The formulation of a principle, therefore, requires the determination of the causes that generate a particular effect (or effects), and the accurate expression of the resultant relationship. Such expression frequently takes the form of a proportion. In the mathematical sciences the proportion may represent a precise balance; its statement may be an exact formula. In other sciences, a definite relationship between cause and effect has likewise been established in many cases, though not always with mathematical precision. Comparable exactitude has not been attained, in some cases, because the field has not been so thoroughly explored; moreover, greater difficulty is experienced, at times, in isolating the cause, or causes. The balance represented by such equations, therefore, is based on quantities whose weights vary within wide ranges. (See page 3.) Human conduct does not lend itself to analysis as readily as do mathematical and physical phenomena. The advance in the psychological and sociological sciences is not so marked as in the physical, and the actions and reactions of the mind of man have not yet proved to be susceptible of reduction to exact formulae. Nevertheless, man, in his intuitive search for valid guides for his own action, has been able, with the advance of time, greatly to improve his own lot through the medium of the scientific approach to human problems. The insistent search of the human mind for reliable rules of action is a recognized natural phenomenon. As understood on the basis of expert investigation of the subject, this trait results from the recognition, conscious or otherwise, by countless generations of mankind, of the relationships between cause and effect as evidenced in the workings of the laws of nature (page 22). A logical outcome, therefore, of experience, this instinctive demand of the mind constitutes a force which defies opposition. Properly utilized, this force affords a powerful and natural aid in the solution of problems. Inasmuch as a valid rule, or principle, is of great assistance in arriving at sound decisions and in formulating effective plans (see page 22), this demand for reliable guides is logical, as well as natural. In any event, the demand for such guidance, if not met by provision for reliable rules of action, may result in the adoption of faulty rules, with frequent unfortunate consequences. The formulation of principles, already referred to in this connection, constitutes in itself a recognized problem (see also page 27) of great difficulty; for it is a human failing to avoid the mental effort involved in thinking through such a problem, and to rely on rules whose plausibility and seeming simplicity are frequently a measure of their incompleteness and inaccuracy.