While the list of courses of action given above is made up from the viewpoint of broad strategical problems, a similar list can be assembled for other problems. For example, the order, "Destroy enemy naval forces", if taken as the motivating task of a tactical estimate, will be the basis for certain courses of action, constituting, when complete (see below), a well-recognized general plan for a naval battle. This plan will in turn call for various detailed operations on the part of the several subdivisions of the force under the commander who makes the estimate (see page 95). As a tentative solution of the problem a course of action may be complete or partial, i.e., it may, if carried out, provide for the complete attainment of the objective; or, such complete attainment may require a combination of several of the courses of action under study. The exclusive consideration of courses of action of the complete type possesses the advantage of minimizing the total number of solutions under study. This simplifies the procedure of analysis and of comparing courses of action with each other, because of the relatively small number of courses to be tested and to be compared. However, it is frequently difficult, and sometimes impossible, to visualize complete courses of action, especially during the early stages of the estimate. Sometimes the initial visualization of partial courses and their eventual combination into a complete solution will be found necessary. Therefore, either or both of the foregoing systems of formulating courses of action may be found appropriate, according to individual preference and the nature of the particular problem. Individuals, comparable with respect to knowledge, appear to vary greatly in their ability to produce the appropriate suggestion, as to courses of action, at the right time. The reason for this phenomenon is not altogether clear, but it is known that thinking seems to be limited not merely by the range of knowledge, but by whatever part of it becomes available when needed. This point invites attention to another procedure which is open to the commander with respect to stimulating reflective thinking. This procedure recognizes the fact that, when two or more minds attack a problem, together, the combined effort often increases the applied mental power. This fact is universally recognized, for example, in the utilization of staff assistance (page 13). Inherent and acquired ability have unquestionably much to do with the possibilities of visualizing single courses of action with respect to their completeness as to attainment of the objective. One method of visualization seems to be the mental picturization of more or less detailed operations, followed by their combination, through rapid synthesis, into complete courses of action.