DEFINITION AND PROVINCE OF LOGIC. 23 



in so defective a state ; if not only so little is proved, but disputation has 

 not terminated 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 estimation of the evidence prop- 

 er to those particular departments of knowledge. 



§ V. Logic, then, is the science of the operations of the understanding 

 which are subservient to the estimation of evidence: both the process it- 

 self of advancing from known truths to unknown, and all other intellectual 

 operations in so far as auxiliary to this. It includes, therefore, the opera- 

 tion of Naming ; for language is an instrument of thought, as well as a 

 means of communicating our thoughts. It includes, also. Definition, and 

 Classification. For, the use of these operations (putting all other minds 

 than one's own out of consideration) is to serve not only for keeping our 

 evidences and the conclusions from them permanent and readily accessible 

 in the memory, but for so marshaling the facts which Ave may at any time 

 be engaged in investigating, as to enable us to perceive more clearly what 

 evidence there is, and to judge with fewer chances of error whether it be 

 sufficient. These, therefore, are operations specially instrumental to the 

 estimation of evidence, and, as such, are within the province of Logic. 

 There are other more elementary processes, concerned in all thinking, such 

 as Conception, Memory, and the like ; but of these it is not necessary that 

 Logic should take any peculiar cognizance, since they have no special 

 connection with the problem of Evidence, further than that, like all other 

 problems addressed to the understanding, it presupposes them. 



Our object, then, will be, to attempt a correct analysis of the intellectual 

 process called Reasoning or Inference, and of such other mental operations 

 as are intended to facilitate this : as well as, on the foundation of this anal- 

 ysis, and pari passu with it, to bring together or frame a set of rules or 

 canons for testing the sufliciency of any given evidence to prove any given 

 proposition. 



With respect to the first part of this undertaking, I do not attempt to 

 decompose the mental operations in question into their ultimate elements. 

 It is enough if the analysis as far as it goes is correct, and if it goes far 

 enough for the practical purposes of logic considered as an art. The sep- 

 aration of a complicated phenomenon into its component parts is not like 

 a connected and interdependent chain of proof. If one link of an argu- 

 ment breaks, the whole drops to the ground ; but one step toward an anal- 

 ysis holds good and has an independent value, though we should never be 

 able to make a second. The results which have been obtained by analytical 

 chemistry are not the less valuable, though it should be discovered that 

 all which Ave now call simple substances are really compounds. All other 

 things are at any rate compounded of those elements: whether the ele- 

 ments themselves admit of decomposition, is an important inquiry, but 

 does not affect the certainty of the science up to that jjoint. 



I shall, accordingly, attempt to analyze the process of inference, and the 

 processes subordinate to inference, so far only as may be requisite for as- 

 certaining the difference betAveen a cori-ect and an incorrect performance 

 of those processes. The reason for thus limiting our design, is evident. 

 It has been said by objectors to logic, that Ave do not learn to use our 

 muscles by studying their anatomy. The fact is not quite fairly stated; 

 for if the action of any of our muscles were vitiated by local weakness, or 

 other physical defect, a knowledge of their anatomy might be very neces- 



