It may be objected that though the questions selected are most important _in themselves_, there are other things more worth thinking about, because of the mental discipline they yield. Now putting aside the fact that questions important in themselves should be dealt with ultimately—that mental discipline would be useless unless applied to important problems—I must voice my suspicion that the most useful questions are also the best for training the mind. It may be true that punching the bag will help a prizefighter in boxing. But other things equal, a man who has spent one week in actual boxing is better prepared to enter the prize ring than one who has devoted a month to bag punching. The best practice for boxing is boxing. The best practice for solving important questions is solving important questions. Nor do I admit the contention is valid that one problem rather than another should be thought of because it is “deeper.” We cannot truthfully say that psychology is a “deeper” science than ethics, or that metaphysics is deeper than psychology, or vice versa. Most subjects and most problems are just as deep as we care to make them. Their depth depends entirely on how deep we go into them. This applies especially to the so-called philosophical sciences. We may give them shallow treatment or we may give them profound treatment. But we shall usually find that the deepest questions are the most important questions. For the most important questions have generally attracted the greatest minds; consequently they have been given the deepest treatment; and when a man reads the attempted solutions of these great minds his thoughts tend toward this deeper plane. Of course certain problems, especially in mathematics, can be dealt with by only one method. In this case we may properly speak of some problems being objectively deeper or at least more difficult than others. Some objections may be offered to several of the questions in my list, on the ground that they are invalid. Such problems as the immortality of the soul and the problem of existence may be declared inscrutable, unsolvable. Such a problem as “Is society for the benefit of the individual or is the individual for the benefit of society?” may be said to imply that society is something which has been voluntarily formed like the State. It may be declared that this is not the case; it may be objected that this question is meaningless. All these objections may be justified. But their truth cannot be determined until we actually attempt a solution. The determination of the validity of a problem is part of the problem. * * * * * We come now to the question of what is most worth reading. The simplest answer is that that is most worth reading which is most worth thinking about, and therefore we should read those books which deal with such problems as I have indicated. But this counsel needs to be supplemented.