10 INTRODUCTION. 



Evidence. So far forth as belief professes to be 

 founded upon proof, the office of logic is to supply a 

 test for ascertaining whether or not the belief is well 

 grounded. With the claims which any proposition 

 has to belief on its own intrinsic evidence, that is, 

 without evidence in the proper sense of the word, logic 

 has nothing to do. 



5. As the far greatest portion of our knowledge, 

 whether of general truths or of particular facts, is 

 avowedly matter of inference, nearly the whole, not 

 only of science, but of human conduct, is amenable 

 to the authority of logic. To draw inferences has 

 been said to be the great business of life. Every one 

 has daily, hourly, and momentary need of ascertaining 

 facts which he has not directly observed ; not from 

 any general purpose of adding to his stock of know- 

 ledge, but because the facts themselves are of import- 

 ance to his interests or to his occupations. The 

 business of the magistrate, of the military commander, 

 of the navigator, of the physician, of the agriculturist, 

 is merely to judge of evidence, and to act accordingly. 

 They all have to ascertain certain facts, in order that 

 they may afterwards apply certain rules, either devised 

 by themselves, or prescribed for their guidance by 

 others ; and as they do this well or ill, so they dis- 

 charge well or ill the duties of their several callings. 

 It is the only occupation in which the mind never 

 ceases to be engaged ; and is the subject, not of logic, 

 but of knowledge in general. Our definition of logic, 

 therefore, will be in danger of including the whole 

 field of knowledge, unless we qualify it by some further 

 limitation, showing distinctly where the domain of the 

 other arts and sciences and of common prudence ends, 

 and that of logic begins. 



