CLASSIFICATION. 271 



peculiar practical end. A farmer does not divide plants, 

 like a botanist, into dicotyledonous and monocotyledonous, 

 but into useful plants and weeds. A geologist divides fossils, 

 not like a zoologist, into families corresponding to those 

 of living species, but into fossils of the secondary and of the 

 tertiary periods, above the coal and below the coal, &c. 

 Whales are or are not fish, according to the purpose for 

 which we are considering them. "If we are speaking of the 

 internal structure and physiology of the animal, we must not 

 call them fish ; for in these respects they deviate widely from 

 fishes : they have warm blood, and produce and suckle their 

 young as land quadrupeds do. But this would not prevent 

 our speaking of the ivhale fishery, and calling such animals 

 fish on all occasions connected with this employment ; for 

 the relations thus rising depend upon the animal's living 

 in the water, and being caught in a manner similar to other 

 fishes. A plea that human laws which mention fish do not 

 apply to whales, would be rejected at once by an intelligent 

 judge."* 



These different classifications are all good, for the purposes 

 of their own particular departments of knowledge or practice. 

 But when we are studying objects not for any special 

 practical end, but for the sake of extending our know- 

 ledge of the whole of their properties and relations, we must 

 consider as the most important attributes, those which con- 

 tribute most, either by themselves or by their effects, to 

 render the things like one another, and unlike other things ; 

 which give to the class composed of them the most marked 

 individuality ; which fill, as it were, the largest space in 

 their existence, and would most impress the attention of a 

 spectator who knew all their properties but was not specially 

 interested in any. Classes formed on this principle may be 

 called, in a more emphatic manner than any others, natural 

 groups. 



3. On the subject of these groups Dr. Whewell lays 



* Nov. Org. Renov. pp. 286, 287. 



