In their exploration of the possibilities of melodic combinations, Okeghem, Des Prés, and their successors laid down the primary laws of music and consequently established the first forms, for in music form is the first manifestation of law. The first of all musical forms was that found in the songs of the people in which the rhythmic dependence of the music upon the text was the controlling principle. But the earliest scientific composers, the monks and church writers, having only the liturgy in mind, ignored the folk songs and so robbed themselves of the aid of the simple rhythmic forms dependent upon verse. They naturally could not avail themselves of these forms because the liturgy was not written in verse. Having, therefore, nothing to serve as a model, they were obliged to start from the foundation and build a wholly new musical system. Thus they produced, in a series of developments occupying nearly 700 years, the most closely knit and purely intellectual group of musical forms, those classed as canonic or fugal. Hence we find that the first of the three great periods of musical history, the Polyphonic, is chiefly distinguished by intellectual characteristics, because, as I have said, the evolution of form is in the main an intellectual process. But even the canonic forms were modified by the irrepressible spirit of romanticism. Whenever in the history of music the desire to express one's self has acted upon a man of original mind it has caused a change in forms. The first period of the Netherlands school, for example, was devoted to the formulation of musical science. In the second period came Josquin des Prés, whose desire for pure beauty in music led him to modify the forms left him by Okeghem. In the third period, as we have seen, Willaert and others still further modified forms and introduced the element of tone-painting. In the fourth period we find Lasso again modifying forms and introducing the element of pure emotional expression, which, in so far as unaccompanied church music is concerned, was perfected by his great contemporary, Palestrina. In later periods we find that Haydn laid the foundations of the sonata, Mozart of the concerto and genuine opera, Beethoven changed the whole trend and scope of the symphony, Chopin, Schumann and Liszt remodelled the diction and the technics of the piano, and Wagner produced an absolutely new operatic form. These are only a few instances. This book is made up of the accounts of these and others.