The ‘chord / scale relationship’ is used to identify scales or modes that can be used to improvise, or create melodies, over a chord or chord progression.
When a chord progression is comprised entirely of chords that naturally occur (diatonic) in a key, the scale of that key can be used to improvise over it.
For example, this is a chord progression in the key of ‘C Major’:
|| C | Am | F | G7 ||
So, the ‘C’ Major scale or its relative minor scales could be used to improvise over it.
However, some chord progressions contain chords that do not have a scale in common. So, different scales need to be found for each chord.
Any scale may be used to play over a chord so long as it shares the same quality as the chord and its tonic note (first note) is the same as the root note of the chord.
For example, The ‘A’ major scale could be used over an ‘A’ major chord.
Because the tonic of the scale and root note of the chord are the same (‘A’) and because the quality (major) of both the scale and the chord is the same.
Chords and scales can be broadly categorised into five qualities:
MAJOR, MINOR, DOMINANT, DIMINISHED or AUGMENTED
Below, are examples of scales and modes listed according to their quality.
MAJOR
Major Scale (Ionian Mode), Lydian Mode, Pentatonic Major Scale
MINOR
Natural Minor Scale, Dorian Mode, Phrygian Mode, Pentatonic Minor Scale, Blues Scale
DOMINANT
Mixolydian Mode
DIMINISHED
Locrian Mode, Diminished Scale
AUGMENTED
Whole-Tone Scale
Remember that the scale or mode must share the same quality as the chord and its tonic note must be the same as the root note of the chord.
For example, the ‘G Mixolydian’ mode could be used to improvise over a ‘G7’ chord because they both share the same quality (dominant) and the tonic note of the mode and the root note of the chord are the same (‘G’).
© Carlos Thrale 2014
