CHAPTER I. 



OF FALLACIES IN GENERAL. 



1. IT is a maxim of the schoolmen, that &quot; contra- 

 riorum eadem est scientia:&quot; we never really know what a thing 

 is, unless we are also ahle to give a sufficient account of its 

 opposite. Conformably to this maxim, one considerable section, 

 in most treatises on Logic, is devoted to the subject of Falla 

 cies ; and the practice is too well worthy of observance, to allow 

 of our departing from it. The philosophy of reasoning, to be 

 complete, ought to comprise the theory of bad as well as of 

 good reasoning. 



We have endeavoured to ascertain the principles by which 

 the sufficiency of any proof can be tested, and by which the 

 nature and amount of evidence needful to prove any given 

 conclusion can be determined beforehand. If these principles 

 were adhered to, then although the number and value of the 

 truths ascertained would be limited by the opportunities, or 

 by the industry, ingenuity, and patience, of the individual 

 inquirer, at least error would not be embraced instead of truth. 

 But the general consent of mankind, founded on their 

 experience, vouches for their being far indeed from even this 

 negative kind of perfection in the employment of their 

 reasoning powers. 



In the conduct of life in the practical business of mankind 

 wrong inferences, incorrect interpretations of experience, 

 unless after much culture of the thinking faculty, are abso 

 lutely inevitable : and with most people, after the highest 

 degree of culture they ever attain, such erroneous inferences, 

 producing corresponding errors in conduct, are lamentably 

 frequent. Even in the speculations to which eminent intel 

 lects have systematically devoted themselves, and in reference 

 to which the collective mind of the scientific world is always 



