DEFINITION. 99 



of natural groups in the animal, vegetable, and mineral king 

 doms,&quot; 1 where the classes &quot; are not separated from each other by 

 rigid and definite lines &quot; 2 but &quot; shade off into each other by im 

 perceptible differences&quot;. 3 



&quot; Men form classes out of vaguely recognized resemblances long before 

 they are able to give an intensive definition of the class name, and in such 

 a case, if they are asked to explain their use of the name, their reply will be 

 to enumerate typical examples of the class. This would no doubt ordinarily 

 be done in an unscientific manner, but it would be possible to work it out 

 scientifically. The extensive definition of a name will take the form : X is 

 the name of the class of which Q^ Q^ . . . Q n are typical. This primitive 

 form of definition may also be called definition by type.&quot; 4 



These remarks call for a few observations. Firstly, in thus classifying by 

 type we are not classifying things at random, but are guided by their resemblance 

 to some central, typical example : the type becomes an ideal to which every 

 object must conform in a certain degree, that is to say, by the possession of a 

 certain group of attributes, before we admit it into the class ; so that even 

 in this process intension, and not extension, is the fundamental guiding 

 factor. 5 Secondly, although definition by type may be only &quot; a rough and 

 ready means of making others recognize the objects of which we are speak 

 ing,&quot; 6 and although it does not give us any knowledge of their nature or 

 essence (50), as ordinary (or intensive) definition does, 7 yet it contributes not 

 a little to securing clearness in our ideas (49) and to removing ambiguity in 

 language by safeguarding identity of reference in our terms. Thirdly, if 

 we choose from any given class of things, say metals, a smaller group com 

 posed of members so numerous and so different from one another such as 

 aluminium, antimony, copper, gold, iron, mercury, sodium, zinc that they 

 possess in common those attributes and those only which are common to all 

 metals (thus forming the known comprehension of the term metal], our smaller 

 group will form a perfect typical definition of the larger group. Such a typical 

 collection, thus chosen from the denotation, is called the exemplification of 

 the class name. 8 



We remarked above (50) that the ordinary definition per genus et differ- 

 entiam will explain a thing only to one who already understands the genus 

 and the differentia of the latter : so, too, extensive definition would be useless 

 to one who had no previous acquaintance with the typical members chosen 

 to exemplify the class in question. 



54. &quot; NOMINAL&quot; AND &quot;REAL&quot; DEFINITIONS ; VERBAL DIS 

 PUTES. We have stated (49, 50) that all definition is at once 



1 KEYNES, op. cit. t p. 34. 2 WELTON, op. cit., p. 144. 



3 ibid., p. 113, quoted from Professor CAIRNES, Logical Method of Political 

 Economy, pp. 139-141, Cf. supra, 51. 



4 KEYNES, op. cit., p. 34. 6 ibid., footnote. Cf. WELTON, op. cit., p. 144. 



6 WELTON, op. cit., p. 122. 



7 Dr. VENN says (op. cit., p. 306) that &quot; from the logical point of view it is less 

 of a true definition than is the so-called description &quot;. Cf. ibid., p. 279. 



8 KEYNES, op. cit., p. 33, 



7* 



