NEW SYSTEM 317 



hypothesis has in its favour, it may be said that it is 

 something more than' a hypothesis, since it hardly 

 appears possible to explain things in any other intelli- 

 gible way, and since several great difficulties, which 

 have hitherto perplexed men's minds [les esprits], seem 

 to disappear of themselves when we rightly comprehend 

 this hypothesis. The expressions of ordinary language 

 may also be quite well adapted to it. For we may say 

 that the substance whose condition [disposition] explains 

 a change in an intelligible way (so that we may hold 

 that it is this substance to which tfre others have on this 

 point been adapted from the beginning, according to the 

 order of the decrees of God) is the substance which, in 

 respect of this change, we should consequently conceive 

 as acting upon the others 75 . Thus the action of one 

 substance upon another is not an emission nor a trans- 

 plantation of an entity as is commonly supposed, and it 

 can be rationally understood only in the way I have 

 just mentioned. It is true that we quite well conceive 

 in matter both the emission and the receiving of parts 

 through which we are entitled to explain mechanically 

 all the phenomena of physics ; but as material mass is 

 not a substance 76 , it is evident that action as regards 

 substance itself can only be what I have just said that 

 it is. 



1 8. These considerations, however metaphysical they 

 may appear, are also of remarkable service in physics 

 for establishing the laws of motion, as our Dynamics will 

 be able to show. For it may be said that in the impact 

 of bodies each suffers only through its own elasticity, 

 caused by 77 the motion which is already in it 78 . And 



7r> See Introduction, Part iii. pp. 105 sqq. 



76 See Introduction, Part iii. p. no. 



77 E. has cause du, 'a (or the) cause of the.' G-. has cause du, 

 ' caused by the.' The First Draft has : ' which comes from a motion 

 already existing in it ' (G. iv. 476). 



78 Leibniz opposes the idea that there is a fixed quantity of 

 motion dispersed throughout the universe and passing indifferently 



