The volume includes Mark Twain's previously published philosophical writing. Fictional pieces (even some which develop arguments contained here) are ordinarily excluded, as are other works appropriate to different volumes in this edition. However, Letter from the Recording Angel, The Five Boons of Life, and Letters from the Earth, although they are in a strict sense fictional, have been judged more relevant to the present volume that to the volumes of short fiction. Things a Scotsman Wants to Know, previously unpublished, is included by agreement with the editor of The Mark Twain Papers, as being especially relevant to themes of this volume. Other unpublished items appear as supplements because of their close relation to What Is Man?, Christian Science, and 'The Turning Point of My Life.' The two works that break off with unfinished sentences, Bible Teaching and Religious Practice and the introductory section of Letters from the Earth, were abandoned by the author or else their endings have been lost. The order of works in this volume is according to date of publication or, for those unpublished during the author's lifetime, date of composition. For works published during his lifetime, dates of first publication appear in roman type below titles; for works first published after his death, date are in italics and indicate time of composition.