After the suitability of a physical objective has been established, as well as the feasibility of the contemplated action with relation thereto, such action is next considered from the standpoint of acceptability with reference to the consequences as to costs. The specific factors involved in acceptability as to consequences have previously been mentioned (page 31). * * * * * When the requirements of suitability, feasibility, and acceptability have been satisfied, the locality, the opposing force, or other subject of consideration may be regarded as a correct physical objective. When more than one correct physical objective has been determined and a choice is indicated, such selection will also be founded on the foregoing requirements. No doctrine, no advance instructions, can replace the responsible judgment of a commander as to his correct physical objectives. On occasion, higher authority may request recommendations (see page 42, as to opinions) with respect to such objectives. The duty of a commander to depart from his instructions under certain conditions, and the grave responsibility which he thereby assumes, have also been referred to (page 16). Relative Positions Fundamental Considerations. The relative positions occupied or susceptible of occupancy by armed forces are matters which demand constant and intelligent attention before and during hostilities. Being fruitful sources of advantage or disadvantage, such relative positions assume primary importance where enemy forces are concerned, and are scarcely of less importance from the standpoint of the correct apportionment of the subdivisions of one's own forces, and from the viewpoint of their freedom of action. During periods of actual tactical contact, the successful delivery of the decisive thrust against selected physical objectives is greatly furthered by the occupancy and maintenance of advantageous relative positions. The fundamental significance of relative position lies in the fact that position is the basis of movement, for movement is merely a change of position. Speed is the rate at which movement takes place. The particular factors to be reckoned with are, therefore, time and space. In skillful utilization of these elements lies the successful employment of relative position in the creation or maintenance of a favorable military situation, whether the movement be by land, sea, or air (page 46).