There is a great practical truth in the mental law of sale now generally accepted by business psychologists and by practical men in the business world. This mental law of sale holds true in all kinds of persuasion because it describes the process of the human mind as it proceeds, step by step, from indifference or antagonism to favorable action. It is, therefore, impossible to discuss intelligently the ways and means of successful persuasion, except upon a basis of this law. Here is the law: [10]"Favorable attention properly sustained changes into interest, interest properly intensified changes into desire, desire properly augmented ripens into decision and action." [Footnote 10: From "The Science of Business Building," by A.F. Sheldon.] FAVORABLE ATTENTION Now, it is known to psychologists that certain sensations attract favorable attention in a larger number of cases than others. For example, in an appeal to the eye, rectangular shape in proportion of three to five, that is to say, three units of measurement wide by five units of measurement long is more likely to attract favorable attention than a square. Similarly, any object in motion or having the illusion of motion, is more likely to attract favorable attention than an object at rest. Black letters upon a white background attract more favorable attention than white letters upon a black background. Many such psychological problems have been worked out. They are valuable, but they have no place in this work, since our task here is not to deal with averages, but rather with variations in individuals--how to discern them and how to deal with them. INTEREST In a similar way, psychologists have determined that the average individual more quickly becomes interested in that which he can understand than in that which he cannot understand, in that which appeals to something in his own experience than in that which has no such appeal, in that which appeals to his tastes and his feelings than in that which appeals to his judgment. These are rules applicable to the average, but they are very general and are of little use to you unless you add to them specific knowledge of every individual whom you wish to persuade. DESIRE