27.  Theory must be of the nature of observations not of doctrine.

The second opening for the possibility of a theory lies in the point of view that it does not necessarily require to be a direction for action.  As a general rule, whenever an activity is for the most part occupied with the same objects over and over again, with the same ends and means, although there may be trifling alterations and a corresponding number of varieties of combination, such things are capable of becoming a subject of study for the reasoning faculties.  But such study is just the most essential part of every theory, and has a peculiar title to that name.  It is an analytical investigation of the subject that leads to an exact knowledge; and if brought to bear on the results of experience, which in our case would be military history, to a thorough familiarity with it.  The nearer theory attains the latter object, so much the more it passes over from the objective form of knowledge into the subjective one of skill in action; and so much the more, therefore, it will prove itself effective when circumstances allow of no other decision but that of personal talents; it will show its effects in that talent itself.  If theory investigates the subjects which constitute War; if it separates more distinctly that which at first sight seems amalgamated; if it explains fully the properties of the means; if it shows their probable effects; if it makes evident the nature of objects; if it brings to bear all over the field of War the light of essentially critical investigation—­then it has fulfilled the chief duties of its province.  It becomes then a guide to him who wishes to make himself acquainted with War from books; it lights up the whole road for him, facilitates his progress, educates his judgment, and shields him from error.

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.