22 INTRODUCTION. 



accompany a violent death. This he must learn from his own experience 

 and observation, or from that of others, his predecessors in his peculiar 

 pursuit. But logic sits in judgment on the sufficiency of that observation 

 and experience to justify his rules, and on the sufficiency of his I'ules 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. It does not teach 

 that any particular fact proves any other, but points out to what conditions 

 all facts must conform, in order that they may prove other facts. To de- 

 cide whether any given fact fulfills these conditions, or whether facts can 

 be found which fulfill them in a given case, belongs exclusively to the par- 

 ticular 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, ars artium; the science of science itself. All 

 science consists of data and conclusions from those data, of proofs and what 

 they prove : now logic points out what relations must subsist between data 

 and whatever can be concluded from them, between proof and every thing 

 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 con- 

 form to those relations, under the penalty of making false inferences — of 

 drawing conclusions which are not grounded in the realities of things. 

 Whatever has at any time been concluded justly, whatever knowledge has 

 been acquired otherwise than by immediate intuition, depended on tlie ob- 

 servance 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 further for a solution of the ques- 

 tion, 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 instance 

 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 unacquainted with them. 



A science may undoubtedly be brought to a certain, not inconsiderable, 

 stage of advancement, without the application of any other logic to it than 

 what all persons, who are said to have a sound understanding, acquire em- 

 pirically 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 before 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 extraordinary genius, or by the 

 accidental acquisition of a good set of intellectual habits, may work with- 

 out principles 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 mankind 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 precur- 

 sor, or as its accompaniment and necessary condition, a corresponding im- 

 provement in the notions and principles of logic received among the most 

 advanced thinkers. And if several of the more difficult sciences are still 



