The most fundamental of these laws is the lex continui.  On the one hand, it forbids every leap, on the other, all repetition in the series of beings and the series of events.  Member must follow member without a break and without superfluous duplication; in the scale of creatures, as in the course of events, absolute continuity is the rule.  Just as in the monad one state continually develops from another, the present one giving birth to the future, as it has itself grown out of the past, just as nothing persists, as nothing makes its entrance suddenly or without the way being prepared for it, and as all extremes are bound together by connecting links and gradual transitions,—­so the monad itself stands in a continuous gradation of beings, each of which is related to and different from each.  Since the beings and events form a single uninterrupted series, there are no distinctions of kind in the world, but only distinctions in degree.  Rest and motion are not opposites, for rest may be considered as infinitely minute motion; the ellipse and the parabola are not qualitatively different, for the laws which hold for the one may be applied to the other.  Likeness is vanishing unlikeness, passivity arrested activity, evil a lesser good, confused ideas simply less distinct ones, animals men with infinitely little reason, plants animals with vanishing consciousness, fluidity a lower degree of solidity, etc.  In the whole world similarity and correspondence rule, and it is everywhere the same as here—­between apparent opposites there is a distinction in degree merely, and hence, analogy.  In the macrocosm of the universe things go on as in the microcosm of the monad; every later state of the world is prefigured in the earlier, etc.  If, on the one side, the law of analogy follows as a consequence from the law of continuity, on the other, we have the principium (identitatis) indiscernibilium.  As nature abhors gaps, so also it avoids the superfluous.  Every grade in the series must be represented, but none more than once.  There are no two things, no two events which are entirely alike.  If they were exactly alike they would not be two, but one.  The distinction between them is never merely numerical, nor merely local and temporal, but always an intrinsic difference:  each thing is distinguished from every other by its peculiar nature.  This law holds both for the truly real (the monads) and for the phenomenal world—­you will never find two leaves exactly alike.  By the law of the conservation of force, Leibnitz corrects the Cartesian doctrine of the conservation of motion, and approaches the point of view of the present day.  According to Descartes it is the sum of actual motions, which remains constant; according to Leibnitz, the sum of the active forces; while, according to the modern theory, it is the sum of the active and the latent or potential forces—­a distinction, moreover, of which Leibnitz himself made use.