LOGIC 289 



because (as in the above examples) they may be either 

 genera or species according to the way in which they 

 are used, owing to the direction taken by thought. 

 Thus the term " corporeal " is a species of the higher 

 group, the genus " substance," while it is a genus of the 

 lower group, " living creatures," which is here a species. 

 That species, however, becomes, in turn, a genus if we take 

 it in connection with ''animals" and "plants," both of 

 which are species of the genus "living creature." " Plant" 

 in turn will become a genus, whereof the species "flower- 

 ing " and " non-flowering " plants are species, and so on. 

 The attributes of the higher group, can, of course, be 

 affirmed of every member of all the lower groups which 

 are included within it, as "corporeity" can be affirmed 

 of all living creatures, all animals and all plants, and all 

 the various more and more subordinate groups of either. 

 But the higher the group, the fewer the number of 

 attributes which can be affirmed of all its component 

 members, although the larger it is, the greater the 

 number of such component members will be. On the 

 other hand, the smaller and more subordinate the group, 

 the greater the number of common characters possessed 

 by its component members. Thus the group " apple 

 tree," though it comprises almost infinitely fewer com- 

 ponent members than the group "living creatures," 

 nevertheless possesses an almost infinitely greatei 

 number of common characters than the group " living 

 creatures " possesses ; for a vastly greater number of 

 properties are common to all apple trees than are 

 common to the enormous group " living creatures," 

 which includes everything between a mushroom and a 

 man. A difference of this kind is expressed by the terms 

 extension and intension. " Extension " refers to the 

 number of groups contained within a concept ; " in- 



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