From the preface to the first edition: It will be seen that I have made comparatively slight reference to other, and especially to contemporary writers. In my former works the opposite course was adopted, but for special reasons. As regards Probability, much had recently been produced which was only accessible in scattered numbers of various scientific journals, and every student knows how apt these are to be overlooked unless special attention be directed to them. And as regards Symbolic Logic, the history and literature of the subject had been so entirely neglected that even the names of most previous writers on the subject were quite unknown to their modern successors. By John Venn, a British logician and philosopher of the nineteenth and early twentieth centuries.