Neither by itself has any claim to be distinguished as art. The ways in which a work of art can be organized are practically innumerable; but in musical art they all have the simple structural basis of a departure from a given point to a point or many points of contrast and back home again. The infinite number of varieties depends on the manner in which the central point is established, and how the departure from it is made; how the contrasting middle portion is organized, and how the return home is established. The evolution of principles of form consists in the elaboration of the main divisions into subordinate contrasts, contrasts to contrasts, inner organic procedures, devices of structure which are linked and superimposed on one another, in which the steps that lead away from the main centre are successively distributed in subtle gradations, all of which are available to make the adaptation to the idea more perfect. The story of the evolution is perspicuously clear, as the vast amount of devoted and, latterly, intelligent labor which has been expended upon collecting folk-songs and specimens of quasi-musical phrases of savages has completed the story from the first appearance of the desire for some kind of orderliness up to the portentous elaborations of European music of the present day. The way complication has been built upon complication may be easily grasped by observing the successive stages of art for which organization had to be provided. At first it had only to serve for a single melodic line; then, in the period of ecclesiastical choral music, for two or more combined melodic lines; then composers combined more and more melodic lines as they found out how it could be done, and this caused their minds to be almost monopolized by what may be called linear organization, which is a systematized relation of melodic parts which are quasi independent, but knit into unity by their subjection to the rules of melodic scales, which were called modes. The highest outcome of long and concentrated thought in this direction was the type of organization known as the fugue, which is a linear principle of organization vitalized by the systematic distribution of recognizable melodic phrases. Fugue was the first form in which the musical idea was the most prominent factor in organization, and in the hands of genuine composers was developed to a high degree of perfection. But it left almost unrealized the problem of organization which dawned upon men’s minds as necessary when they began to feel the harmonies which were the result of combined melodious parts as entities in themselves. This problem was dealt with in the period when men devoted themselves to the classification of harmonies in key systems, which gave every harmony a definite function in artistic organization; and the capacity of the human mind was developed till it could recognize one succession of harmonies as representing one key centre and another succession