As compositional style develops from tonal to atonal and twelvetone compositions, the function of music changes from denoting the content of text to embodying its ideas. The text-music relationship no longer determines style, but it expresses the idea of a work. The thesis proposes that the move towards the expressive autonomy of music in opera is possible only with the development of atonality and dodecaphony. Three operas, representing the dominant compositional styles of the time, illustrate these developments: Richard Strauss'
Die Ägyptische Helena, Alban Berg's
Wozzeck and Arnold Schoenberg's
Von heute auf morgen.