2 6 INTRODUCTION 



substance alone. These are bodily substance and think- 

 ing substance. They are mutually opposite : the one is 

 what the other is not. Neither is conditioned by the 

 other nor dependent upon it. The essential attribute 

 of bodily substance is extension, that of thinking sub. 

 stance is thought. All the specific qualities of created 

 things are reducible to one or other of these as a common 

 quality ; and consequently the essence or reality of 

 created substance comes to be either extension without 

 specific contents or thought without a specific object. 

 In other words, bodily substance is quantity of one 

 determination, namely extension ; while thinking sub- 

 stance is quantity of one other determination, namely 

 thought. Thus the presupposition of the Cartesian 

 systems is a purely quantitative relation of whole and 

 parts \ 



The same presupposition in another form underlies 

 the Atomist philosophy. The atoms are material par- 

 ticles, and the whole consists of their aggregation. If 

 the theory is self-consistent they must be regarded as 



1 Cf. Descartes, Principia, Part ii. 8 : ' Quantity and number 

 differ only in thought [ratione] from that which has quantity and 

 is numbered.' 1 1 : 'It will be easy to discern that it is the same 

 extension which constitutes the nature of body as of space, and 

 that these two things are mutually diverse only as the nature of 

 the genus and species differs from that of the individual, provided 

 we reflect on the idea we have of any body, taking a stone for 

 example, and reject all that is not essential to the nature of body. 

 In the first place, then, hardness may be rejected, because if the 

 stone were liquefied or reduced to powder it would no longer 

 possess hardness, and yet would not cease to be a body ; colour also 

 may be thrown out of account, because we have frequently seen 

 stones so transparent as to have no colour ; again, we may reject 

 weight, because we have the case of fire, which, though very light. 

 is still a body ; and finally, we may reject cold, heat, and all the 

 other qualities of this sort, either because they are not considered 

 as in the stone, or because, with the change of these qualities, the 

 stone is not supposed to have lost the nature of body. After this 

 examination we shall find that nothing remains in the idea of 

 body, except that it is something extended in length, breadth, and 

 depth ; and this something is comprised in our idea of space, not 

 only of that which is full of body, but even of what is called void 

 space' (Veitch's Tr.). Cf. Principia, Part i. 51-53, 63-65. 



