During the planned action, a change in the situation may have the effect of challenging the integrity of the basic plan. The commander is then faced by a problem calling for the exercise of the highest order of ability. While problems of this type probably occur with least frequency, they are the most important of those which may be encountered during the fourth step. Because such a problem, arising from the demands of a new situation, requires a re-estimate of the basic situation, the essential procedure is the same as for a basic problem (Chapter VI), but certain modifications necessarily appear. Summary of the Situation. While a commander will rarely find himself operating without instructions, the importance of problems arising when no directive applies is not lessened by the fact that such problems may infrequently occur. When the commander is faced with a situation not covered in orders of his superior, action may be necessary before he can inform higher authority and receive instructions. Usually this situation will be an emergency. Often it will not allow time for a written estimate. The fact that such a situation has arisen, and the reasons causing the commander to conclude that it has arisen, are appropriately included in Section I-A of the Estimate, under the "Summary of the Situation". Recognition of the Incentive. The conclusion on the part of the commander that the situation requires him to make provision for its maintenance, or for a change, which in either case calls for a departure from his basic Decision, constitutes a recognition of his new incentive. Appreciation of the Objective. Frequently the new incentive will indicate that the objective embodied in the commander's present task is no longer suitable, but that the purpose of his mission still applies. By modifying the objective indicated in his assigned task, but adhering to that in the purpose of his mission, he may be able to visualize a new objective which will be appropriate to the new circumstances. In this case the retained purpose assists the commander to select a new objective which he can confidently adopt as the basis for a new task which he assigns to himself. If neither the commander's task nor the purpose of his mission apply in the new situation, the evolution of a proper new objective may be much more difficult. Under such circumstances the commander, by the use of such information as may be in his possession, will first endeavor to deduce an objective whose attainment constitutes a suitable purpose. Such a deduction will be made on the basis of the larger circumstances of the war, the campaign, or the operation. Having made this determination, the commander will then deduce a task appropriate to the new situation and in furtherance of the adopted purpose. (See Chapter IV, page 52.)