Does this, however, prevent us establishing, on the basis of the facts exposed in the preceding chapter, a general principle sufficiently definite to serve as a practical guide in policy, and to indicate reliably a general tendency in human affairs? Assuredly not. The principle which explains the uselessness of much of the force exerted by the military type of empire, and justifies in large part that employed by Britain, is neither obscure nor uncertain, although empiricism, rule of thumb (which is the curse of political thinking in our days, and more than anything else stands in the way of real progress), gets over the difficulty by declaring that no principle in human affairs can be pushed to its logical or theoretical conclusion; that what may be "right in theory" is wrong in practice. Thus Mr. Roosevelt, who expresses with such admirable force and vigor the average thoughts of his hearers or readers, takes generally this line: We must be peaceful, but not too peaceful; warlike, but not too warlike; moral, but not too moral.[87] By such verbal mystification we are encouraged to shirk the rough and stony places along the hard road of thinking. If we cannot carry a principle to its logical conclusion, at what point are we to stop? One will fix one and another will fix another with equal justice. What is it to be "moderately" peaceful, or "moderately" warlike? Temperament and predilection can stretch such limitations indefinitely. This sort of thing only darkens counsel. If a theory is right, it can be pushed to its logical conclusion; indeed, the only real test of its value is that it _can_ be pushed to its logical conclusion. If it is wrong in practice, it is wrong in theory, for the right theory will take cognizance of all the facts, not only of one set. In Chapter II. of this part (pp. 186-192), I have very broadly indicated the process by which the employment of physical force in the affairs of the world has been a constantly diminishing factor since the day that primitive man killed his fellow-man in order to eat him. Yet throughout the whole process the employment of force has been an integral part of progress, until even to-day in the most advanced nations force--the police-force--is an integral part of their civilization. What, then, is the principle determining the advantageous and the disadvantageous employment of force? Preceding the outline sketch just referred to is another sketch indicating the real biological law of man's survival and advance; the key to that law is found in co-operation between men and struggle with nature. Mankind as a whole is the organism which needs to co-ordinate its parts in order to insure greater vitality by better adaptation to its environment.