DEFINITION AND PROVINCE OF LOGIC. 



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 acces- 

 sible in the memory, but for so mar- 

 shalling the facts which we may at 

 •any time be engaged in investigat- 

 ing, 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, there- 

 fore, are operations specially instru- 

 mental 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 connexion 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 

 analysis, and pari passu with it, to 

 bring together or frame a set of rules 

 or canons for testing the sufficiency 

 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 

 separation of a complicated pheno- 

 menon into its component parts is not 



like a connected and interdependent 

 chain of proof. If one link of an 

 argument breaks, the whole drops to 

 the ground ; but one step towards an 

 analysis holds good and has an inde- 

 pendent 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 dis- 

 covered that all which we now call 

 simple substances are really com- 

 pounds. All other things are at any 

 rate compounded of those elements : 

 whether the elements themselves ad- 

 mit of decomposition, is an important 

 inquiry, but does not affect the cer- 

 tainty of the science up to that point. 

 I shall, accordingly, attempt to 

 analyse the process of inference, and 

 the processes subordinate to inference, 

 so far only as may be requisite for as- 

 certaining the difference between a 

 correct 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 we 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- 

 sary for effecting a cure. But we 

 should be justly liable to the criticism 

 involved in this objection, were we, 

 in a treatise on logic, to carry the 

 analysis of the reasoning process be- 

 yond the point at which any inac- 

 curacy which may have crept into it 

 must become visible. In learning 

 bodily exercises (to carry on the same 

 illustration) we do, and must, analyse 

 the bodily motions so far as is neces- 

 sary for distinguishing those which 

 ought to be performed from those 

 which ought not. To a similar extent, 

 and no further, it is necessary that 

 the logician should analyse the men- 

 tal processes with which logic is con- 

 cerned. Logic has no interest in 

 carrying the analysis beyond the point 

 at which it becomes apparent whether 



