That the true nature of a war should be realised by contemporaries as clearly as it comes to be seen afterwards in the fuller light of history is seldom to be expected. At close range accidental factors will force themselves into undue prominence and tend to obscure the true horizon. Such error can scarcely ever be eliminated, but by theoretical study we can reduce it, nor by any other means can we hope to approach the clearness of vision with which posterity will read our mistakes. Theory is, in fact, a question of education and deliberation, and not of execution at all. That depends on the combination of intangible human qualities which we call executive ability.

This, then, is all the great authorities ever claimed for theory, but to this claim the chief of them at least, after years of active service on the Staff, attached the highest importance. "In actual operations," he wrote in one of his latest memoranda, "men are guided solely by their judgment, and it will hit the mark more or less accurately according as they possess more or less genius. This is the way all great generals have acted.... Thus it will always be in action, and so far judgment will suffice. But when it is a question not of taking action yourself, but of convincing others at the Council table, then everything depends on clear conceptions and the exposition of the inherent relations of things. So little progress has been made in this respect that most deliberations are merely verbal contentions which rest on no firm foundation, and end either in every one retaining his own opinion, or in a compromise from considerations of mutual respect—a middle course of no actual value."

The writer's experience of such discussions was rich and at first hand. Clear conceptions of the ideas and factors involved in a war problem, and a definite exposition of the relations between them, were in his eyes the remedy for loose and purposeless discussion; and such conceptions and expositions are all we mean by the theory or the science of war. It is a process by which we co-ordinate our ideas, define the meaning of the words we use, grasp the difference between essential and unessential factors, and fix and expose the fundamental data on which every one is agreed. In this way we prepare the apparatus of practical discussion; we secure the means of arranging the factors in manageable shape, and of deducing from them with precision and rapidity a practical course of action. Without such an apparatus no two men can even think on the same line; much less can they ever hope to detach the real point of difference that divides them and isolate it for quiet solution.