to6 THE SCIENCE OF LOGIC. 



may be called nominal definition ; e.g. &quot; Political Autonomy is 

 Home Rule&quot; , &quot; The Irish word Gort means a tillage-field&quot;. 

 The explanations of terms &quot; peculiar to certain classes, the slang 

 of thieves, schoolboys and sporting persons, and the whole 

 vocabulary of peculiar expressions required by sailors, miners, 

 and indeed most classes of workmen,&quot; 1 belong to this class of 

 definitions. In this as in the former classes there is scarcely any 

 reference to things present to the speaker s mind ; his chief concern 

 is with words. 



Thirdly, what is called Private, or Special, or Conventional, or 

 Technical Definition, is mainly nominal in its character. It con 

 sists in a person s assigning to some term a perfectly definite 

 sense in which he is about to use the term in a given context 

 in a discussion, essay, treatise, etc. The meaning assigned may 

 be different, and is usually partly different, from the commonly 

 accepted meaning ; or, rather, as a rule, it is the vagueness and 

 ambiguity of the latter that creates the need for the former. 2 

 The sole aim in thus assigning a definite meaning to terms at the 

 outset of any reasoning process is to secure identity of reference 

 and avoid ambiguity. This was what the Scholastics intended 

 by the maxim &quot; Initium disputandi, definitio nominis &quot;. All 

 science abounds in terms having definite meanings attached to 

 them, usually somewhat different, often entirely different, from 

 the meaning attached to them in ordinary usage. We may 

 instance the words Substance, Accident, Form, Extension, in phil 

 osophy. 



56. SOME SUBSTITUTES FOR DEFINITION. It has been 

 already observed that it is not always possible to give a strict 

 definition per genus et differentiam, that the application of a term 

 is often determined by some such process as exemplification, or by 

 a direct appeal to experience. Sometimes, too, a clear and dis 

 tinct idea of the object is conveyed by the &quot; exercise of the 

 imagination&quot;. 3 This is frequently resorted to in the mathe 

 matical sciences. A description of the process by which we may 

 imagine an object to be produced is called a Genetic or Constructive 

 Definition. For example, &quot;A circle is a curve generated by one 



1 VENN, op. cit., p. 282. 



a Hence legal definitions, i.e. those embodied in Acts of Parliament and 

 judicial decisions, are commonly regarded as nominal. Cf. JOSEPH, Logic, pp. 188, 

 189. 



a VENN, op. cit., p. 279. 



