CLASSIFICATION. 275 



given number of definite properties, plus the effects which 

 follow from those properties, but running through the whole 

 nature, through the attributes generally, of the things so dis- 

 tinguished. Our knowledge of the properties of a Kind is 

 never complete. We are always discovering, and expecting to 

 discover, new ones. Where the distinction between two classes 

 of things is not one of Kind, we expect to find their properties 

 alike, except where there is some reason for their being diffe- 

 rent. On the contrary, when the distinction is in Kind, we 

 expect to find the properties different unless there be some 

 cause for their being the same. All knowledge of a Kind 

 must be obtained by observation and experiment upon the 

 Kind itself; no inference respecting its properties from the 

 properties of things not connected with it by Kind, goes for 

 more than the sort of presumption usually characterized as an 

 analogy, and generally in one of its fainter degrees. 



Since the common properties of a true Kind, and conse- 

 quently the general assertions which can be made respecting 

 it, or which are certain to be made hereafter as our know- 

 ledge extends, are indefinite and inexhaustible; and since 

 the very first principle of natural classification is that of 

 forming the classes so that the objects composing each may 

 have the greatest number of properties in common ; this 

 principle prescribes that every such classification shall recog- 

 nise and adopt into itself all distinctions of Kind, which 

 exist among the objects it professes to classify. To pass 

 over any distinctions of Kind, and substitute definite dis- 

 tinctions, which, however considerable they may be, do not 

 point to ulterior unknown differences, would be to replace 

 classes with more by classes with fewer attributes in common ; 

 and would be subversive of the Natural Method of Classi- 

 fication. 



Accordingly all natural arrangements, whether the reality 

 of the distinction of Kinds was felt or not by their framers, 

 have been led, by the mere pursuit of their own proper end, 

 to conform themselves to the distinctions of Kind, so far as 

 these had been ascertained at the time. The Species of 



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