viii PREFACE. 



question concerning the importance of attention 

 to the best practice in matters of reasoning. 



Some of the reasons which induced me to 

 select Darwin's works as a basis for an analysis 

 of scientific method were: (i) the desire to 

 confine the discussion to the writings of a single 

 author, in order to concentrate the reader's at- 

 tention upon a model; (2) the fact that his 

 works cover a wide range of subjects, and can 

 be read and understood by those who have had 

 only a moderate amount of scientific training; 

 and (3) above all, the fact that Darwin's inves- 

 tigations, and the reasoning based upon them, 

 have furnished the biological sciences with their 

 dominant principles. 



To facilitate the study of his works from the 

 point of view of method, references have been, 

 added to nearly all the examples drawn from 

 them. A few examples have been mentioned 

 or briefly discussed several times, and this may 

 detract slightly from the freshness of some parts ; 

 but a partial compensation may be found in the 

 fact that the repetition of the same example, 

 under different divisions of the subject, will 

 emphasize more strongly the complex inter- 



