DEFINITION. 211 



qualities on which they often depend, give that general 

 character and aspect to a set of objects, which deter- 

 mine the groups into which they naturally fall. But 

 to mount up to the more hidden agreement upon 

 which these obvious and superficial agreements de- 

 pend, is often one of the most difficult of scientific 

 problems. As it is among the most difficult, so it 

 seldom fails to be among the most important. And 

 since upon the result of this inquiry respecting the 

 causes of the properties of a class of things, there 

 incidentally depends the question what shall be the 

 meaning of a word ; some of the most profound and 

 most valuable investigations which philosophy pre- 

 sents to us, have been introduced by, and have offered 

 themselves under the guise of, inquiries into the 

 definition of a name. 



