The best plan, selected accordingly, is then incorporated into a decision as to the procedure to be adopted. This decision is then available as a general plan, or may be developed into one, to serve as a basis if necessary for a more detailed plan for the attainment of the appropriate effect desired. Later development, herein, of the details of this procedure will disclose many ramifications. The treatment, so far, points to the fact that the best method of reaching sound decision is through systematic thought which employs logic, i.e., sound reasoning, as its machinery. The Necessity for Logical Thought. Logical thought separates the rational from the irrational. Its use avoids the wastefulness of the trial-and-error method. By its insistent employment, dormant powers of reasoning are awakened, and the danger that attends instinctive, spontaneous, impulsive, or emotional acceptance of conclusions (page 9) is lessened. The evil effects of an inclination to dodge the issue or of a disinclination to face the facts are thus also avoided. The fallacy of employing the reasoning power to justify conclusions already reached, whether on the basis of tradition or habit, or because of the bias or bent of a school of thought, or because of the tendency of human nature to accept plausible suggestions, is also made apparent. Through the deliberate practice of testing and weighing, the faculty of arriving swiftly at accurate decisions is strengthened and is brought more quickly into play when time is a matter of immediate concern. Principles in their Relation to Logical Thought. Because of the necessity for the exercise of judgment (page 3) in the systematic arrangement of thought, the relationship between cause and effect, as expressed in principles, is of great assistance in applying logical processes to the problems of human life. A principle establishes a correct relation between cause and effect. The word, derived from the Latin "principium", meaning a foundation, beginning, source, origin, or cause, has, because a cause implies an effect, acquired in correct usage the significance of a true statement of relationship between cause and effect. A principle, so formulated, is a natural law (page 19) because it expresses a fact of nature; it thus becomes a reliable rule of action and may be confidently adopted as a governing law of conduct. If basic in its field, such a rule or law becomes a general or fundamental principle with respect thereto; each such basic truth may be the basis for the determination of many corollary or subordinate principles dealing with the details of the particular subject.