iv PREFACE. 



cUiating the principles of the art with as much as is well grounded 

 in the doctrines and objections of its assailants. 



The same abstinence from details could not be observed in the 

 First Book, on Names and Propositions, because many useful prin- 

 ciples and distinctions which were contained in the old Logic have 

 been gradually omitted from the writings of its later teachers ; and 

 it appeared desirable both to revive these, and to reform and rationa 

 lise 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 knoAV 

 in what darkness the nature of our knowledge, and of the processes 

 by which it is obtained, is often involved by a confused apprehen- 

 sion of the import of the different classes of Words and Assertions, 

 will not regard these discussions as either frivolous or irrelevant to 

 the topics considered in the latter Books. 



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

 generalising the modes of investigating truth and estimating evidence, 

 by which so many important and recondite laws of nature have, in the 

 various sciences, 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 Archbisliop Wluitely, and the author 

 of a celebrated article on Bacon in the Edinhiirgh Review) have not 

 scrupled to pronounce it impossible.* The author has endeavoured 

 to combat their theory in the manner in Avliich Diogenes confuted the 

 sceptical reasonings against the possibility of motion ; remembering 

 that Diogenes' argument would have been equally conclusive, thongh 

 his individual perambulations might not have extended beyond the 

 circuit of his own tub. 



Whatever may be the value of what tlie author has succeeded in 

 effecting 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 pro- 

 cesses of physical science, which have been published within the last 

 few years. To these treatises, and to their authors, he has endeavoured 

 to do justice in the body of the work. But as with one of these 



* 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 cannot 

 be laid dow^n, or that tbey 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, liowever, being 

 the express object of the portion of the present work which treats of Induction, the 

 words in the text are no overstatement of the difference of opinion between Arch- 

 bishop Whately and me on the subject. 



