iv PREFACE. 



tinctions which were contained in the old Logic have been gradually omit- 

 ted from the writings of its later teachers ; and it appeared desirable both 

 to revive these, and to reform and rationalize the philosophical foundation 

 on which they stood. The earlier chapters of this preliminary Book will 

 consequently appear, to some readers, needlessly elementary and scholastic. 

 But those who know in what darkness the nature of our knowledge, and 

 of the pi'ocesses by which it is obtained, is often involved by a confused 

 apprehension of the import of the different classes of Words and Asser- 

 tions, will not regard these discussions as either frivolous, or irrelevant to 

 the topics considered in the later Books. 



On the subject of Induction, the task to be performed was that of gener- 

 alizing the modes of investigating truth and estimating evidence, by which 

 so many important and recondite laws of nature have, in the various sci- 

 ences, been aggregated to the stock of human knowledge. That this is not 

 a task free from difficulty may be presumed from the fact that even at a 

 very recent period, eminent writers (among whom it is sufficient to name 

 Archbishop Whately, and the author of a celebrated article on Bacon in the 

 JEdinburgh llevieio) have not scrupled to pronounce it impossible.* The 

 author has endeavored to combat their theory in the manner in which Di- 

 ogenes confuted the skeptical reasonings against the possibility of motion ; 

 remembering that Diogenes's argument would have been equally conclu- 

 sive, though his individual perambulations might not have extended be- 

 yond the circuit of his own tub. 



Whatever may be the value of what the author has succeeded in effect- 

 ing on this branch of his subject, it is a duty to acknowledge that for much 

 of it he has been indebted to several important treatises, partly historical 

 and partly philosophical, on the generalities and processes of physical sci- 

 ence, which have been published within the last few years. To these ti'ea- 

 tises, and to their authors, he has endeavored to do justice in the body of 

 the work. But as with one of these writers. Dr. Whewell, he has occasion 

 frequently to express differences of opinion, it is more particularly incum- 

 bent on him in this place to declare, that without the aid derived from the 



* In the later editions of Archbishop Whately's "Logic," he states his meaning to be, not 

 that "rules" for the ascertainment of truths by inductive investigation can not be laid down, 

 or that they may not be "of eminent service," but that they "must always be comparatively 

 vague and general, and incapable of being built up into a regular demonstrative theory like 

 that of the Syllogism." (Book iv., ch. iv., § 3.) And he observes, that to devise a system 

 for this purpose, capable of being "brought into a scientific form," would be an achievement 

 which "he must be more sanguine than scientific who expects." (Book iv., ch. ii., § 4.) To 

 effect this, however, being the express object of the portion of the present work which treats 

 of In4uction, the words in the text are no overstatement of the difference of opinion between 

 Archbishop Whately and me on the subject. 



