See also: Functional harmony and Voice leading
The harmonic language of this period is known as "common-practice tonality", or sometimes the "tonal system" (though whether tonality implies common-practice idioms is a question of debate). Common-practice tonality represents a union between harmonic function and counterpoint. In other words, individual melodic lines, when taken together, express harmonic unity and goal-oriented progression. In tonal music, each tone in the diatonic scale functions according to its relationship to the tonic (the fundamental pitch of the scale). While diatonicism forms the basis for the tonal system, the system can withstand considerable chromatic alteration without losing its tonal identity.
Throughout the common-practice period, certain harmonic patterns span styles, composers, regions, and epochs. Johann Sebastian Bach and Richard Strauss, for instance, may both write passages that can be analysed according to the progression I-ii-V-I, despite vast differences in style and context. Such harmonic conventions can be distilled into the familiar chord progressions with which musicians analyse and compose tonal music.
Various popular idioms of the twentieth century differ from the standardized chord progressions of the common-practice period. While these later styles incorporate many elements of the tonal vocabulary (such as major and minor chords), the function of these elements is not identical to classical models of counterpoint and harmonic function. For example, in common-practice harmony, a major triad built on the fifth degree of the scale (V) is unlikely to progress directly to a root position triad built on the fourth degree of the scale (IV), but the reverse of this progression (IV–V) is quite common. By contrast, the V–IV progression is readily acceptable by many other standards; for example, this transition is essential to the "shuffle" blues progression's last line (V–IV–I–I), which has become the orthodox ending for blues progressions at the expense of the original last line (V–V–I–I).1
Coordination of the various parts of a piece of music through an externalized metre is a deeply rooted aspect of common-practice music. Rhythmically, common practice metric structures generally include:2
Durational patterns typically include:3
Patterns of pitch and duration are of primary importance in common practice melody, while tone quality is of secondary importance. Durations recur and are often periodic; pitches are generally diatonic.4
(Tanner & Gerow 1984, 37) - Tanner, Paul, and Maurice Gerow (1984). A Study of Jazz. Dubuque, Iowa: William C. Brown Publishers. Cited in Robert M. Baker, "A Brief History of the Blues". TheBlueHighway.com. https://web.archive.org/web/20090629213200/http://thebluehighway.com/history.html ↩
(Winold 1975, chapter 3) - Winold, Allen (1975). "Rhythm in Twentieth-Century Music". In Aspects of Twentieth-Century Music, edited by Richard Peter Delone and Gary Wittlich, Englewood Cliffs, New Jersey: Prentice-Hall. ISBN 978-0-13-049346-0. pp. 208-269. ↩
(Kliewer 1975, chapter 4) - Kliewer, Vernon (1975). "Melody: Linear Aspects of Twentieth-Century Music". In Aspects of Twentieth-Century Music, edited by Gary Wittlich, pp. 270–301. Englewood Cliffs, New Jersey: Prentice-Hall. ISBN 0-13-049346-5. ↩