The harmonic rhythm, or the pace at which the chords occur, may be varied including two beats (half-measure) per chord, four (full measure or bar), eight (two measures), and eight beats per chord except for IV and V (7) which get four each. This is also similar to the I–V–vi–IV progression. Variations include switching the vi and the IV chord to create I–IV–vi–V, as is used in ' More Than a Feeling' by Boston and ' She Drives Me Crazy' by Fine Young Cannibals. A very common variation is having ii substitute for the subdominant, IV, creating the progression I–vi–ii–V (a variant of the circle progression) and thus the ii–V–I turnaround. The vi chord before the IV chord in this progression (creating I–vi–IV–V–I) is used as a means to prolong the tonic chord, as the vi or submediant chord is commonly used as a substitute for the tonic chord, and to ease the voice leading of the bass line: in a I–vi–IV–V–I progression (without any chordal inversions) the bass voice descends in major or minor thirds from the I chord to the vi chord to the IV chord.Īs with any other chord progression, there are many possible variations, for example turning the dominant or V into a V 7, or repeated I–vi progression followed by a single IV–V progression. In this case, the 50s progression uses a IV chord, resulting in the ubiquitous I–IV–V–I progression. However, since a I–V–I progression is repetitive and skips most of the circle of fifths, it is common practice to precede the dominant chord with a suitable predominant chord, such as a IV chord or a ii chord (in major), in order to maintain interest. This particular cadence, V–I, is known as an authentic cadence.

The most conclusive and resolving cadences return to the tonic or I chord following the circle of fifths, the most suitable chord to precede the I chord is a V chord. The destination of a chord progression is known as a cadence, or two chords that signify the end or prolongation of a musical phrase. In Western classical music during the common practice period, chord progressions are used to structure a musical composition.

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