FALLACIES OF RATIOCINATION. 433 



though .committed, like many other fallacies, oftener 

 in the silence of thought than in express words, for 

 it can scarcely be clearly enunciated without being 

 detected. And so with another form of fallacy, not 

 substantially different from the preceding ; the erro- 

 neous conversion of an hypothetical proposition. The 

 proper converse of an hypothetical proposition is 

 this : If the consequent be false the antecedent is false ; 

 but this, If the consequent be true, the antecedent is 

 true, by no means holds good, but is an error corre- 

 sponding to the simple conversion of an universal 

 affirmative. Yet hardly anything is more common 

 than for people, in their private thoughts, to draw 

 this inference. As when the conclusion is accepted, 

 which it so often is, for proof of the premisses. That 

 the premisses cannot be true if the conclusion is false, is 

 the unexceptionable foundation of the legitimate mode 

 of reasoning called a reductio ad absurdum. But men 

 continually think and express themselves as if they 

 also believed that the premisses cannot be false if the 

 conclusion is true. The truth, or supposed truth, of 

 the inferences which follow from a doctrine, often 

 enables it to find acceptance in spite of gross ab- 

 surdities in it. How many systems of philosophy, 

 which had scarcely any intrinsic recommendation, 

 have been received by thoughtful men because they 

 were supposed to lend additional support to religion, 

 morality, some favourite view of politics, or some 

 other cherished persuasion ? not merely because their 

 wishes were thereby enlisted on its side, but because 

 its leading to what they deemed sound conclusions 

 appeared to them a strong presumption in favour of 

 its truth : though the presumption, when viewed in 

 its true light, amounted only to the absence of that 

 particular kind of evidence of falsehood, which would 



VOL. II. 2 F 



