Chord Substitution - Extended Chords
Most music doesn't stick to the basic triads. Instead, more complex chords are often substituted for these simple ones. The result is that a great deal of music includes quadrants (four note chords) or other compound chords.
The most natural way to build chords is to add to them in thirds based on the scale of the key in which the chord is occurring. This might be a bit too much to digest at one reading, so let's look at some examples in the key of C major.
In the above, (building the chords from the root note up) we've added one more note to each triad in the key of C major to produce a quadrant. (Note that the symbol Ø means half diminished which is the same as m7♭5.)
Because these chords are formed by adding only one extra note from the C major scale, they form natural chord substitutes. They are all diatonic chords.
For instance, Cmaj7 makes a good substitute for C major, as in the following progression (C6 is also a good substitute as we'll see in the next lesson):
|C / / / |Cmaj7 / / / |C6 / / / |Cmaj7 / / / |
That's a bit more interesting than playing four bars of C. Or Am7 could substitute for A minor as in the following two progressions:
|Am / / / |Am7 / / / |Am6 / / / |Am7 / / / |
|Am / / / |AmM7 / / / |Am7 / / / |AmM7 / / / |
Usually, the diminished seventh chord (a chromatic chord) is substituted for the diminished rather than the half diminished.
If we add only diatonic notes to ii, iii, and vi, notice that all these minors become minor sevenths. This means that most times, if a piece of music has minor chords, you can substitute minor sevenths in their place.
If the supertonic, mediant or submediant chords are chromatic major chords, they can usually be treated as sevenths. For instance, in the key of C major, D major, E major and A major chords could all become sevenths, i.e. D7, E7 and A7.
However, I and IV become major seventh chords, while V becomes a seventh. This means that when substituting for a major chord you would generally need to know whether it was a I, IV or V chord.
One common exception is, if you want a blues/rock feel, you might substitute all sevenths for the majors whatever their scale degree.
Now read: Chord Substitution - Extended Chords 2Understanding Scales | Understanding Chord Structure | Understanding Diatonic Chords | Understanding Minor Scales | Diatonic Chords in Minor Keys | Scale Degree Names | Chord Substitution - Extended Chords | Chord Substitution - Overlapping Chords | Improvisation - Arpeggios | Improvisation - Major Scales | Improvisation - Pentatonic Scales | Improvisation - Blues Scales