viii PREFACE TO THE FIRST EDITION. 



made the practice-ground of the reasoning powers, because 

 they furnish us with a great body of precise and successful 

 investigations. In these sciences we meet with happy 

 instances of unquestionable deductive reasoning, of ex- 

 tensive generalisation, of happy prediction, of satisfactory 

 verification, of nice calculation of probabilities. We can 

 note how the slightest analogical clue has been followed 

 up to a glorious discovery, how a rash generalisation has 

 at length been exposed, or a conclusive expcrimcntum 

 crucis has decided the long-continued strife between two 

 rival theories. 



In following out my design of detecting the general 

 methods of inductive investigation, I have found that the 

 more elaborate and interesting processes of quantitative 

 induction have their necessary foundation in the simpler 

 science of Formal Logic. The earlier, and probably by 

 far the least attractive part of this work, consists, there- 

 fore, in a statement of the so-called Fundamental Laws 

 of Thought, and of the all-important Principle of Substi- 

 tution, of which, as I think, all reasoning is a develop- 

 ment. The whole procedure of inductive inquiry, in its 

 most complex cases, is foreshadowed in the combinational 

 view of Logic, which arises directly from these fundamental 

 principles. Incidentally I have described the mechanical 

 arrangements by which the use of the important form 

 called the Logical Alphabet, and the whole working of 

 the combinational system of Formal Logic, may be ren- 

 dered evident to the eye, and easy to the mind and 

 hand. 



The study both of Formal Logic and of the Theory of 

 Probabilities has led me to adopt the opinion that there 

 is no such thing as a distinct method of induction as 

 contrasted with deduction, but that induction is simply 

 an inverse employment of deduction. Within the last 

 century a reaction has been setting in against the purely 

 empirical procedure of Francis Bacon, and physicists have 



