94 INTRODUCTION 



is mere capacity for receiving motion, bare movableness, 

 while motion is complete activity and is entirely extrinsic 

 to that which is moved. Force, on the other hand, is, as we 

 have seen, something between the two, viz. a potentiality 

 f- of motion or action that is always passing into actual 

 action when it is not prevented by a similar tendency in 

 another body. This force, then, shows itself not merely 

 in actual, positive motion, but in hindrance or resistance. 

 And if this force were not of the essence of material 

 bodies there would be no resistance among bodies and 

 the absurdity of perpetual motion would be true. For if 

 material bodies consist solely of extension, and if one 

 such body moving should come into contact with another 

 at rest (i. e. destitute of motion), then the former must 

 carry the latter along with it. For, ex hypothcsi, there is 

 nothing but space to resist the progress of the moving 

 body, and, if motion is possible at all, it must be motion 

 through space, i.e. motion which mere space cannot resist 1 . 

 Accordingly, in addition to extension (however it may 

 be interpreted), eveiy material body must have resistance 

 or impenetrability. This mere passive resistance Leibniz 

 on various occasions calls avriTviria. The avTirviria of a 

 body is simply its need of space. The body is not mere 



found joined together, we cannot infer from them how the joining 

 has taken place. For it may have happened in various ways ; but 

 nothing which can have several causes is ever a concrete [accompli] 

 being.' 



1 Epistola ad Des Bosses (1706) (G. ii. 295) : 'If, with the Carte- 

 sians, we were to admit a plenum and the uniformity of matter, 

 adding only motion, it would follow that there would never be any- 

 thing in the world but a substitution of equivalents, as if the whole 

 universe were to reduce itself to the motion of a perfectly uniform 

 wheel about its axis or to the revolutions of concentric circles of 

 perfectly homogeneous matter. In that case, it would not be pos- 

 sible, even for an angel, to distinguish the state of the world at one 

 moment from its state at another moment. For there could not be 

 any variety in the phenomena. That is why, in addition to figure, 

 size, and movement, there must be admitted forms from which 

 there arises in matter a variety of appearances ; and I do not see 

 whence we can draw these forms, if they are to be intelligible, 

 except from Entelechies.' Cf. De Ipsa Natura (1693), 13 (E. 158 b ; 

 G. iv. 512). 



