250 OPERATIONS SUBSIDIARY TO INDUCTION. 



vention ; and the student, in order to use the word, must he 

 completely familiar with the convention, so that he has no 

 need to frame conjectures from the word itself. Such con- 

 jectures would always be insecure, and often erroneous. Thus 

 the term papilionaceous applied to a flower is employed to 

 indicate, not only a resemblance to a butterfly, but a resem- 

 blance arising from five petals of a certain peculiar shape 

 and arrangement ; and even if the resemblance were much 

 stronger than it is in such cases, yet, if it were produced in a 

 different way, as for example, by one petal, or two only, in- 

 stead of a ' standard,' two * wings,' and a ' keel ' consisting of 

 two parts more or less united into one, we should be no longer 

 justified in speaking of it as a 'papilionaceous ' flower." 



When, however, the thing named is, as in this last case, 

 a combination of simple sensations, it is not necessary, in 

 order to learn the meaning of the word, that the student should 

 refer back to the sensations themselves ; it may be com- 

 municated to him through the medium of other words ; the 

 terms, in short, may be defined. But the names of elementary 

 sensations, or elementary feelings of any sort, cannot be 

 defined ; nor is there any mode of making their signification 

 known but by making the learner experience the sensation, 

 or referring him, through some known mark, to his remem- 

 brance of having experienced it before. Hence it is only the 

 impressions on the outward senses, or those inward feelings 

 which are connected in a very obvious and uniform manner 

 with outward objects, that are really susceptible of an exact 

 descriptive language. The countless variety of sensations 

 which arise, for instance, from disease, or from peculiar phy- 

 siological states, it would be in vain to attempt to name ; for 

 as no one can judge whether the sensation I have is the same 

 with his, the name cannot have, to us two, real community of 

 meaning. The same may be said, to a considerable extent, 

 of purely mental feelings. But in some of the sciences which 

 are conversant with external objects, it is scarcely possible to 

 surpass the perfection to which this quality of a philosophical 

 language has been carried. 



