FUNCTIONS AND VALUE OF THE SYLLOGISM. 265 



bestow greater attention upon the process, and to 

 weigh more carefully the sufficiency of the experience 

 appealed to, for supporting the inference grounded 

 upon it. There is another, and a more important, 

 advantage. In reasoning from a course of individual 

 observations to some new and unobserved case, which 

 we are but imperfectly acquainted with (or we should 

 not be inquiring into it), and in which, since we are 

 inquiring into it, we probably feel a peculiar interest ; 

 there is very little to prevent us from giving way to 

 negligence, or to any bias which may affect our wishes 

 or our imagination, and, under that influence, accept- 

 ing insufficient evidence as sufficient. But if, instead 

 of concluding straight to the particular case, we place 

 before ourselves an entire class of facts, the whole 

 contents of a general proposition, every tittle of 

 which is legitimately inferrible from our premisses, if 

 that one particular conclusion is so ; there is then a 

 considerable likelihood that if the premisses are insuf- 

 ficient, and the. general inference, therefore, ground- 

 less, it will comprise within it some fact or facts the 

 reverse of which we already know to be true ; and we 

 shall thus discover the error in our generalisation, by 

 what the schoolmen termed a reductio ad impossibile. 



Thus if, during the reign of Marcus Aurelius, a 

 subject of the Roman empire, under the bias natu- 

 rally given to the imagination and expectations by 

 the lives and characters of the Antonines, had been 

 disposed to conclude that Commodus would be a just 

 ruler; supposing him to stop there, he might only 

 have been undeceived by sad experience. But if he 

 reflected that this conclusion could not be justifiable 

 unless from the same evidence he was also warranted 

 in concluding some general proposition, as, for 

 instance, that all Roman emperors are just rulers ; he 



