THE MECHANICAL SYSTEM AND ITS LIMITS 379 



only half its work if it were content with these. There 

 must be subordinating concepts, expressing the common 

 element in a certain number of concepts. Thus gold, 

 silver, iron, and other minerals are grouped together as 

 " metals." As science extends its range, and looks to 

 the common element in the subordinating concepts 

 themselves, it seeks at last to pursue its method to 

 a point where it is impossible for direct observations to 

 determine the common features. Thus we not only 

 conceive the seventy elements to consist of homo- 

 geneous atoms, but also that these seventy different 

 kinds of atoms are at bottom composed of the same 

 particles, or primitive atoms [such as electrons]. The 

 diversity in the structure of the elements is due to a 

 difference in the grouping of these in the atom of the 

 element. Hence the ultimate particles make up the 

 whole material world. They are the common element 

 in all matter. 



Not only the bodies, but also the phenomena, in 

 nature are infinitely varied. When we speak of 

 "storms," we are grouping together a large number 

 of different phenomena, with respect to the common 

 feature in them. Phenomena also are grasped by 

 science through general concepts, which express the 

 common element in them. 



However, these concepts require something further. 

 They must be free from space and time, if they are 

 really to embody all that has happened, is happening, 

 or will happen, in the world. They must have a 

 universal application, because it is only then that they 



