chord-scale system
The chord-scale system is a method of matching, from a list of possible chords, a list of possible scales. The system has been widely used since the 1970s and is "generally accepted in the jazz world today". However, the majority of older players used the chord tone/chord arpeggio method. The system is an example of the difference between the treatment of dissonance in jazz and classical harmony: "Classical treats all notes that don't belong to the chord...as potential dissonances to be resolved...Non-classical harmony just tells you which note in the scale to potentially avoid..., meaning that all the others are okay". The chord-scale system may be compared with other common methods of improvisation, first, the older traditional chord tone/chord arpeggio method, and where one scale on one Root is used throughout all chords in a progression (for example the blues scale on A for all chords of the blues progression: A7 E7 D7). In contrast, in the chord-scale system, a different scale is used for each chord in the progression (for example Mixolydian scales on A, E, and D for chords A7, E7, and D7, respectively). Improvisation approaches may be mixed, such as using "the blues approach" for a section of a progression and using the chord-scale system for the rest.