This Clausewitz considers most important. He says that "Knowledge of the conduct of war ... _must pass completely into the mind_, and almost cease to be something objective." For in war "The moral reaction, the ever-changing form of things makes it necessary for the chief actor to carry _in himself_ the whole mental apparatus of his knowledge, in order 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." * * * * * So much for Clausewitz, therefore, as the greatest yet the simplest and least theoretical of theorists on war. Mark well his comforting dictum that "Theory is nothing but rational reflection upon all the situations in which we can be placed in war." That is a task which we have all more or less attempted. Therefore we are all more or less theorists. The only question is that of comparative "thoroughness" in our reflections. And it is essentially this "thoroughness" in investigation and reflection towards which Clausewitz helps us. Like every other habit, the _habit_ of military reflection gradually grows with use; till, fortified and strengthened by detailed knowledge, it gradually becomes Power. REFLECTIONS The theory of war is simple, and there is no reason why any man who chooses to take the trouble to read and reflect carefully on one or two of the acknowledged best books thereon, should not attain to a fair knowledge thereof. He may with reasonable trouble attain to such knowledge of the theory of war as will enable him to follow with intelligent appreciation the discussions of experienced soldier or soldiers. Such knowledge as will prevent his misunderstanding the experienced soldier's argument from pure ignorance, and such knowledge as will enable him to understand the military reasons put forward and the military object proposed. To the opinion of such a man all respect will be due. Thus, and thus only. It is indeed the plain duty of all who aspire to rule either thus to qualify themselves to understand, or else to abstain from interference with, the military interests of the State. CHAPTER V THE MAGNITUDE OF THE EFFORT REQUIRED IN A MODERN NATIONAL WAR This point is here illustrated with more detail from Clausewitz than may seem necessary to some, because it is precisely the point regarding modern war which is least understood in this country.