DEFINITION AND PROVINCE OF LOGIC. 1 1 



The distinction is, that the science or knowledge 

 of the particular subject-matter furnishes the evidence, 

 while logic furnishes the principles and rules of the 

 estimation of evidence. Logic does not pretend to 

 teach the surgeon what are the symptoms which indi- 

 cate a violent death. This he must learn from his 

 own experience and observation, or from that of others, 

 his predecessors in his peculiar science. But logic 

 sits in judgment on the sufficiency of that observation 

 and experience to justify his rules, and on the suffici- 

 ency of his rules to justify his conduct. It does not 

 give him proofs, but teaches him what makes them 

 proofs, and how he is to judge of them. Logic alone 

 can never show that the fact A proves the fact B ; but 

 it can point out to what conditions all facts must 

 conform, in order that they may prove other facts. 

 To decide whether any given fact fulfils these condi- 

 tions, or whether facts can be found which fulfil them 

 in any given case, belongs, exclusively, to the parti- 

 cular art or science, or to our knowledge of the par- 

 ticular subject. 



It is in this sense that logic is, what Bacon so 

 expressively called it, ars artium ; the science of 

 science itself. All science consists of data and con- 

 clusions from those data, of proofs and what they 

 prove: now logic points out what relations must sub- 

 sist between data and whatever can be concluded 

 from them, between proof and everything which it 

 can prove. If there be any such indispensable rela- 

 tions, and if these can be precisely determined, every 

 particular branch of science, as well as every indi- 

 vidual in the guidance of his conduct, is bound 

 to conform to those relations, under the penalty of 

 making false inferences, of drawing conclusions which 

 are not grounded in the realities of things. Whatever 



