284 OPERATIONS SUBSIDIARY TO INDUCTION. 



without being distracted by thinking unnecessarily of 

 the parts of which S is itself composed. 



But there is another reason, in addition to that of 

 promoting perspicuity, for giving a brief and compact 

 name to each of the more considerable results of ab- 

 straction which are obtained in the course of our 

 intellectual phenomena. By naming them, we fix our 

 attention upon them; we keep them more constantly 

 before the mind. The names are remembered, and 

 being remembered, suggest their definition; while if 

 instead of specific and characteristic names, the meaning 

 had been expressed by putting together a number of 

 other names, that particular combination of words 

 already in common use for other purposes would have 

 had nothing to make itself remembered by. If we 

 want to render a particular combination of ideas 

 permanent in the mind, there is nothing which 

 clenches it like a name specially devoted to express 

 it. If mathematicians had been obliged to speak of 

 " that to which a quantity, in increasing or diminishing, 

 is always approaching nearer, so that the difference 

 becomes less than any assignable quantity, but to 

 which it never becomes exactly equal," instead of 

 expressing all this by the simple phrase, " the limit of 

 a quantity," we should probably have long remained 

 without most of the important truths which have 

 been discovered by means of the relation between 

 quantities of various kinds and their limits. If 

 instead of speaking of momentum, it had been necessary 

 to say " the product of the number of units of velo- 

 city in the velocity by the number of units of mass in 

 the mass," many of the dynamical truths now appre- 

 hended by means of this complex idea, would probably 

 have escaped notice for want of recalling the idea 

 itself with sufficient readiness and familiarity. And on 



