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. We now turn from the formal framework of general laws, to the actual, to that which, obeying these laws, constitutes the living content of the world. %2. The Organic World.% A living being is a machine composed of an infinite number of organs. The natural machines formed by God differ from the artificial machines made by the hand of man, in that, down to their smallest parts, they consist of machines. Organisms are complexes of monads, of which one, the soul, is supreme, while the rest, which serve it, form its body. The dominant monad is distinguished from those which surround it as its body by the greater distinctness of its ideas. The supremacy of the soul-monad consists in this one superior quality, that it is more active and more perfect, and clearly reflects that which the body-monads represent but obscurely. A direct interaction between soul and body does not take place; there is only a complete correspondence, instituted by God. He foresaw that the soul at such and such a moment would have the sensation of warmth, or would wish an arm-motion executed, and has so ordered the development of the body-monads that, at the same instant, they appear to cause this sensation and to obey this impulse to move. Now, since God in this foreknowledge and accommodation naturally paid more regard to the perfect beings, to the more active and more distinctly perceiving monads than to the less perfect ones, and subordinated the latter, as means and conditions, to the former as ends, the soul, prior to creation, actually exercised an ideal influence--through the mind of God--upon its body. Its activity is the reason why in less perfect monads a definite change, a passion takes place,