Venn, best known for his diagrams for set theory, primarily studied logic and probability theory. The present book is a study of the principles of logic, with special emphasis on inference and induction. From the Preface to the first edition (1889): 'As many readers will probably perceive, the main original guiding influence with me - as with most of those of the middle generation, and especially with most of those who approached logic with previous mathematical or scientific training - was that of Mill...I still continue to regard the general attitude towards phenomena, which Mill took up as a logician, to be the soundest and most useful for scientific study'.From the Preface to the Second Edition (1907): 'Though thus leaving the main outlines unaltered I have done what I could to improve the work, and to try to bring it up to date...A number of paragraphs have been altered, others have been re-written, and many hundreds of minor alterations, additions and corrections inserted'.