Allied to politeness is the quality called Tact, which is defined as the "peculiar skill or adroitness in doing or saying exactly that which is required by, or is suited to, the circumstances; nice perception or discernment." A little consideration will show that Tact must depend upon an understanding of the viewpoint and mental attitude of the other person, so that if one has the key to the one he may open the door of the other. An understanding of the other person's position, and an application of the true spirit of politeness, will go a long way toward establishing the quality of tactfulness. Tact is a queer combination of Worldly Wisdom and the Golden Rule--a mixture of the ability to seek into the other person's mind, and the ability to speak unto others as you would that others speak unto you, under the same circumstances. The trait called Adaptability, or the faculty of adjusting oneself to conditions, and to the personality of others, also belongs to this category. Adaptability depends upon the ability to see the other person's position. As a writer says: "Those individuals who are out of harmony with their surroundings disappear to make room for those who are in harmony with them." When the keynote of the understanding of the minds of others is found, the whole subject of true politeness, tact and adaptability is understood and may be applied in practice. V. _Human Nature._ Closely allied to the subject of the preceding paragraphs, is that of Human Nature. A knowledge of Human Nature is very important to the Salesman. In order to understand the workings of the minds of others, one must not only understand the general psychological principles involved, but also the special manifestations of those principles. Nature tends to form classes and species, and the majority of people may be grouped into special classes depending upon their temperaments. An intelligent study of The New Psychology and the general subject of Human Nature in works on Physiognomy, etc., will do much to start one well upon the road to an understanding of Human Nature. But, after all, the best knowledge comes only when the general principles are tested and applied under observation in general experience.