CHAPTEE XXX. 



CLASSIFICATION. 



THE extensive subject of Classification has been deferred 

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

 of difficulty, and did not seem naturally to fall into an 

 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 in- 

 ference involves classification, which is indeed the necessary 

 accompaniment of the action of judgment. It is impossible 

 to detect similarity between objects without thereby joining 

 them together in thought, and forming an incipient class. 

 Nor can we bestow a common name upon objects without 

 implying the existence 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 to speak of a general notion 

 or concept is but another way of speaking of a class. Usage 

 leads us to employ the word classification in some cases 

 and not in others. We are said to form the general notion 

 parallelogram 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 

 together in a museum a number of specimens resembling- 

 each other in certain defined characters. But the logical 

 nature of the operation is the same in both cases. We 

 form a class of figures called parallelograms and we form 

 a general notion of trilobites. 



Science, it was said at the outset, is the detection of 

 identity, and classification is the placing together, either in 



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