A Theory to be Practically Useful
Clausewitz insists that a useful theory cannot be more than a thorough knowledge of military history and "reflection upon all the situations in which we can be placed in war." "What genius does must be just the best of all rules, and theory cannot do better than to show just how and why it is so." "It is an analytical investigation of the subject which leads to 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. 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."[12]