Editing Common practice period (section)

===Harmony===
{{See also|Functional harmony|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 progression]]s 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 chord|major triad]] built on the fifth [[degree (music)|degree]] of the scale (V) is unlikely to progress directly to a [[root (chord)|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 [[Blues|"shuffle" blues]] progression's last line (V–IV–I–I), which has become the orthodox ending for [[Twelve-bar blues|blues progressions]] at the expense of the original last line (V–V–I–I).<ref>{{harv|Tanner & Gerow|1984|loc=37}}</ref>