Few terms in music theory are more profound and more enigmatic than ‘tonality.’ First coined by Alexandre-Étienne Choron in his “Sommaire de l’histoire de la musique” (1810), it was popularized by François-Joseph Fétis in the 1830s and 1840s and has subsequently remained an essential part of theoretical discourse. Choron originally used the term to denote music in which notes are related functionally to a particular tonic, the tonic triad. This particular brand of tonality is often known as ‘functional tonality’ and is characteristic of works written by composers such as Handel, J. S. Bach, Scarlatti, C. P. E. Bach, Haydn, Mozart, Beethoven, Schubert, Schumann, Mendelssohn, Chopin, and Brahms. But, as Choron's term has gained currency, so it has expanded its meaning considerably. Nowadays, the term is often used in a very general sense to denote any music that focuses melodically and/or harmonically on some stable pitch or tonic. This definition covers a broad range of music from many cultures and many time periods, from Medieval plain chant to various twentieth-century idioms.

Of the many attempts to explain the nature of functional tonality, perhaps the most comprehensive was undertaken by Heinrich Schenker (1868–1935). In his monumental triptych, Neue musikalischen Theorien und Phantasien, he systematically investigated the ways in which lines and chords behave in functional tonal contexts. In the first volume, Harmonielehre (1906), he explained how functional harmonies (or Stufen) are organized into progressions (or Stufengang). In the second volume, Kontrapunkt (1910, 1922), he explained the basic properties of tonal voice leading (or Stimmführung). And in the final volume, Der freie Satz (1935), Schenker showed how the principles outlined in the Harmonielehre and Kontrapunkt operate recursively across entire monotonal compositions.

But what sorts of relationships did Schenker count as tonal or, to be more precise, functionally monotonal? Why do these relationships work in some ways and not others? Why should we prefer Schenker's theory of functional monotonality to its competitors? The purpose of this book is to try to answer these questions. The Introduction explores some of the general methodological issues that arise when we try to build, test, and evaluate a plausible theory of tonality.