PREFACE TO THE THIRD EDITION. 



IN the preface to the second edition, I have de 

 scribed myself as resisting the temptation to amplify, 

 which the occasion raised. Reasons have since arisen 

 for yielding to the desire which I then felt to acid 

 justifications of the scheme set forth. 



The immediate cause for this change of resolve, has 

 been the publication of several objections by Prof. 

 Bain in his Logic. Permanently embodied, as these 

 objections are, in a work intended for the use of 

 students, they demand more attention than such as 

 have been made in the course of ordinary criticism; 

 since, if they remain unanswered, their prejudicial 

 effects will be more continuous. 



While to dispose of these I seize the opportunity 

 afforded by a break in my ordinary work, I have 

 thought it well at the same time to strengthen my 

 own argument, by a re-statement from a changed 

 point of view. 



Feb., 1871. 



