Now we have yet to consider one condition which is more necessary for the knowledge of the conduct of War than for any other, which is, that it must pass completely into the mind and almost completely cease to be something objective. In almost all other arts and occupations of life the active agent can make use of truths which he has only learnt once, and in the spirit and sense of which he no longer lives, and which he extracts from dusty books. Even truths which he has in hand and uses daily may continue something external to himself, If the architect takes up a pen to settle the strength of a pier by a complicated calculation, the truth found as a result is no emanation from his own mind. He had first to find the data with labour, and then to submit these to an operation of the mind, the rule for which he did not discover, the necessity of which he is perhaps at the moment only partly conscious of, but which he applies, for the most part, as if by mechanical dexterity. But it is never so in War. The moral reaction, the ever-changeful form of things, makes it necessary for the chief actor to carry in himself the whole mental apparatus of his knowledge, that anywhere and at every pulse-beat he may be capable of giving the requisite decision from himself. Knowledge must, by this complete assimilation with his own mind and life, be converted into real power. This is the reason why everything seems so easy with men distinguished in War, and why everything is ascribed to natural talent. We say natural talent, in order thereby to distinguish it from that which is formed and matured by observation and study. We think that by these reflections we have explained the problem of a theory of the conduct of War; and pointed out the way to its solution. Of the two fields into which we have divided the conduct of War, tactics and strategy, the theory of the latter contains unquestionably, as before observed, the greatest difficulties, because the first is almost limited to a circumscribed field of objects, but the latter, in the direction of objects leading directly to peace, opens to itself an unlimited field of possibilities. Since for the most part the Commander-in-Chief has only to keep these objects steadily in view, therefore the part of strategy in which he moves is also that which is particularly subject to this difficulty. Theory, therefore, especially where it comprehends the highest services, will stop much sooner in strategy than in tactics at the simple consideration of things, and content itself to assist the Commander to that insight into things which, blended with his whole thought, makes his course easier and surer, never forces him into opposition with himself in order to obey an objective truth. CHAPTER III. Art or Science of War 1.—USAGE STILL UNSETTLED (POWER AND KNOWLEDGE. SCIENCE WHEN MERE KNOWING; ART, WHEN DOING, IS THE OBJECT.)