xxvi PKEl'ACE TO THE 'SECOND EDITION. 



psychological and philosophical analysis. u If the book 

 really corresponded to its title, Mr. Jevons could hardly 

 have passed so lightly over the question, which he does 

 not omit to raise, concerning those undoubted principles 

 of knowledge commonly called the Laws of Thought .... 

 Everywhere, indeed, he appears least at ease when he 

 touches on questions properly philosophical ; nor is he 

 satisfactory in his psychological references, as on pp. 4, 5, 

 where he cannot commit himself to a statement without 

 an accompaniment of ' probably,' ' almost,' or ' hardly.' 

 Reservations are often very much in place, but there are 

 fundamental questions on which it is proper to make up 

 one's mind." 



These remarks appear to me to be well founded, and I 

 must state why it is that I have ventured to publish an 

 extensive work on logic, without properly making up my 

 mind as to the fundamental nature of the reasoning 

 process. The fault after all is one of omission rather than 

 of commission. It is open to me on a future occasion to 

 supply the deficiency if I should ever feel able to under- 

 take the task. But I do not conceive it to be an essential 

 part of any treatise to enter into an ultimate analysis of 

 its subject matter. Analyses must always end somewhere. 

 There were good treatises on light which described the 

 laws of the phenomenon correctly before it was known 

 whether light consisted of undulations or of projected 

 particles. Now we have treatises on the Undulatory 

 Theory which are very valuable and satisfactory, although 

 they leave us in almost complete doubt as to what the 

 vibrating medium really is. So I think that, in the 

 present day, we need a correct and scientific exhibition 

 of the formal laws of thought, and of the forms of 

 reasoning based on them, although we may not be able 

 to enter into any complete analysis of the nature of those 

 laws. What would the science of geometry be like now 

 if the Greek geometers had decided that it was improper 

 to publish any propositions before they had decided on 



