For most of the twentieth century, opera singers were not beholden to the ideal physical standard of women dictated by popular culture, but rather focused on serving the music and perfecting their artistry. Unprecedented sociocultural changes throughout the twentieth century exposed the shifting ideals of each generation and how they were promoted through mass media and advertising. This thesis surveys the time period of the 1890s to the present day for the purpose of analyzing cultural trends, philosophies and technologies that shaped the century. Societal pressure to make the body a project and the focus of one's own intense attention now reflects back onto the opera stage where audience members expect to see what society has dictated to be an acceptable female form. Artistic and stage directors are influenced by society's decree that only thin is beautiful, imbedding into the mindset of the art form notions that now affect how female professional opera singers are depicted and even employed.

This dissertation investigates how W. A. Mozart applies the concept of key characteristics—the affective properties of each tonality—as discussed by three of his contemporaries, Johann Mattheson, C.F.D. Schubart and G.J. Vogler, to four soubrette and four prima donna characters from four of his late Italian operas: La Contessa and Susanna in Le nozze di Figaro; Donna Anna and Zerlina in Don Giovanni; Fiordiligi and Despina in Così fan tutte; Vitellia and Servilia in La clemenza di Tito. The analytical method of this dissertation provides a hermeneutical tool to search for meanings in Mozart's music. The application compares the libretto text and its corresponding tonal center with the description of key characteristics on a micro level, to reveal significant dramatic and practical implications from Mozart's key usage in his operas.