134 THE SCIENCE OF LOGIC. 



importance. The new names coined in each science avoid am 

 biguity better than ordinary names in current use. When these 

 latter are adopted as technical terms in any science, their exact 

 meaning there should be clearly set forth ; and this setting forth 

 of the technical meaning of a familiar term is one of the processes 

 described as Nominal (or Conventional] Definition (54-6). As a 

 rule, their exact meaning &quot; can be made intelligible only by pre 

 senting to the senses that which the terms are to signify. The 

 knowledge of a colour by its name can only be taught through 

 the eye. No description can convey to a hearer what we mean 

 by apple-green or French-grey. ... In order to derive due ad 

 vantage from technical terms of this kind, they must be associ 

 ated immediately with the perception to which they belong ; and 

 not connected with it through the vague usages of common 

 language [cf. 52, b\ The memory must retain the sensation ; and 

 the technical word must be understood as directly as the most 

 familiar word, and more distinctly. ... In all cases the term is 

 fixed to a peculiar meaning by convention ; and the student, in 

 order to use the word, must be completely familiar with the con 

 vention, so that he has no need to frame conjectures from the 

 word itself. Such conjecture would always be insecure, and often 



WELTON, Logic, i., chap. vi. JOSEPH, Logic, chap. v. KEYNES, Formal 

 Logic, Appendix A, pp. 441 sqq. VENN, Empirical Logic, chaps, xii., xiii. 

 MELLONE, Introductory Text-Book of Logic, chap. v. 



1 WHEWELL, op. cit. t pp. 314-5 ; apud WELTON, ibid., pp. 152-3- 



