Take an analogous example, and the province of strategical theory becomes clear at once. Navigation and the parts of seamanship that belong to it have to deal with phenomena as varied and unreliable as those of the conduct of war. Together they form an art which depends quite as much as generalship on the judgment of individuals. The law of storms and tides, of winds and currents, and the whole of meteorology are subject to infinite and incalculable deflections, and yet who will deny nowadays that by the theoretical study of such things the seaman's art has gained in coherence and strength? Such study will not by itself make a seaman or a navigator, but without it no seaman or navigator can nowadays pretend to the name. Because storms do not always behave in the same way, because currents are erratic, will the most practical seaman deny that the study of the normal conditions are useless to him in his practical decisions? If, then, the theoretical study of strategy be approached in this way--if, that is, it be regarded not as a substitute for judgment and experience, but as a means of fertilising both, it can do no man harm. Individual thought and common-sense will remain the masters and remain the guides to point the general direction when the mass of facts begins to grow bewildering. Theory will warn us the moment we begin to leave the beaten track, and enable us to decide with open eyes whether the divergence is necessary or justifiable. Above all, when men assemble in Council it will hold discussion to the essential lines, and help to keep side issues in their place. But beyond all this there lies in the theory of war yet another element of peculiar value to a maritime Empire. We are accustomed, partly for convenience and partly from lack of a scientific habit of thought, to speak of naval strategy and military strategy as though they were distinct branches of knowledge which had no common ground. It is the theory of war which brings out their intimate relation. It reveals that embracing them both is a larger strategy which regards the fleet and army as one weapon, which co-ordinates their action, and indicates the lines on which each must move to realise the full power of both. It will direct us to assign to each its proper function in a plan of war; it will enable each service to realise the better the limitations and the possibilities of the function with which it is charged, and how and when its own necessities must give way to a higher or more pressing need of the other. It discloses, in short, that naval strategy is not a thing by itself, that its problems can seldom or never be solved on naval considerations alone, but that it is only a part of maritime strategy--the higher learning which teaches us that for a maritime State to make successful war and to realise her special strength, army and navy must be used and thought of as instruments no less intimately connected than are the three arms ashore.