328 THE SCIENCE OF LOGIC 



reductio ad impossibile, or indirect proof (169, 254, &amp;lt;). In this pro 

 cess we disprove a thesis by showing that the assumption of its 

 truth would lead to absurdities ; or we prove a thesis by showing 

 that the assumption of its falsity would lead to absurdities. Now, 

 the fallacy under consideration is committed if the absurdities do 

 in reality follow not from the assumption made, but from some 

 extraneous and irrelevant proposition which we have foisted into 

 our argument. The absurd conclusion is wrdngly sought to be 

 fathered upon the initial assumption. Hence Aristotle calls the 

 fallacy also &quot; Non per hoc&quot; &quot; Non propter hoc&quot; which is the 

 answer by which the fallacy ought to be met : &quot; Your conclusion 

 is indeed absurd (or impossible), not, however, because of your 

 assumption about my thesis, but quite independently of it &quot;. 

 The following instance is from Father Joyce s Logic (p. 281): 

 &quot; Thus, if we suppose the sophist s opponent to have affirmed that 

 the death penalty for murder is just, the sophist might argue as 

 follows : The position leads to an absurdity : for granting that 

 the death penalty for murder is just, and that punishment is to 

 be held just in so far as it is efficacious as a deterrent, then it 

 follows that it would be equally just to inflict the death-penalty 

 for pocket-picking . Here the original statement has nothing 

 to do with the conclusion obtained. This follows from the 

 principle that the justice of a punishment is measured by its 

 efficacy as a deterrent, a principle which is in no way connected 

 with the statement that the death penalty for murder is just.&quot; 



Aristotle includes under the head of this fallacy all cases in 

 which a conclusion is drawn from premisses which are quite 

 irrelevant to it, and which, for want of any better classification 

 we describe as cases of &quot; No n Sequitur &quot; : &quot; arguments so foolish 

 and inconsequent, that they cannot even be said to simulate 

 cogency; these cannot be positively characterized, but must be 

 lumped together by the mere negative mark of inconclu- 



siveness 



As the fallacy of non causa pro causa, in Aristotle s sense, 

 was peculiar to dialectical disputations, and is of comparatively 

 rare occurrence nowadays, its name has been transferred pretty 

 commonly to the inductive fallacy of mistaking for the cause of an 

 event something that is not really the cause, the fallacy of Post 

 (or cum} hoc, ergo propter hoc (infra, B. c}. This mistake, of con 

 founding temporal sequence or coexistence of facts with causality, 

 1 JOSEPH, op. cit., p. 529. 



