Such is an extremely brief definition of M. Renouvier's place amongst philosophers. In the volumes before us he applies the general principles of his system to the Natural Sciences, so as to trace the main lines which their speculations will have to observe. His conception of the world is a sort of monadism very much like Leibniz's, except that Leibniz's infinitism is removed, and the monads are not permanent substances but trains of representation. Real existents, in short, are psychic in nature and of various grades, and their 'intercommunication' is but our name for the fact that they form a concerted harmony, such that, when the inner states of one are modified, the inner states of others follow suit, the forms of the harmony being what we call the laws of nature. Leibniz was wrong only in speaking of the harmony as pre-established, for this word, while seeming to give a solution, really but throws the problem back, and behind the fact of the harmony we should not seek to go. The monads agree in responding to each other's changes under the forms of space and time perceptions so that the world-order appears subject to mathematical laws. Were the monads themselves only objects of outer representation like the time and space which they appear to each other to inhabit, they might be treated as indefinite in number, extent, and subdivision, for we can always go on to add to, or to divide, our own ideal objects. The moment, however, that these objects also exist as subjects, or in and for themselves, they cannot be indefinite but must be actual and numbered. If numbered, they are finite, so that all existence is discrete, and the old physical dispute between the plenum and atoms in vacua is decided categorically in favor of the latter view. Change, too, is discrete; and the world, so far as real, is like an immense pulsation composed of a number (unassignable though at all times determinate) of concerted elementary pulsations of different grades. Since the inner life of the realities is psychical, the outer view of them as atoms can only be symbolic. The atom is, in short, but our name for a point of space so far as influence appears to emanate therefrom. The 'subject' that exerts the influence need not be known to physics, so long as the definite mechanical laws of the influence can be ascertained. It is interesting to note in passing how completely the popular fancy of the atom as a hard little suprasensible body has vanished from higher physical thought. Lasswitz and Wundt, for example, use almost identical words with Renouvier in declaring the conception 'atom' to be a mere economic device like 'co-ordinate' for compendiously expressing the variations of a lot of phenomena in reference to a portion of space.
