14 INTRODUCTION. 



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 founda- 

 tion 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, 

 J 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 

 phenomenon 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 independent value, though we should 

 never be able to make a second. The results of 

 analytical chemistry are not the less valuable, though 

 it should be discovered that all which we now call 

 simple substances are really compounds. All other 

 things are at any rate compounded of those elements: 

 whether the elements themselves admit of decomposi- 

 tion, is an important inquiry, but does not affect the 

 certainty of the science up to that point. 



I shall, accordingly, attempt to analyze the process 

 of inference, and the processes subordinate to infe- 

 rence, so far only as may be requisite for ascertaining 

 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 



