Functional & Non-Functional Harmony in Improvisational Practice

Many jazz musicians learn to improvise through an understanding of chord-scale correspondence whereby note choices are made according to the function of a chord in a progression. For example, Dorian is an appropriate scale choice for improvisation during a chord functioning as ii in a ii-V progression; Mixolydian is an appropriate scale choice for improvisation during the V chord. One of the most important aspects of chord-scale correspondence is that it requires recognition of the function of a chord in its surroundings: a Dorian scale is not necessarily appropriate for every minor seventh chord that comes along (other scale choices for such a sonority possibly including Phrygian, Aeolian, and Locrian); but it is appropriate for the minor seventh chord that functions as ii. Understanding of function and assessment of context provides perspective in making a choice between scale resources.
Training in functional harmony also heightens an improviser's awareness of compelling voice-leading. Sensitivity is sharpened regarding the tendency of certain scale degrees to move to certain other degrees: for example, scale-degree 4 as the seventh of a dominant seventh chord has the tendency to resolve down by step to scale-degree 3, the third of the tonic chord. Concern for voice-leading also encompasses the idea of avoiding certain pitches either to heighten their impact when they make an appearance in the following chord (for example, avoidance of the 13th on the ii chord in a ii-V progression because it is the important 3rd of the following V chord) or to lessen conflict with pitches more important to the structure and function of the chord (such as avoidance of the diatonic fa during the major tonic chord so that it does not divert attention from the more important chord members, mi and sol).
With non-functional harmony, traditional voice-leading concerns are diminished. Non-functional harmony frequently involves a feeling of stasis, a suspension of the sense of progression, and a freedom from the relatively prescriptive tendencies inherent in tonal relationships. Although chord structures are generally familiar ones (tertian chords such as major-minor-seventh, major-major-seventh, minor-minor-seventh, or the like) and the familiar scale choices are available, there is greater freedom in the meaning that is conveyed by the placement of harmonies in a succession of chords. With greater freedom comes greater responsibility: the improviser must invent new means of coherence and musical logic-and new ways to create a sense of forward drive (if desired) and shape to the solo (perhaps depending more on such devices as motivic development or rhythmic treatment). The composer may create new associations (melodic and rhythmic, as well as harmonic) that convey a sense of tension and release and participate in generating the composition's phrasing and form. It is up to the improviser to observe and make use of such new relationships unique to the individual composition.
Thus although it may be easy (from the standpoint of maneuvering through chord changes) to start improvisers with such tunes as So What by Miles Davis where only one scale type, transposed to one additional pitch level, may be required (providing a young soloist freedom from the constant mental calculations required when learning to play the changes of, for example, harmonically dense, up-tempo bebop tunes), great challenges exist in the performance of compositions with non-functional harmony because non-functional harmony removes the pre-existent reason for an appearance of a certain chord at a certain time. This provides an excellent forum for teaching students not only about the function of non-functional harmony but also about the importance of attention to rhythm, ensemble interaction, and listening to and developing one's own ideas in the solo. Non-functional harmonic succession, particularly when combined with a slow harmonic rhythm as generally found in modal jazz, demands much of the performer in the creation of imaginative and compelling musical ideas and the ability to sustain a level of inventiveness and expressiveness through an entire solo.
Improvisers must be aware of the role of both functional harmony and non-functional harmony. Awareness of the reason for a chord's existence will inform an improviser's choices and will deepen his or her understanding of the compositional relationships upon which the improvisation is based.