But reputation does not furnish the only means of selecting. By merely glancing through a book, stopping here and there to read entire paragraphs—a task of ten or fifteen minutes—we can form an estimate which later reading will usually justify. For an author betrays himself in every line he writes; every slightest remark reveals in some manner the breadth and depth of his thought. But just how well we can judge a book in this way depends both on our own ability and on the time we devote to glancing through it. A few general requirements in a main text have been implied in stating the purpose of having one. The book with the best reputation is not necessarily the best for you. In economics Adam Smith’s _Wealth of Nations_, though easily the most famous book on the subject, would hardly be suitable as a main text because it has been superseded. But though recency is always an asset, this does not mean that the most recent book is always or even usually the best. The common idea, though it is usually but vaguely formulated, is that the writer of the more recent book has had all the previous books to draw upon, and has therefore been able to extract the best from all of them and add to this his own thoughts. The fallacy of this has been pointed out in the trenchant language of Schopenhauer: “The writer of the new book often does not understand the old books thoroughly, and yet he is unwilling to take their exact words; so he bungles them and says in his own bad way that which has been said very much better and more clearly by the old writers, who wrote from their own lively knowledge of the subject. The new writer frequently omits the best things they say, their most striking illustrations, their happiest remarks, because he does not see their value or feel how pregnant they are. The only thing that appeals to him is what is shallow and insipid.” The value of recency will depend on the subject; while it would be essential in aviation, its importance would be far less in ethics. It is not well to take as your main text a book presenting a number of different and conflicting viewpoints. One purpose of a main text is to avoid confusion. Do not start the study of psychology, for instance, by reading a history of the subject giving the views of different thinkers. Begin by taking up one definite system. Finally, be sure to select a book covering the entire field. Do not, for instance, take a volume on the tariff to begin the study of economics. * * * * * We pass now to the third step advised—to read critically. By this I do not mean that we should read skeptically or to confute everything an author says. I mean simply that we should resist our natural tendency to have our minds swayed by every opinion he expresses. I mean that before allowing an idea to slip into our minds we should first challenge its truth; we should examine its evidence.