306 OPERATIONS SUBSIDIARY TO INDUCTION. 



relations thus arising 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 know- 

 ledge or practice. But when we are studying objects 

 not for any special practical end, but for the sake of 

 extending our knowledge of the whole of their proper- 

 ties and relations, we must consider as the most impor- 

 tant attributes, those which contribute 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 exist- 

 ence, and would most impress the attention of a 

 spectator who knew all their properties but was not 

 specially interested in any. Classes formed upon this 

 principle may be called, in a more emphatic manner 

 than any others, natural groups. 



3. On the subject of these groups Mr. Whewell 

 lays down a theory, grounded on an important truth, 

 which he has, in some respects, expressed and illus- 

 trated very felicitously; but also, as it appears to me, 

 with some admixture of error. It will be advantageous, 

 for both these reasons, to extract the statement of his 

 doctrine in the very words he has used. 



"Natural groups," according to Mr. Whewellf, 

 are " given by Type, not by Definition." And this 



* Aphorisms concerning the Language of Science, in Mr. Whe- 

 well's Philosophy of the Inductive Sciences^ vol. i., p. Ixxv. 

 t Phil Ind. Sc., i., 4767. 



