IS INTRODUCTION. 



far as it goes is correct, and if it goes far enough for the 

 practical purposes of logic considered as an art. The separa- 

 tion 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 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 

 compounds. All other things are at any rate compounded of 

 those elements : whether the elements themselves admit of 

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

 certainty 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 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 muscles were 

 vitiated by local weakness, or other physical defect, a know- 

 ledge of their anatomy might be very necessary 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 beyond the point at which 

 any inaccuracy 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 necessary 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 mental processes with which Logic is concerned. Logic 

 has no interest in carrying the analysis beyond the point at 

 which it becomes apparent whether the operations have in any 

 individual case been rightly or wrongly performed : in the 

 .same manner as the science of music teaches us to discriminate 



