352 THE PRINCIPLES OF SCIENCE. 



ance of a resemblance is to be determined, nor what is 

 the measure of the closeness of analogy. Until all the 

 words employed in a definition are made clear in meaning, 

 the definition itself is worse than useless. Now if the 

 views concerning classification here upheld are true, there 

 can be no sharp and precise distinction between natural 

 and artificial systems. Ah 1 arrangements which serve any 

 purpose at all must be more or less natural, because, if 

 closely enough scrutinized, they will involve more resem- 

 blances than those whereby the class was defined. 



It is true that in the biological sciences there would be 

 one arrangement of plants or animals which would be 

 conspicuously instructive, and in a certain sense natural, 

 if it could be attained, and it is that after which natural- 

 ists have been in reality striving for nearly two centuries, 

 namely, that arrangement which would display the genea- 

 logical descent of every form from the original life germ. 

 Those morphological resemblances upon which the classi- 

 fication of living beings is almost always based are in- 

 herited resemblances, and it is evident that descendants 

 will usually resemble their parents and each other in a 

 great many points. 



I have said that a natural is distinguished from an 

 arbitrary or artificial system only in degree. It will be 

 found almost impossible to arrange objects according to 

 any one circumstance without finding that some correla- 

 tion of other circumstances is thus made apparent. No 

 arrangement could seem more arbitrary than the common 

 alphabetical arrangement according to the initial letters 

 of the name. But we cannot scrutinize a list of names 

 of persons without noticing a predominance of Evans's 

 and Jones's, under the letters E and J, and of names 

 beginning with Mac under the letter M. The predomi- 

 nance is so great that we could not attribute it to chance, 

 and inquiry would of course show that it arose from im- 



