BOOK V. 



ON FALLACIES 



" Errare non modo affirmando et negaudo, sed etiam sentiendo, et in tacitA homi- 

 num cogitatione contingit." — Hobbes, Com-putaiio iivt Logica, ch. v. 



" II leur semble qu'il n'y a qu'a douter par fantaisie, et qu'il n'y a qii'a dire en 

 general que notre nature est infirnie ; que notre esprit est plein d'aveuglement ; qu'il 

 faut avoir un grand soin de se defairc de ses prejuges, et autres choses semblables. lis 

 pensent que cela suffit pour ne plus se laisser s^duire a ses sens, et pour iie plus se 

 t romper du tout. 11 ne suffit pas de dire que I'esprit est foible, il faut lui faire sentir 

 ses foiblesses. Ce n'est pas assez de dire qu'il est sujet h I'erreur, il faut lui d^couvrir 

 «n quoi consistent ses erreurs." — Malebkanche, Recherche de la Verite. 



CHAPTER I. 



ON FALLACIES IN GENERAL. 



§ I. It is a maxim of the school- 

 men that " contrariorum eadem est 

 scientia : " we never really know what 

 a thing is unless we are also able to 

 give a sufficient account of its oppo- 

 site. Conformably to this maxim, 

 one considerable section, in most 

 treatises on Logic, is devoted to the 

 subject of Fallacies ; and the practice 

 is too well worthy of observance to 

 allow of our departing from it. The 

 philosophy of reasoning, to be com- 

 plete, 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 evi- 

 dence needful to prove any given con- 

 clusion 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 

 ^rror would not be embraced instead 



of truth. But the general consent of 

 mankind, founded on their experi- 

 ence, vouches for their being far in- 

 deed from even this negative kind of 

 perfection in the employment of their 

 reasoning powers. 



In the conduct of life — in the prac 

 tical business of mankind — wrong 

 inferences, incorrect interpretations 

 of experience, unless after much cul- 

 ture of the thinking faculty, are ab- 

 solutely inevitable ; and with most 

 people, after the highest degree of 

 culture they ever attain, such errone- 

 ous inferences, producing correspond- 

 ing errors in conduct, are lamentably 

 frequent. Even in the speculations 

 to which eminent intellects have 

 systematically devoted themselves, 

 and in reference to which the col- 

 lective mind of the scientific world 

 is always at hand to aid the efforts 

 and correct the aberrations of indivi- 

 duals, it is only from the more perfect 

 sciences, from those of which the sub- 

 ject-matter is the least complicated, 

 that opinions not resting on a correct 

 induction have at length, generally 

 speaking, been expelled. In the de- 

 partments of inquiry relating to the 



