4. There is thus no danger of dissolution, and there is no conceivable way in which a simple substance can perish naturally.
5. For the same reason, there is no way in which a simple substance can begin naturally, since it could not be formed by composition.
6. Therefore we may say that the Monads can neither begin nor end in any other way than all at once; that is to say, they cannot begin except by creation, nor end except by annihilation; whereas that which is compounded, begins and ends by parts.
7. There is also no intelligible way in which a Monad can be altered or changed in its interior by any other creature, since it would be impossible to transpose anything in it, or to conceive in it any internal movement—any movement excited, directed, augmented or diminished within, such as may take place in compound bodies, where there is change of parts. The Monads have no windows through which anything can enter or go forth. It would be impossible for any accidents to detach themselves and go forth from the substances, as did formerly the Sensible Species of the Schoolmen. Accordingly, neither substance nor accident can enter a Monad from without.
8. Nevertheless Monads must have qualities—otherwise they would not even be entities; and if simple substances did not differ in their qualities, there would be no means by which we could become aware of the changes of things, since all that is in compound bodies is derived from simple ingredients, and Monads, being without qualities, would be indistinguishable one from another, seeing also they do not differ in quantity. Consequently, a plenum being supposed, each place could in any movement receive only the just equivalent of what it had had before, and one state of things would be indistinguishable from another.
9. Moreover, each Monad must differ from every other, for there are never two beings in nature perfectly alike, and in which it is impossible to find an internal difference, or one founded on some intrinsic denomination.
10. I take it for granted, furthermore, that every created being is subject to change—consequently the created Monad; and likewise that this change is continual in each.
11. It follows, from what we have now said, that the natural changes of Monads proceed from an internal principle, since no external cause can influence the interior.
12. But, besides the principle of change, there must also be a detail of changes, embracing, so to speak, the specification and the variety of the simple substances.
13. This detail must involve multitude in unity or in simplicity: for as all natural changes proceed by degrees, something changes and something remains, and consequently there must be in the simple substance a plurality of affections and relations, although there are no parts.