82 THE LIMITATIONS OF SCIENCE 



are real and objective to us. However, by such a proc- 

 ess we do not obtain a knowledge of things themselves, 

 but only of their attributes. Hence, the final reality 

 must be those attributes which are inseparable from our 

 conception of all phenomena, and there should be 

 some one essential attribute which may be used to 

 designate things in general. Thus hardness, while it is 

 an attribute, is not essential, for a body moving at 

 the same speed as ourselves does not give us the sensa- 

 tion of hardness. After careful consideration he found 

 that simple extent in length, breadth, and thickness is 

 the one attribute common and essential to all mat- 

 ter. Not only is this true, but the extent of matter is 

 identical with the extent of space : " The same extent in 

 length, breadth, and thickness, which constitutes space, 

 constitutes a body; and the difference between them 

 lies in this, that we attribute to a body a particular and 

 limited extent which changes position with the body as 

 it moves, and that we attribute to space an extent so 

 general and so vague that when we remove from a cer- 

 tain space the body which occupied it we do not think 

 we have transported the extent with it ; meanwhile the 

 extent of the body remains of the same size, of the 

 same figure, and has changed position with respect to 

 the body only as we determine position by other 

 bodies." 



The reason, according to Descartes, why we have 

 been led to believe that substance is different from 



