224 OPERATIONS SUBSIDIARY TO INDUCTION. 



a first-rate authority) have thought that no other property so 

 well answers the conditions required for the definition. 



5. Having laid down the principles which ought for 

 the most part to be observed in attempting to give a precise 

 connotation to a term in use, I must now add, that it is not 

 always practicable to adhere to those principles, and that even 

 when practicable, it is occasionally not desirable. 



Cases in which it is impossible to comply with all the 

 conditions of a precise definition of a name in agreement with 

 usage, occur very frequently. There is often no one connota- 

 tion capable of being given to a word, so that it shall still 

 denote everything it is accustomed to denote; or that all 

 the propositions into which it is accustomed to enter, and 

 which have any foundation in truth, shall remain true. Inde- 

 pendently of accidental ambiguities, in which the different 

 meanings have no connexion with one another; it continually 

 happens that a word is used in two or more senses derived 

 from each other, but yet radically distinct. So long as a term 

 is vague, that is, so long as its connotation is not ascertained 

 and permanently fixed, it is constantly liable to be applied by 

 extension from one thing to another, until it reaches things 

 which have little, or even no, resemblance to those which 

 were first designated by it. 



Suppose, says Dugald Stewart, in his Philosophical 

 Essays,* " that the letters A, B, C, D, E, denote a series of 

 objects; that A possesses some one quality in common with 

 B; B a quality in common with C; C a quality in common 

 with D ; D a quality in common with E ; while at the same 

 time, no quality can be found which belongs in common to 

 any three objects in the series. Is it not conceivable, that the 

 affinity between A and B may produce a transference of the 

 name of the first to the second ; and that, in consequence of 

 the other affinities which connect the remaining objects to- 

 gether, the same name may pass in succession from B to C ; 

 from C to D ; and from D to E ? In this manner, a common 



* P. 217, 4 to edition. 



