Since the earliest days, man has attempted to formulate the relationships between causes and effects without, however, always possessing the specific knowledge essential to accuracy. Pithy statements have always had great appeal to man, as evidenced by the existence of proverbs, maxims, and adages preserved from times of great antiquity. Frequently, however, such statements are not expressive of the truth. Sometimes, again, they state facts, without, nevertheless, expressing the whole truth. Only when the relationship between cause and effect has been demonstrated to be always true can the trained, inquiring mind receive its statement as a valid guide, acceptable as a principle in the light of the knowledge of the day. To rely upon rules of action which do not express the whole truth is to court the danger of encountering exceptions which may entail serious consequences. The value of those rules known to be inexpressive of the whole truth lies in the fact that they may invite attention to circumstances which are sometimes encountered, or may suggest methods of action which are sometimes appropriate. Danger lies in the fact that such rules may fail to give proper emphasis to other circumstances or other methods which are encountered or are more appropriate in other cases. Such a rule may fail to consider the entire problem. Its use, therefore, implies the necessity of recognizing cases to which it is not applicable. This may frequently be difficult in the active operations of war, when nervous strain and the urgency of events are handicaps to quick and accurate thinking (see page 22). To express the whole truth, a rule of action calls to attention all circumstances, or causes, which may ever influence the result. The saying that "the exception proves the rule" is properly interpreted only in the older sense that an exception "tests" the rule, indicating by the mere fact of exception that the rule is to such extent incomplete. Subject to variations of phraseology, the old adage "circumstances alter cases" is the sole reliable and fundamental rule of action. A corresponding maxim of the military profession, "It depends on the situation", has its root in recognition of the same fact, i.e., that the action taken in any situation depends, properly, on the circumstances of the case, and that the relationship between cause and effect (page 22) is always the governing consideration. The principles deduced hereafter (Chapter III) have these irrefutable findings as their foundation.