XI. Chord Families and Diatonic Substitution
Progressions strongly tend to move from the tonic family to the subdominant
family, then to the dominant family, and then back to the tonic family.
Tonic Family
I iii vi
Subdominant Family
ii IV vi
Dominant Family
V vii
The vi chord may function as either tonic or subdominant depending on its
place in the progression. In minor keys the bVI chord is always in the subdominant
family.
Chords in the same family may be substituted for each other for variety. In
the example below, a Dm chord may be used in place of F major in bar 2.
C | F |G | C |
Substitutes may be played in addition to the basic harmony to increase the
sense of movement.
C Am |F Dm |G Bm7b5 |C |