160 NAMES AND PROPOSITIONS. 



" There are, therefore, expressions, commonly passing for 

 definitions, which include in themselves more than the mere 

 explanation of the meaning of a term. But it is not correct 

 to call an expression of this sort a peculiar kind of definition. 

 Its difference from the other kind consists in this, that it is 

 not a definition, but a definition and something more. The 

 definition above given of a triangle, obviously comprises not 

 one, but two propositions, perfectly distinguishable. The one 

 is, ' There may exist a figure, bounded by three straight lines ;' 

 the other, ' And this figure may be termed a triangle.' The 

 former of these propositions is not a definition at all : the 

 latter is a mere nominal definition, or explanation of the use 

 and application of a term. The first is susceptible of truth or 

 falsehood, and may therefore be made the foundation of a 

 train of reasoning. The latter can neither be true nor false ; 

 the only character it is susceptible of is that of conformity or 

 disconformity to the ordinary usage of language." 



There is a real distinction, then, between definitions of 

 names, and what are erroneously called definitions of things ; 

 but it is, that the latter, along with the meaning of a name, 

 covertly asserts a matter of fact. This covert assertion is not 

 a definition, but a postulate. The definition is a mere iden- 

 tical proposition, which gives information only about the use 

 of language, and from which no conclusions affecting matters 

 of fact can possibly be drawn. The accompanying postulate, 

 on the other hand, affirms a fact, which may lead to conse- 

 quences of every degree of importance. It affirms the actual 

 or possible existence of Things possessing the combination of 

 attributes set forth in the definition ; and this, if true, may be 

 foundation sufficient on which to build a whole fabric of 

 scientific truth. 



We have already made, and shall often have to repeat, the 

 remark, that the philosophers who overthrew Realism by no 

 means got rid of the consequences of Realism, but retained 

 long afterwards, in their own philosophy, numerous proposi- 

 tions which could only have a rational meaning as part of a 

 Realistic system. It had been handed down from Aristotle, 

 and probably from earlier times, as an obvious truth, that the 



