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CHAPTER VI. 

 FALLACIES OF RATIOCINATION. 



1 . WE have now, in our progress through the 

 classes of Fallacies, arrived at those to which, in the 

 common books of logic, the appellation is in general 

 exclusively appropriated ; those which have their seat 

 in the ratiocinative or deductive part of the investiga- 

 tion of truth. On these fallacies it is the less neces- 

 sary for us to insist at any length, as they have been 

 so admirably treated in a work familiar to almost all, 

 in this country at least, who feel any interest in tbese 

 speculations, Archbishop Whately's Logic. Against 

 the more obvious forms of this class of fallacies, the 

 rules of the syllogism are a complete protection. Not 

 (as we have so often said) that the ratiocination cannot 

 be good unless it be in the form of a syllogism ; but 

 that, by showing it in that form, we are sure to discover 

 if it be bad, or at least if it contain any fallacy of this 

 class. 



2. Among Fallacies of Ratiocination we ought, 

 perhaps, to include the errors committed in processes 

 which have the appearance only, not the reality, of an 

 inference from premisses; the fallacies connected with 

 the conversion and sequipollency of propositions. I 

 believe errors of this description to be far more fre- 

 quently committed than is generally supposed, or than 

 their extreme obviousness might seem to admit of. 

 For example, the simple conversion of an universal 

 affirmative proposition, All A are B therefore all B 

 are A, I take to be a very common form of error-. 



