ERROR AND FALLACIES 303 



The distinction between a &quot; formal &quot; fallacy and a &quot; material &quot; 

 fallacy is not fixed or clear any more than that between &quot; formal &quot; 

 and &quot;material&quot; logic. But at all events in a reasoning process, 

 we can distinguish between the narrower &quot; formal &quot; or &quot; consis 

 tency &quot; aspect, which is independent of the truth of the premisses 

 and the meaning of the terms used, and the &quot; material &quot; or 

 &quot;truth&quot; aspect. Now, the formal validity of an inference, in 

 this narrow sense, being independent of the subject-matter, i.e. 

 of the meaning of the concepts and terms employed, it is only 

 when the invalidity persists with the symbols, i.e. when some of 

 the formal laws of reasoning are violated, that the fallacy is a 

 formal one. If the fallacy lies in the language, i.e. in the meaning of 

 the terms employed, in ambiguities of meaning, then its source is 

 in the subject-matter, in the things for which the terms stand, and 

 the fallacy is a material fallacy. An ambiguous middle term in 

 a syllogism is, therefore, in this sense a material fallacy : when its 

 two distinct meanings are explicitly substituted for it by two dis 

 tinct terms, we have immediately the formal fallacy of quaternio 

 terminorum. In this meaning of the expression &quot; material 

 fallacy,&quot; all Aristotle s sophismata in dictione are, when they enter 

 into an inference, material fallacies ; while some of his fallacies 

 extra dictionem are formal in the sense that they can be repre 

 sented in symbols ; so that it is a mistake to confound Aristotle s 

 two lists with Whately s semi-logical and material fallacies, 

 respectively : a mistake into which Jevons seems to have fallen. 1 



(e) There is, finally, Professor Welton s classification, which we 

 purpose to follow : the classification according to the logical prin 

 ciples violated. 



273. FALLACIES INCIDENT TO CONCEPTION. We shall first 

 consider the fallacies incident to conception (Part I.) to the pro 

 cesses of forming concepts, of expressing these in terms, of secur 

 ing clearness and distinctness in thought and language by 

 definition and division, by analysis and comparison of the various 

 logical characteristics of concept and term. Violations of the 

 rules of logical definition and division lead to faulty conceptions, 

 and thence to erroneous judgments and reasonings. Indeed, most 

 of the fallacies incident to conception may be regarded as due 

 to faulty definition. They include many of Aristotle s sophis 

 mata in dictione. 



(a) EQUIVOCATION. The use of the same word in different 



1 Elementary Lessons in Logic, xx. and xxi. 



