BOOK V. 



ON FALLACIES. 



' 11 leur semble qu'il n'y a qu'ii douter par fantaisie, et qu'ii n'y a qu'^ dire en gen6ral 

 que notre nature est infirme ; que notre esprit est plain d'aveuglement ; qu'il faut avoir un 

 grand soin de se defaire de ses prejuges, et autres choses semblables. lis pensent que cela 

 suffit pour ne plus se laisser seduire a ses sens, et pour ne plus se tromper du tout. 11 ne 

 sufiit 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 a I'erreur, il faut lui decouvrir en quoi consistent ses erreurs." 

 — Malebranche, Recherche de la Verite. 



" Errare non modo afErmando et negando, sed etiam sentiendo, et in tacita hominum 

 cogitatione contingit." — Hobbes, Computatio sive Legica, eh. v. 



CHAPTER I. 



OF FALLACIES IN GENERAL. 



§ 1. It is a maxim of tlie schoolmen, that " contrarioinim eadem est 

 scientia :" we never really know what a tiling is, unless we are also 

 able 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 Fallacies; and the practice is too well worthy of 

 observance, to allow of our departing from it. The jjhilosophy of rea- 

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

 of good reasoning. 



We have endeavored to ascertain the principles by which the suffi- 

 ciency 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 indi- 

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

 But the general consentof mankind, founded upon all 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 ordinary business of mankind — UTong 

 inferences, incorrect interpretations of experience, unless after much 

 culture of the thinking faculty, are absolutely ine^-itable : and with 

 most people after the highest degree of culture they ever attain (unless 

 where the events of their daily life supply an immediate con-ective), 

 such erroneous inferences are as fi-equent if not more frequent than 

 coiTect inferences, correct intei-pretations of experience. Even in the 

 speculations to which the highest intellects systematically devote them- 

 selves, and in reference to Avhich the collective mind of the scientific 

 world is always at hand to aid the efforts and control the aberrations 



