244 OPERATIONS SUBSIDIARY TO INDUCTION. 



(that it consists of individuals which have, or may 

 have, sprung from the same parents), it is presumed 

 that individuals so related resemble each other more 

 than those which are excluded by such a definition ; 

 or, perhaps, that species so defined have permanent 

 and definite differences. A definition of organization, 

 or of some other term, which was not employed to 

 express some principle, would be of no value. 



" The establishment, therefore, of a right definition 

 of a term, may be a useful step in the explication of 

 our conceptions ; but this will be the case then only 

 when we have under our consideration some proposi- 

 tion in which the term is employed. For then the ques- 

 tion really is, how the conception shall be understood 

 and defined in order that the proposition may be true.'* 



61 To unfold our conceptions by means of defini- 

 tions has never been serviceable to science, except 

 when it has been associated with an immediate use of 

 the definitions. The endeavour to define a Uniform 

 Force was combined with the assertion that gravity is 

 a uniform force : the attempt to define Accelerating 

 Force was immediately followed by the doctrine that 

 accelerating forces may be compounded: the process 

 of defining Momentum was connected with the prin- 

 ciple that momenta gained and lost are equal : natu- 

 ralists would have given in vain the definition of 

 Species which we have quoted, if they had not also 

 given the characters of species so separated. . . . 

 Definition may be the best mode of explaining our 

 conception, but that which alone makes it worth 

 while to explain it in any mode, is the opportunity of 

 using it in the expression of truth. When a defini- 

 tion is propounded to us as a useful step in know- 

 ledge, we are always entitled to ask what principle it 

 serves to enunciate,'' 



