INTtlODtJCTION; 



any other, but points out to what 

 conditions all facts must conform, in 

 order that they may prove other facts. 

 To decide whether any given fact 

 fulfils these conditions, or whether 

 facts can be found which fulfil them 

 in a given case, belongs exclusively to 

 the particular art or science, or to our 

 knowledge of the particular subject. 



It is in this sense that logic is, what 

 it was so expressively called by the 

 schoolmen and by Bacon, ai's art mm ; 

 the science of science itself. All 

 science consists of data and conclu- 

 sions from those data, of proofs and 

 what they prove : now logic points 

 out what relations must subsist be- 

 tween data and whatever can be 

 concluded from them, between proof 

 and everything which it can prove. 

 If there be any such indispensable 

 relations, and if these can be precisely 

 determined, every particular branch 

 of science, as well as every individual 

 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 reali- 

 ties of things. Whatever has at any 

 time been concluded justly, whatever 

 knowledge has been acquired other- 

 wise than by immediate intuition, 

 depended on the observance of the 

 laws which it is the province of logic 

 to investigate. If the conclusions are 

 just, and the knowledge real, those 

 laws, whether known or not, have 

 been observed. 



' § 6. We need not, therefore, seek 

 any farther for a solution of the 

 question, so often agitated, respecting 

 the utility of logic. If a science of 

 logic exists, or is capable of existing, 

 it must be useful. If there be rules 

 to which every mind consciously or 

 ■Unconsciously conforms in every in- 

 stance in which it infers rightly, there 

 seems little necessity for discussing 

 whether a person is more likely to 

 observe those rules, when he knows 

 the rules, than when he is unac- 

 c^uainted with them. 



A science inay undoulotedly bd 

 brought to a certain, not inconsider- 

 able, stage of advancement, without 

 the application of any other logic to 

 it than what all persons, who are 

 said to have a sound xinderstanding, 

 acquire empirically in the course of 

 their studies. Mankind judged of 

 evidence, and often correctly, before 

 logic was a science, or they never 

 could have made it one. And they 

 executed great mechanical works be- 

 fore they understood the laws of 

 mechanics. But there are limits both, 

 to what mechanicians can do without; 

 principles of mechanics, and to what 

 thinkers can do without principles of 

 logic. A few individuals, by extra- 

 ordinary genius, or by the accidental 

 acquisition of a good set of intellec- 

 tual habits, may work without prin- 

 ciples in the same way, or nearly the 

 same way, in which they would have 

 worked if they had been in possession 

 of principles. But the bulk of man- 

 kind require either to understand the 

 theory of what they are doing, or to 

 have rules laid down for them by 

 those who have understood the theory. 

 In the progress of science from its 

 easiest to its more difficult problems, 

 each great step in advance has usually 

 had either as its precursor, or as its 

 accompaniment and necessary condi- 

 tion, a corresponding improvement in 

 the notions and principles of logic 

 received among the most advanced 

 thinkers. And if several of the more 

 difficult sciences are still in so defec- 

 tive a state ; if not only so little is 

 proved, but disputation has not ter- 

 minated even about the little which 

 seemed to be so ; the reason perhaps 

 is, that men's logical notions have not 

 yet acquired the degree of extension, 

 or of accuracy, requisite for the esti- 

 mation of the evidence proper to those 

 particular departments of knowledge. 



§ 7. Logic, then, is the science of 

 the operations of the understanding 

 which are subservient to the estima- 

 tion of evidence : both the process 

 itself of advancing from known truths 



