Description: The author of a book may be justified in believing that all his statements in the book are correct, at the same time believing that at least one of them is incorrect. The argument runs along these lines: It is customary for authors of academic books to include in the preface of their books statements such as "any errors that remain are my sole responsibility." Occasionally they go further and actually claim there are errors in the books, with statements such as "the errors that are found herein are mine alone." (1) Such an author has written a book that contains many assertions, and has factually checked each one carefully, submitted it to reviewers for comment, etc. Thus, he has reason to believe that each assertion he has made is true. (2) However, he knows, having learned from experience, that, despite his best efforts, there are very likely undetected errors in his book. So he also has good reason to believe that there is at least one assertion in his book that is not true. Thus, he has good reason, from (1), to rationally believe that each statement in his book is true, while at the same time he has good reason, from (2), to rationally believe that the book contains at least one error. Thus he can rationally believe that the book both does and does not contain at least one error.