468 



OPERATIONS SUBSIDIARY TO INDUCTION, 



remarks) it would be absurd that we 

 should not be able to determine the 

 genus and species of an animal with- 

 out first killing it. On this ground, 

 the preference, among zoological clas- 

 sifications, is probably due to that of 

 M. de Blainville, founded on the dif- 

 ferences in the external integuments ; 

 differences which correspond much 

 more accurately than might be sup- 

 posed to the really important varieties, 

 both in the other parts of the struc- 

 ture, 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 properties on which 

 it is founded, and which, if the classi- 

 fication 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 classifi- 

 cation 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, there- 

 fore, 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 cognisance, 

 or of which it must take account in 

 order to accomplish its peculiar prac- 

 tical end. A farmer does not divide 

 plants, like a botanist, into dicotyle- 

 donous 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 paleeozoic, mesozoic, and 

 tertiary periods, above the coal and 

 below the coal, &;c. Whales are or 



I 



pose 



are not fish, according to the purposi 

 for which we are considering them. 

 " If we are speaking of the internal 

 structure and physiology of the ani- 

 mal, we must not call them fish ; for 

 in these respects they deviate widely 

 from fishes : they have warm blood, 

 and prodoce and suckle their young 

 as land quadrupeds do. But this 

 would not prevent our speaking of 

 the %ohale Jishery, and calling such 

 animals fish on all occasions connected 

 with this employment ; for the rela- 

 tions thus arising depend upon the ani- 

 mal'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 in- 

 telligent judge." * 



These different classifications are 

 all good for the purposes of their own 

 particular departments of knowledge 

 or practice. But when we are study- 

 ing objects not for any special practi- 

 cal end, but for the sake of extending 

 our knowledge of the whole of their 

 properties and relations, we must con- 

 sider as the most important attributes 

 those which contribute most, either by 

 themselves or by their effects, to ren- 

 der 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 speci- 

 ally 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 down a theory, 

 grounded on an important truth, 

 which, he has, in some respects, ex- 

 pressed and illustrated very felici- 

 tously, but also, as it appears to me, 

 with some admixture of error. It 

 will be advantageous, for both these 



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



I 



f 



I 



