If a man of expertness spends half his life in the endeavour to clear up an obscure subject thoroughly, he will probably know more about it than a person who seeks to master it in a short time. Theory is instituted that each person in succession may not have to go through the same labour of clearing the ground and toiling through his subject, but may find the thing in order, and light admitted on it. It should educate the mind of the future leader in War, or rather guide him in his self-instruction, but not accompany him to the field of battle; just as a sensible tutor forms and enlightens the opening mind of a youth without, therefore, keeping him in leading strings all through his life. If maxims and rules result of themselves from the considerations which theory institutes, if the truth accretes itself into that form of crystal, then theory will not oppose this natural law of the mind; it will rather, if the arch ends in such a keystone, bring it prominently out; but so does this, only in order to satisfy the philosophical law of reason, in order to show distinctly the point to which the lines all converge, not in order to form out of it an algebraical formula for use upon the battle-field; for even these maxims and rules serve more to determine in the reflecting mind the leading outline of its habitual movements than as landmarks indicating to it the way in the act of execution. 28. BY THIS POINT OF VIEW THEORY BECOMES POSSIBLE, AND CEASES TO BE IN CONTRADICTION TO PRACTICE. Taking this point of view, there is a possibility afforded of a satisfactory, that is, of a useful, theory of the conduct of War, never coming into opposition with the reality, and it will only depend on rational treatment to bring it so far into harmony with action that between theory and practice there shall no longer be that absurd difference which an unreasonable theory, in defiance of common sense, has often produced, but which, just as often, narrow-mindedness and ignorance have used as a pretext for giving way to their natural incapacity. 29. THEORY THEREFORE CONSIDERS THE NATURE OF ENDS AND MEANS—ENDS AND MEANS IN TACTICS. Theory has therefore to consider the nature of the means and ends.