BOOK V. 



ON FALLACIES. 



"Errare non modo affinmando et negando, sed etiam sentiendo, et in tacita liominum cogi- 

 tatione contingit." — Hobbes, Computatio sive Logica, chap. v. 



" II leur semble qu'il n'y a qu'k douter par fantaisie, et qiril n'y a qu'a dire en ge'neral que 

 notre nature est infirme ; que notre esprit est plein d'aveugiement : qu'il faut avoir un grand 

 soin de se de'faire de ses prejuge's, et autres choses semblables. lis pensent que cela suflSt 

 pour ne plus se laisser seduire a ses sens, et pour ne plus se tromper 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 a I'ei-reur, il faut lui de'couvrir en quoi consistent ses erreurs." — Malebkanche, 

 Recherche de la V€rit€. 



CHAPTER I. 



OF FALLACIES IN GENERAL. 



§ 1. It is a maxim of the school-men, that " contvaviovum eadem est sci- 

 entia :" we never really know what a thing 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 philosophy of reasoning, 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 sufficiency 

 of any proof can be tested, and by which the nature and amount of evi- 

 dence 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 man- 

 kind, 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 infer- 

 ences, incorrect interpretations of experience, unless after much culture of the 

 thinking faculty, are absolutely inevitable ; and with most people, after the 

 highest degree of culture they ever attain, such erroneous inferences, produ- 

 cing corresponding errors in conduct, are lamentably frequent. Even in the 

 speculations to which eminent intellects have systematically devoted them- 

 selves, and in reference to which the collective mind of the scientific world is 

 always at hand to aid the efforts and correct the aberrations of individuals, 

 it is only from the more perfect sciences, from those of which the subject- 

 matter is the least complicated, that opinions not resting on a correct in- 

 duction have at length, generally speaking, been expelled. In the depart- 



