The various wants of man are sometimes classified as necessities, comforts, and luxuries, but all economists take care to emphasize that these terms have only relative meanings which, in the rapidly changing conditions of modern life, are changing constantly. The comforts of one generation, or of one country, become the necessities in another; and luxuries becoming comforts, are looked upon finally as necessities. And as the desires grow, they more and more alter the world. Man has changed the face of the earth; he has affected its climate, its fertility, its beauty, because, either for better or for worse, his desires have impressed themselves upon the world about him. [Sidenote: Wants must precede wealth] 5. _In human society the growth of wants is necessary to progress._ From the earliest times teachers of morals have argued for simplicity of life and against the development of refinements. We do not now raise the moral question, but there is no doubt that the economic effect of developing wants is in the main to impel to greater effort. They are the mainspring of economic progress. In recent discussion of the control of the tropics, the too great contentedness of tropical peoples has been brought out prominently. Some one has said that if a colony of New England school-teachers and Presbyterian deacons should settle in the tropics, their descendants would, in a single generation, be wearing breech-clouts and going to cock-fights on Sunday. Certain it is that the energy and ambition of the temperate zone are hard to maintain in warmer lands. The negro's content with hard conditions, so often counted as a virtue, is one of the difficulties in the way of solving the race problem in our South to-day. Booker T. Washington, and others who are laboring for the elevation of the American negroes, would try first to make them discontented with the one-room cabins, in which hundreds of thousands of families live. If only the desire for a two- or three-room cabin can be aroused, experience shows that family life and industrial qualities may be improved in many other ways. [Sidenote: But impossible hopes lessen gratifications] Not only in America, but in most civilized lands to-day, is seen a rapid growth of wants in the working-classes. The incomes and the standard of living have become increasing, but not so fast as have the desires of the working-classes. Regret has been expressed by some that the workers of Europe are becoming "declassed." Increasing wages, it is said, bring not welfare, but unhappiness, to the complaining masses. If discontent with one's lot goes beyond a moderate degree, if it is more than the desire to better one's lot by personal efforts, if it becomes an unhappy longing for the impossible, then indeed it may be a misfortune. But a moderate ambition to better one's condition is the "divine discontent" absolutely indispensable if energy and enterprise are to be called into being.