DEFINITION. 95 



concepts of its proximate genus and differentia specifica are 

 distinct, and will enable us to understand distinctly the object to 

 be defined. In other words, we should assume that if by accident 

 we do not know the meaning of a given class name, we do know 

 the meaning of the next highest one, and can be made to under 

 stand the former by means of the latter. 1 



It is in fact an assumption of formal logic that people know the meaning 

 or connotation of the terms in common use, and of the concepts they form 

 about things ; and those logicians who confine their investigations to the 

 formal departments of the science, acting on this assumption, decline to deal 

 with definition at all. 2 Were the assumption in question always verified in 

 practice, definition would be &quot; obviously uncalled for and useless &quot;. 3 But the 

 assumption is not verified. &quot; Many persons are constantly diverging, and all 

 of us are occasionally diverging, from the common consensus of sound 

 opinion about the meaning of words. Accordingly, definitions are in practice 

 very often of extreme value &quot; ; 4 and this although we &quot; have no right to a 

 definition at all : the mere fact that [we] ask for one is in itself an admission of the 

 general truth of our postulate about language &quot; 5 [that we know the meaning 

 of the terms in common use]. 



51. FIXITY OF DEFINITION. Since definition is the analysis 

 and explicit statement of connotation, its fixity will depend 

 altogether on the fixity of the latter. It will have the same 

 conventional element and will be subject to the same acci 

 dental fluctuations and changes owing to progress of knowledge 

 or change in point of view (52). The fixing of the connotation 

 of our concepts and terms and the framing of our definitions have 

 a most important influence on advance in knowledge, and are 

 influenced in turn by the latter. 



Not only progress in knowledge may modify our definitions 

 by changing what we previously regarded as accidents we properties 

 into differentiae : a change in the point of view may effect a similar 

 modification and often does, especially in the mathematical 

 sciences, where Genetic Definitions (55) are of such frequent oc 

 currence. Thus an ellipse may be defined either as a &quot; conic 

 section right across the cone and not parallel to its base,&quot; or as 



1 &quot; If we are not to suppose that people know the meaning of the terms they 

 use, we will keep as near to this supposition as we can by assuming that they know 

 the meaning of every term except the one in question, and there is then all the re 

 quisite propriety and completeness in the offer of the genus and species by way of 

 definition.&quot; VENN, Empirical Logic, p. 302. 



2 Dr. ,Keynes, for example, deals only with Verbal, Formal and Real Propositions 

 in this connexion, not with Definition proper. 



8 VENN, op. cit., p. 280. 4 ibid. B ibidt 



