For many composers, elements of symphonic form, from the classical period to the end of the romantic era, have remained relatively static. While certain conventions, such as the substitution of a scherzo for a minuet and trio, have changed from time to time, the classical symphonic form is thought to have been used unchanged or in minute variation. However, the progressive twentieth century symphonist, who has espoused both traditional form and progressive harmonic and melodic ideas, has encountered an interesting problem, which begs the question of how to preserve a form largely based on harmonic movement (or 'progression" and 'development") or thematic contrast in a progressive harmonic idiom. This question is particularly pertinent with the use of sonata-allegro form, in which certain harmonic tendencies have been paramount and a particular balance of tension and release is usually preferred. Techniques such as continuous variations, ostinati, non – periodic melodies, and baroque rhythmic regularity, as well as new harmonic and other organizational practices such as pandiatonicism, free atonality, 12 – Tone method, klangfarbenmelodie, and numerous 'atonal" practices from impressionism to pointillism, can be viewed as a disruption of the symphonic form in the 'traditional" sense. Many composers have adapted the symphony to these progressive idioms, and have provided various solutions to those who might wish to continue the development of the symphony based upon the examples of romantic symphonists such as Beethoven and Brahms. The symphonic form has been reinterpreted to fit the needs of the modern composers, who were never inclined to let music theorists confine them to the antiquated examples of days past. The conventions of pandiatonicism and 12 – Tone composition in the twentieth century symphony will be discussed through the symphonies of composers who favor the previously mentioned harmonic techniques, Ellen Zwilich and Anton Webern.