Book V.
On Fallacies.
“Errare non modo affirmando et negando, sed etiam sentiendo, et in tacitâ hominum cogitatione contingit.”—Hobbes, Computatio sive Logica, chap. v.
“Il leur semble qu’il n’y a qu’à douter par fantaisie, et qu’il n’y a qu’à dire en général que notre nature est infirme; que notre esprit est plein d’aveuglement: qu’il faut avoir un grand soin de se défaire de ses préjugés, et autres choses semblables. Ils pensent que cela suffit pour ne plus se laisser séduire à ses sens, et pour ne plus se tromper du tout. Il ne suffit pas de dire que l’esprit est foible, il faut lui faire sentir ses foiblesses. Ce n’est pas assez de dire qu’il est sujet à l’erreur, il faut lui découvrir en quoi consistent ses erreurs.”—Malebranche, Recherche de la Vérité.
Chapter I.
Of Fallacies In General.
§ 1. 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 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 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.