Generally, successive chords in a chord progression share some notes, which provides harmonic and linear (voice leading) continuity to a passage. In the common-practice period, chord progressions are usually associated with a scale and the notes of each chord are usually taken from that scale (or its modally-mixed universe).
Shorter common progressions may be derived from selecting certain specific chords from the series completing a circle from the tonic through all seven diatonic chords: I-IV-viio-iii-vi-ii-V-I (in major) such as I- V-I = I-V-I I-IV- V-I = I-IV-V-I
The most common chord progressions, in the common practice period and in popular music, are based on the first, fourth, and fifth scale degrees (tonic, subdominant and dominant); see three chord song, eight bar blues, and twelve bar blues. The chord based on the second scale degree is used in the most common chord progression in Jazz harmony, ii-V-I turnaround.
According to Tom Sutcliffe:
Sutcliffe’s thesis is that major chord combinations, such as I-III-IV-V-VII, cannot be explained in pure modal terms; in this combination, they do not exist in the usual modes and must be explained as a new harmonic system combining elements from the blues and elements from modality.
from Ottman (1997). Elementary Harmony.
Major/minor
Blues-Modal
Mixed
Other
The original progression may be notated as follows (typical 12-bar blues):
1 2 3 4 5 6 7 8 9 10 11 12
I/ I/ I/ I// IV/IV/ I/ I// V/ IV/ I/ IWhere the numbers on the top line indicate each bar, one slash indicating a bar line and two indicating a phrase marking, and the Roman numerals indicating the chord function. Important transformations include
1 2 3 4 5 6 7 8 9 10 11 12
I/IV/I/I7//IV/VII7/III7/VI7//II7/V7/I/I//
...7 8 9......III7/III7/II7...
Sequences by fourth, rather than fifth, include Jimi Hendrix's version of "Hey Joe" and Deep Purple's "Hush":
1 2 3 4 5 6 7 8 9 10 11 12
♭VI, ♭III/♭VII, IV/I/I//♭VI, ♭III/♭VII, IV/I/I//♭VI, ♭III/♭VII, IV/I/I//These often result in Aeolian harmony and lack perfect cadences (V-I). Middleton (1990, p.198) suggests that both modal and fourth-oriented structures, rather than being "distortions or surface transformations of Schenker's favoured V-I kernel, are more likely branches of a deeper principle, that of tonic/not-tonic differentiation."
For the ♭ notation, see Borrowed chord.
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