If, to take a further example, the known factors include the appropriate effect desired, the means opposed, the physical conditions prevailing in the field of action, and the consequences as to costs, the only unknown remains the means available. The question then is, what means need be made available for the accomplishment of the contemplated effort? The answer to this question may be found in the application of what may be called the principle for the determination of the proper means to be made available in human affairs,--as follows: In any human activity, the proper means to be made available depend on fulfillment of the requirements of Suitability of the means (in kind and amount) to accomplish the end in view, as determined by the factor of the appropriate effect desired, Feasibility of the effort to make such means available on the basis of comparative resources as determined by the factor of the means opposed, influenced by the factor of the physical conditions prevailing in the field of action, and Acceptability of the results of the effort involved, as determined by the factor of the consequences as to costs. * * * * * The influence of physical conditions in the field of action may be illustrated by any case where ends otherwise feasible of attainment cannot be achieved without effecting changes in such conditions. The resolution of the uncertainty then requires study to determine what suitable changes can be made. Changes for such a purpose may take various forms, such as the construction of physical features in the area involved, or the destruction of such features already existing; or, again, both methods may be employed. Examples of such changes have existed and still exist in profusion, some of them, military and non-military, being on such a scale as radically to alter the previous status with respect to entire nations. The question as to what changes ought to be effected in the prevailing physical conditions, in order to attain a certain objective, can be answered by the application of what may be called the principle for the determination of the proper physical conditions to be established in the field of action,--as follows: In any human activity, the proper physical conditions to be established in the field of action depend on fulfillment of the requirements of Suitability of such conditions to the end in view, as determined by the factor of the appropriate effect desired, Feasibility of effort to establish such conditions, on the basis of comparative resources, as determined by the factors of the means available and opposed, influenced by the factor of the physical conditions existing in the field of action, and Acceptability of the results of the effort involved, as determined by the factor of the consequences as to costs.