CHAPTER XXX. 



CLASSIFICATION. 



THE extensive subject of Classification lias been deferred 

 to a late part of this treatise, because it involves many 

 questions of difficulty, and did not seem naturally to fall 

 into any earlier place. But it must not be supposed that, 

 in now formally taking up the subject, we are for the first 

 time entertaining the notion of classification. All logical 

 inference involves classification, which is indeed the neces 

 sary accompaniment of the action of judgment. It is 

 impossible to detect a point of similarity between two or 

 more objects without thereby joining them together in 

 thought, and thus forming an incipient or potential class. 

 Nor can we ever bestow a common name upon two or 

 more objects without thereby equally implying the exis 

 tence of a class. Every common name is the name of 

 a class, and every name of a class is a common name. It 

 is evident also that every general notion, or concept is but 

 another way of speaking of a class. Usage alone leads us 

 to use the word classification in some cases and not in 

 others. We are said to form the general notion parallelo 

 gram when we regard an infinite number of possible four- 

 sided rectilinear figures as resembling each other in the 

 common property of possessing parallel sides. We should 

 be said to form a class, Trilobite, when we place alongside 

 of each other in a museum a number of hand specimens 

 resembling each other in certain defined qualities. But 



