270 OPERATIONS SUBSIDIARY TO INDUCTION. 



tion) would be as completely artificial and technical as the 

 Linnaean. 



Our natural groups, therefore, must often be founded not 

 on the obvious, but on the unobvious properties of things, 

 when these are of greater importance. But in such cases it is 

 essential that there should be some other property or set of 

 properties, more readily recognisable by the observer, which 

 coexist with, and may be received as marks of, the properties 

 which are the real groundwork of the classification. A natural 

 arrangement, for example, of animals, must be founded in the 

 main on their internal structure, but (as has been justly 

 remarked) it would be absurd that we should not be able to 

 determine the genus and species of an animal without first 

 killing it. On this ground, the preference, among zoological 

 classifications, is probably due to that of M. de Blainville, 

 founded on the differences in the external integuments; 

 differences which correspond, much more accurately than 

 might be supposed, to the really important varieties, both in 

 the other parts of the structure, and in the habits and history 

 of the animals. 



This shows, more strongly than ever, how extensive a 

 knowledge of the properties of objects is necessary for making 

 a good classification of them. And as it is one of the uses of 

 such a classification that by drawing attention to the proper- 

 ties on which it is founded, and which if the classification be 

 good are marks of many others, it facilitates the discovery of 

 those others ; we see in what manner our knowledge of things, 

 and our classification of them, tend mutually and indefinitely 

 to the improvement of each other. 



We said just now that the classification of objects should 

 follow those of their properties which indicate not only the 

 most numerous, but also the most important peculiarities. 

 What is here meant by importance ? It has reference to the 

 particular end in view ; and the same objects, therefore, may 

 admit with propriety of several different classifications. Each 

 science or art forms its classification of things according 

 to the properties which fall within its special cognizance, or 

 of which it must take account in order to accomplish its 



