ii–V–I progression

With the addition of chord alterations, substitutions, and extensions, limitless variations exist on this simple formula.

The ii–V–I progression is "a staple of virtually every type of [Western] popular music", including jazz, R&B, pop, rock, and country.

They serve two primary functions, which are often intertwined: to temporarily imply passing tonalities and to lead strongly toward a goal (the "I" chord).

In bar 4, instead of the simple V–I root motion in the original blues, the ii chord of the B♭7 (Cm) is included so that the measure is even more directed toward the following downbeat with the B♭7.

For example, in the key of C, the standard jazz ii–V–I progression is Dm7–G7–Cmaj7, and the thirds and sevenths of these chords are F–C, B–F, E–B; inverted for smoother voice leading, these become F–C, F–B, E–B.

Four-voice classical, three-voice and four-voice jazz "versions" [voicings] of the ii–V 7 –I progression. The classical example features inversions to emphasize the bass line's independence while the jazz examples feature root progression by fifths and "perfectly smooth voice leading" produced by the 7th of each chord falling a semitone to become the 3rd while the 3rd becomes the 7th of that chord. [ 4 ]
ii–V–I
ii–V–I