The ideal of military command combines the best of human qualities with sound knowledge of the capabilities and limitations of the armed forces. It recognizes in war a form of human activity whose conduct, like that of all other human activities, is subject to natural law. It applies to the mastery of the problems of war, therefore, the natural mental processes of human thought (see Chapter II); it adapts these natural processes to a specific purpose, and consciously develops their use to the maximum degree for the attainment of this end. As command ascends the scale, its viewpoint broadens. Experience and added knowledge, with increasing authority and responsibility, lead to a concept of war more and more comprehensive, with the resultant growth in ability to evolve and put into effect a general plan for the effective control of collective effort. Unity of Effort. An objective is best attained by effective application of properly directed effort, exerted by a single individual or by groups of individuals. Where individuals are collectively concerned, unity of effort is the most important single factor contributory to the common success. The basic condition to be sought by the armed forces is an harmonious whole, capable of putting forth combined effort, intensified in strength because of the collective feature, and rendered effective by its unity. The Chain of Command. Within the limits of human capacity, an organization can exert its combined effort with greater effect the more closely the exercise of command represents the act of a single competent commander. To divide the supreme command in any locality, or to vest it in a body rather than in an individual, is necessarily to diffuse responsibility. In that degree there is then incurred the danger, through confusion of wills and ideas, of delaying decision and of creating corresponding diffusion of effort. Realization of this danger has led the military profession to entrust command, subject to justifiable exceptions (see page 71), to a single head, while ensuring, by careful selection and training of personnel, that competent individuals are available for this duty. Although this method is in seeming conflict with the restriction imposed by recognized limitations of human capacity, the difficulty is effectively met through the chain of command, whereby responsibility is assigned and authority is transmitted without lessening of ultimate responsibility. Responsibility and authority, the latter properly apportioned to the former, are inseparably inherent in command, and may not justifiably be severed from one another. In the abstract, the chain of command consists of a series of links, through which responsibility and authority are transmitted. The supreme commander is thus linked with his successively subordinate commanders, and all are disposed on, so to speak, a vertical series of levels, each constituting an echelon of command.