CLASSIFICATION. 305 



sary 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 properties 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 mutu- 

 ally and indefinitely to the improvement of one 

 another. 



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 im- 

 portant peculiarities. What is here meant by import- 

 ance ? It has reference to the particular end in view ; 

 and the same objects, therefore, may admit with pro- 

 priety 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 accom- 

 plish its peculiar practical ends. 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 quadru- 

 peds do. But this would not prevent our speaking of 

 the whale fishery, and calling such animals fish on all 

 occasions connected with this employment; for the 



VOL. II. X 



