4O INTRODUCTION 



'void' in the older Atomism. Each is the necessary 

 correlative of the indivisible and impenetrable elements. 

 The conception of continuity, however, by implying 

 a plenum, escapes the contradictions that are involved 

 in the idea of a void. But it has still to be shown how 

 change is possible within a plenum, or how change can 

 take place without disturbing the continuity of the 

 infinite series of Monads. Any change within a plenum 

 affects eveiy part of it. This is the principle involved 

 in the scientific point of view regarding the universe, 

 which became current with the rise of modern philosophy. 

 Everything in the world acts and reacts upon everything 

 else. However separate things may be, no change can 

 take place in any one without affecting every other. The 

 influence may in some cases be imperceptible, infinitely 

 , small; but it exists. If, however, the universe be a 

 quantitative plenum, it is impossible to understand how 

 any change could originate within it. It must receive its 

 motion from outside, and must thus be regarded as finite, 

 which again is inconsistent with its reality as a plenum. 

 Leibniz overcomes this difficulty by regarding the uni- 

 verse, not as an infinite mass occupying all that there is 

 to occupy, but as a continuity or infinite gradation of 

 ^J fjtplitntiVe differences., each containing within itself the 

 principle of its own changes. He substitutes for an 

 extensive plenum of mass an intensive continuum of force 

 or life. 



But if the universe consists of an infinity of Monads, 

 each independent of the rest, impenetrable and unaffected 

 by them, and each containing within itself the principle 

 of all its changes, how is it possible for a change to take 

 place in any one of them without destroying the con- 

 tinuity of the series 1 ? Each Monad contains within 



1 How the perfect independence of the Monads is to be reconciled 

 with the continuity of their series is a question which Leibniz does 

 not answer. For him the ideal unity of the Monads (as each repre- 

 senting the same universe) does not make their mutual indepen- 

 dence any the less complete. To give up the independence of the 



