The second difficulty is incomparably greater regarding the substantial forms and the souls of bodies, and I grant that I am not myself satisfied in regard to it. First of all, we must maintain that the bodies are substances and not merely true phenomena like the rainbow, but, on the other hand, even if this were granted, it might be inferred, I think, that the corporeal substance consists neither in extension nor in divisibility for it will be granted that two bodies distant from each other, for example, two triangles are not really one substance; suppose now that they come together to compose a square, does the mere contact make them one substance? I do not think so. Now, every extended mass may be considered as a composite of two or of a thousand others, and the only extension there is, is that by contact. Consequently, we shall never find a body of which we can say that it is really one substance; it will always be an aggregate of several. Or rather, it will not be a real being, because the component parts are subject to the same difficulty, and we should never reach a real being, for the beings which result from an aggregation have only as much reality as there is in their ingredients. Whence it follows that the substance of a body, if it has one, must be indivisible; whether we call it soul or form makes no difference to me.

The general conception of individual substance, which seems to appeal to you, M., evidences the same thing, that extension is an attribute which can never constitute a complete being; no action can ever be derived from extension, and no change. It merely expresses a present state. Never does it express the future or the past state as the conception of a substance should. When two triangles are joined, we cannot decide how this union is made, for this might happen in several ways, and whatever can have several causes is never a complete being.

Nevertheless, I acknowledge that it is very difficult to answer several question which you have put, I think we must say that if bodies or substantial forms, for example, if the beasts have souls, then these souls are indivisible. This is also the opinion of St. Thomas. Are these souls therefore indestructible? I think they are, unless it is possible that in accordance with the opinion of M. Leeuwenhoeck every birth of an animal is only the transformation of an animal already alive. There is ground, moreover, for thinking that death is also another transformation. The soul of man, however, is something more divine. It is not only indestructible but it always knows itself and continues to exist with self-consciousness. Regarding its origin, it can be said that God produced it only when this animated body, which was in the seed, determined itself to assume human form. This brute soul, which formerly animated this body before the transformation, is annihilated when the reasoning soul takes its place; or if God changes the one into the other by giving to the former a new perfection by means of an extraordinary intervention, this is a particular in regard to which I have not sufficient light.

I do not know whether the body, when the soul or substantial part is put aside, can be called a substance. It might very well be a machine, an aggregation of several substances, of such sort that if I were asked what I should say regarding the forma cadaveris or regarding a block of marble, I should say that they might perhaps be units by aggregation, like a pile of stones, but that they are not substances. The same may be said of the sun, of the earth, of machines; and with the exception of man, there is no body, of which I can be sure that it is a substance rather than an aggregate of several substances or perhaps a phenomenon. It seems to me, however, certain, that if there are corporeal substances, man is not the only one, and it appears probable that beasts have souls although they lack consciousness.

Finally, although I grant that the consideration of forms or souls is useless in special physics, it is, nevertheless, important in metaphysics. Just as geometers pay no attention to the composition of the continuum, and physicists do not ask whether one ball pushes another or whether it is God who does this.

It would be unworthy of a philosopher to admit these souls or forms without reason, but without them it is not possible to understand how bodies are substances.

XIV: Leibniz to Arnauld

Hanover, Nov. 28- Dec. 8, 1686.

Monsieur:

As I have found something very extraordinary in the frankness and in the sincerity with which you accepted certain arguments which I employed, I cannot avoid recognizing it and wondering at it. I was quite confident that the argument, based upon the general nature of propositions, would make some impression upon your mind, but I confess at the same time that there are few people able to enjoy truths so abstract whose cogency, perhaps, no one else would have been able to see so easily. I should like to be instructed by your meditations regarding the possibilities of things. They would certainly be profound and important, inasmuch as they would have to deal with those possibilities in a manner that might be worthy of God. But this will be at your convenience. As regards the two difficulties which you have found in my letter, the one regarding the hypothesis of the concomitance or of the agreement of substances among themselves, the other regarding the nature of the forms of corporeal substances, I grant that the difficulties are considerable, and if I were able to meet them entirely I should think myself able to decipher the greatest secrets of universal nature. But est aliquid prodire tenus.