PREFACE TO THE THIRD AND FOURTH EDITIONS. 



Several criticisms, of a more or less controversial charactei', on this 

 work, have appeared since the publication of the second edition ; and Dr. 

 Whewell has lately published a reply to those parts of it in which some of 

 his opinions were conti'overted.* 



I have carefully reconsidered all the points on which my conclusions 

 have been assailed. But I have not to announce a change of opinion on 

 any matter of importance. Such minor oversights as have been detected, 

 cither by myself or by my critics, I have, in general silently, corrected : but 

 it is not to be inferred that I agree with the objections which have been 

 made to a passage, in every instance in which I have altered or canceled it. 

 I have often done so, merely that it might not remain a stumbling-block, 

 when the amount of discussion necessary to place the matter in its true 

 light would have exceeded what was suitable to the occasion. 



To several of the arguments which have been urged against me, I have 

 thought it useful to reply with some degree of minuteness ; not from any 

 taste for controversy, but because the opportunity was favorable for pla- 

 cing my own conclusions, and the grounds of them, more clearly and com- 

 pletely before the reader. Truth on these subjects is militant, and can 

 only establish itself by means of conflict. The most opposite opinions can 

 make a plausible show of evidence while each has the statement of its own 

 case ; and it is only possible to ascertain which of them is in the right, af- 

 ter hearing and comparing what each can say against the other, and what 

 the other can urge in its defense. 



Even the criticisms from which I most dissent have been of great serv- 

 ice to me, by showing in what places the exposition most needed to be 

 impi'oved, or the argument strengthened. And I should have been well 

 pleased if the book had undergone a much greater amount of attack ; as in 

 that case I should probably have been enabled to improve it still more than 

 I believe I have now done. 



In the subsequent editions, the attempt to improve the work by addi- 

 tions and corrections, suggested by criticism or by thought, has been con- 

 * Now forming a chapter in his volume on " The Philosophy of Discovery." 



