XXX.] CLASSIFICATION. 701 



Siunwium Genvs and Infima Species. 



As a genus means any class whatever which is regai'ded 

 as composed of minor classes or species, it follows that the 

 same class will be a genus in one point of view and a 

 species in another. Metal is a genus as regards alkaline 

 metal, a species as regards element, and any extensive 

 system of classes consists of a series of subordinate. Or as 

 they are technically called, sichahern genera and species. 

 The question, however, arises, whether such a chain of 

 classes has a definite termination at either end. The 

 doctrine of the old logicians was to the effect that it termi- 

 nated upwards in a genus generalissimicm ot sumnium genus, 

 which was nob a species of any wider class. Some very 

 general notion, such as substance, object, or thing, was 

 supposed to be so comprehensive as to include all thinkable 

 objects, and for all practical purposes this might be so. 

 But as T have already explained (p. 74), we cannot really 

 tliink of any object or class without thereby separatiiig it 

 from what is not that object or class. AH thinking is 

 relative, and implies discrimination, so that every class 

 and every logical notion must have its negative. If so, 

 there is no such thing as a smnmum genus ; for we cainiot 

 frame the requisite nution of a class forming it without 

 implying the existence of another class discriminated from 

 it ; add this new negative class to the supposed suvnnuvi 

 yenus, and we form a still higher genus, wdiicli is absurd. 



Although there is no absolute summum genus, neverthe- 

 less relatively to any branch of knowledge or any particular 

 argument, there is always some class or notion which bounds 

 our horizon as it were. The chemist restricts his view to 

 material sul)stances and the forces manifested in them ; 

 the mathematician extends his view so as to comprehend 

 all notions capal)le of numerical discrimination. The biolo- 

 gist, on the other hand, lias a narrower sphere containing 

 only organised bodies, and of these the botanist and the 

 zoologist take parts. In other subjects there may be a 

 still narrower summum genus, as when the lawyer regards 

 only reasoniii'f beings of his own country together with 

 their jtrnperty. 



In tlie description of the Logical Al]ihabet it was pointed 

 out (p. 93) that every series of condu nations is really the 



