phenomena which resulted from it.
19. Hence, every corporeal substance involves multiplicity, or combination of the elements which compose it. Experience informs us that this combination is not permanent; there is, consequently, no corporeal substance which does not imply at least one modification, namely, the arrangement of its parts. Abstracting the changes which this modification may undergo, it can never be confounded with the substance: although the bodies might be presented constantly to our senses with the same arrangement of the parts, the permanentbeingwould be in the parts, not in their arrangement. The latter is something external which is added to the thing existing; there can be no union and combination without parts which are united and combined.
20. A difference which we observe between the substance and its modifications is, that the substance is independent of the modifications, but the modifications are not independent of the substance. The substance, while remaining the same, changes its accidents, but an accident cannot change its substance and remain the same. The same block may receive different figures successively; but a figure, numerically the same, cannot pass from one block to another. Two blocks may have a similar or a different figure, whether cubic, spherical, or pyramidal, and one may take the figure of the other; but in that case, the figures are not identical, but similar, they are specifically but not numerically the same.
21. If I am asked how I know that there is only similarity and not numerical identity in the figures which bodies take successively, that there is nopermanencein the figures which change their subject, and consequently that the same figure cannot pass from one substance to another, in the same manner that the same substance passes from one figure to another; I shall not find it difficult to prove what I assert.
There is no one who does not see what an extravagant thing it would be for a cubic figure to leave a body and pass to another. What is this figure separated from the body? How is it preserved during the transition? Why is it not exactly the same in both, but presented with slight modifications? Has it undergone a modification in its passage from one body to another? Then there would be a modification of a modification, and the figure in itself abstracted from all body, would be a kind of substance of a secondary order, permanent under modifications. These are but absurd dreams in which that is applied to the concrete which belongs to the idea only in the abstract. This transition of the forms would suppose their separate existence, and thus we might have all kinds of abstract figures, cubes, spheres, circles, triangles, etc., subsisting in themselves without application to any thing figured.
22. A still stricter demonstration of this truth is possible. If we suppose a figure, numerically the same, to pass from one body to another; the block A, which loses the cubic form, transmits it to the body B. Now, this individual form cannot be in both at the same time. Suppose that after the cubic form has left the block A, we turn it back before it has touched the body B, evidently it will not be the same in both: therefore the body B has not acquired the same, but only a similar form. It is also evident that in order to give the cubic form, we need not take it from another; therefore, the form of one is notindividuallythat of the other; otherwise we should have to say that it is and is not, that it is preserved and ceases to exist at the same time.
23. The termtransmissionorcommunicationof motion, which is so much used in physical science, expresses something real so long as limited to the phenomenon which is under calculation; but it would be an absurdity, if itmeant that thesamemotion which was in one body haspassedto another. The sum of the quantities of motion is the same in elastic bodies after impact as before it; the velocity being divided between them, and the one gaining what the other loses. This is proved by calculation, and confirmed by experience. But it is evident that one body does not impart thesameindividual velocity which it contained to the other body; for not only can the velocity not be separated from the body and pass from one subject to another; but it cannot even be conceived except as a relation, the idea of which includes the ideas of a body moved, of space, and of time. It is true that Q representing the quantity of the motion before impact, the value of Q remains the same after impact; but this only expresses the phenomenon in relation to its effects, as subject to calculation; not that the velocity in the second member of the equation is composed of the parts of the first. Let A and B represent two bodies, the individual masses of which are expressed by these two letters; and V,vtheir respective velocities before impact. The quantity of motion will be Q = A × V + B ×v. After impact there will be a new velocity which we may callw, and the quantity of motion will be Q = A ×w+ B ×u. Mathematically speaking, the value of Q will be the same; but this only means that if the results of the motion be expressed in lines or numbers, we shall have the same after impact as before it; it does not and cannot mean that in the velocityu, considered as united to the subject, there is a portion of velocity which has been detached from V to be joined tov.
24. Hence, we do not conceive the accidents of bodies as possible without a subject in which they are inherent; and that substances are not inherent in another being, but are conceived and really exist without this inherence. A figure cannot exist without a thing figured, but the thingfigured may still exist, through all other things are destroyed. The analysis of the nature of substance shows that its existence supposes the existence of another being which produced it; but relation between them is that of cause and effect, not of inherence, or that of the subject and its modification.
25. These last observations explain another mark of corporeal substances. In the third chapter of this book we found the three characteristics of being, the relation of the permanent to the variable, and the subject of the variations; we now find a fourth, which is a negation, non-inherence in another. This negative characteristic is included in the positive one,permanent subject of variations; for it is clear that in conceiving a subjectpermanent amid variationswe do not include inherence, but rather deny it, at least implicitly. Non-inherence supposes something positive, something on which is founded the denial of the necessity of being inherent. What is this something? We know not. We know that it exists, but its explanation is beyond our reach. It is probably inexplicable without the intuition of the essence of things;—an intuition which we have not.