We are thus introduced naturally to the conception which plays so large a part in the Leibnizian philosophy, that of pre-established harmony. This term simply names the fact, which we see to be fundamental with Leibniz,--the fact that, while the form of every monad is individuality, a unique principle of action, its content is universal, the very being and laws of the world. For we must now notice more explicitly what has been wrapped up in the idea all along. There is no direct influence of monads upon each other. One cannot affect another causally. There is no actual interaction of one upon another. Expressed in that figurative language which was ever natural to Leibniz, the monads have no windows by which anything can get in or out. This follows, of course, from the mutual independence and individuality of the monads. They are a true democracy, in which each citizen has sovereignty. To admit external influences acting upon them is to surrender their independence, to deny their sovereignty. But we must remember the other half. This democracy is not after the Platonic conception of democracy, in which each does as it pleases, and in which there is neither order nor law, but the extremest assertion of individuality. What each sovereign citizen of the realm of reality expresses is precisely law. Each is an embodiment in its own way of the harmony, the order, of the whole kingdom. Each is sovereign because it is dynamic law,--law which is no longer abstract, but has realized itself in life. Thus another way of stating the doctrine of pre-established harmony is the unity of freedom and necessity. Each monad is free because it is individual, because it follows the law of its own activity unhindered, unretarded, by others; it is self-determined. But it is self-determined to show forth the order, the harmony, of the universe. There is nothing of caprice, of peculiarity, in the content of the monad. It shows forth order; it is organized by law; it reveals the necessary connections which constitute the universe. The pre-established harmony is the unity of the individual and the universe; it is the organic oneness of freedom and necessity.