Jazzforschung / Jazz Research 32 (2000)

Gerhard Bickl

Chorus und Linie: Zur harmonischen Flexibilität in der Bebopimprovisation



A. Chorus improvisation in Jazz and method of the study

The most important form of improvisation in Jazz is the chorus improvisation, to play a melodic line over a given harmonic-metrical model, the chorus, which consists of a sequence of chords in a fixed form (changes). Bebop, father of all modern jazz styles delivered important impulses to flexibility and independence of the (improvisation) line. He showed ways to play more freely, in a sense being more chromatic, over functional-harmonic arranged chord progressions.


The below mentioned results are based on the analysis of selected improvisations of three prominent musicians of Bebop, Charlie Parker, Dizzy Gillespie, Bud Powell, and here and there of Miles Davis. It is useful to examine, how the musicians harmonically interpreted the same chorus model (theme) while playing solo. The cited models are the chorus forms Blues, Rhythm Changes, Hot House, All the Things You Are and A Night in Tunesia, frequently played in Bebop.


B. The chorus

I. The given elements in the chorus

The melody of a tune can almost completely be excluded as a starting-point for the improvisation, more important are meter, form and especially the chord sequence (changes) and the system of functional harmony behind it respectively.

II. Rules of harmony

The changes of the chorus models are arranged according to functional-harmonic rules. Three aspects form the basis of harmony:


1.       the modalities (scales) major, (extended) minor, and blues (on C: c – d – e – f – g – a – b, c – d – eb – f – g – ab – a – bb – b, c – d – eb – e – f – f# – g – a – bb);

2.       the four-note-chords (seventh chords), which are divided into several categories (chord qualities – major seventh chord (MA7), minor major seventh chord (mMA7), minor seventh chord (m7), half-diminshed minor seventh chord (m7(b5)), dominant seventh chord (7) diminished seventh chord (o));

3.       the hierarchical (functional) order around the central chord, the tonic. At first there are particular chord sequences (cadences), consisting of the tonic and the most important secondary chords (dominant, subdominant of the IVth degree, diminished tonic (Io)) and which then are changed and extended by additional and altered chords (e. g. IMA7 – V7 – IMA7 becomes IMA7 – VI7 – IIm7 – V7 – IMA7).


To change the tonic within a tune (modulation) is a frequent technique of composition. Finally the regular forming of the chord progression (harmonic rhythm) is a typical feature of the changes.


C. The line

I. Harmonic techniques in Bebop improvisation – summary

The harmonic techniques used in the Bebop line are organized as follows (the tones of the (four-note-) basic chords from the changes are denoted as „chord-owned“ or „consonant“ respectively):


1.       use of chord-owned tones only;

2.       non-chord-owned tones or diatonic and chromatic additional tones respectively, which will be resolved;

3.       non-chord-owned tones, which will not be resolved (tensions);

4.       modification of the chord progression by exchanging (substitution), adding (additional chords) and omitting chords or exchange of whole chord groups (horizontal, chord-embracing conception) respectively;

5.       limitation of the harmonic extension by the almost always recognizable harmonic foundation of the changes in the line, so to say, on the one hand a tone row preferring the consonant tones, on the other hand the orientation on the prevailing chords;

6.       the fundamentally existing consideration of harmonic and formal breaks in the succession of phrases.


II. Techniques without changing the basic chord

1.       The exclusive use of the tones of the basic chord is very rare, because it does not correspond with the inclination of Bebop to permanent variation, as it happens in melody and rhythm, too.

2.       The non-chord-owned tones, which will be resolved (passing note, neighbour note etc.) mostly occur alone or in twos. The harmonically most weighty form is the double suspension or indirect resolution (upper and lower neighbour note). All tones of the chromatic scale will be used, for the present permitted by their straight forward aiming at the tones of the basic chord – their diatonic or chromatic origin is secondary.

3.       The non-resolved non-chord-owned tones are the tensions representing a extension in sound or „colouring“ of the chord types without changing them in their essence. The boundary-line to the additional tones is frequently flowing.


The first guide line for the choice of tensions is the cadencial space of a tonic to which the chord is related directly. This leads to a basic material consisting of the major or minor scale of the really appearing or only implicated tonal center. The tensions especially of the dominant seventh chord can be derived – aside from major and minor scale – partly from the functional and tonal (sound) relation to the diminished seventh chord a major third higher and to the dominant seventh chord a tritone away and partly from the likewise as tonic scale used blues scale.


In many cases the musicians have the possibility to attach a chord to different cadencial or functional spaces, the preceding, the following or a superior (e. g. D7 in the 17th bar of the Rhythm Changes (keynote Bb) is III7 in the superior Bb major and V7 to the following G major chord (G7)). Sometimes chords without tonic function can get tonic character for a while. This takes effect on the selection of their tensions and the surrounding chords (e. g. C7, dominant of FmMA7 at the beginning of Hot House (keynote C) can be understood as blues tonic (I7)).


The selection criteria for creating tensions are furthermore the preservation of the characteristic sound of the different chord types and of the chordal unit as quality. This means, for instance, in the case of the dominant seventh chord, that many tensions can be added, because in general they strengthen the chord´s tension function and dissonant sound effect respectively, only the major seventh is avoided, because it cancels the chord quality.


III. Techniques with alteration of the changes by putting in single new chords

1.       Substitution

The possibilities of substitution originate at first sight from the overlapping tones of the chords, their sound relation. The underlying principle, however, is, that there is a change in sound, through varying the root and/or the chord quality, but the fundamental function will be preserved, at best intensified towards the main functions, tonic and dominant, which are again the relevant axis of the Bebop harmonic system. A functional intensification is, for instance, the replacement of a weaker cadencing (resolving) minor seventh chord by a stronger dominant seventh chord with the same root (e. g. II7 – V7 instead of IIm7 – V7). The sound results by substitution are very close to them by tensions. Many examples can be submitted to both categories. Although it is rather rare, the tritone substitution of dominants extended by minor seventh chords is worth mentioning, because it has a sharp and strong sound effect (e. g. bVIm7 – bII7 instead of IIm7 – V7).

As with tensions the ambiguity of the functional position of chords (the possible relation to different tonal centers) supports substitution, particularly the variation of chord quality. Sometimes you can hear a exchange of chords between the three modalities (major, minor, blues) – modal interchange, e. g. IIm7(b5) (from minor) substitutes IIm7 in a major progression. The farest reaching form is the substitution of the central chord, the tonic, in the Blues (IMA7/I7) – occasionally beyond this form; the harmonic core, the major triad, however, remains untouched.


2.       Additional chords

Through additional chords the chord progression of the chorus will not be changed, but supplemented by one chord, seldom by two. This will always be achieved by the direct, so to say functional-harmonic derivation of a chord from a chord of the changes. It is always a resolving or dependent chord, never a tonic chord (e. g. #Io between IMA7 and IIm7). Theoretically there are all chromatic tones available for the Bebop musicians at any time due to the use of secondary dominants. Thus the repertory of possibilities in the line grows considerably.


IV. Horizontal, chord-embracing techniques

In Bebop the higher ranking chords of the changes, as determined by functional harmony, were considered as leading points in horizontal, chord-embracing improvisation, and the space between them will be filled up in different ways, e. g. by reduction to the main chord solely or by putting in another functional chord progression: instead of IMA7 – VIm7 – IIm7 – V7 – IMA7 you hear IMA7 throughout or IMA7-IIm7-Io-IMA7. In general tonic and/or dominant of a closed part are the pivots of horizontal lines. In the Rhythm Changes a similar status like the dominant sometimes does have the subdominant (of the IVth degree) in the sixth bar of the A-section and the diminished seventh chord over the tonic (Io), which comes from a variant of this chorus form, where Io takes the place of V7. These three chords (V7, IVMA7, Io) are the functions next to or immediately beneath the tonic in the hierarchy of a tonality, with whom the tonic forms the three elementary cadences.


The second background of horizontal phrases to recognize is the melodic consistency – a very common factor in the harmonic events, which appears here very clearly. The consistent development of the line is dominant and disregards the given chord progression. Consistent development means, that a concise melodic motif influences the forming of the line for a longer period of time, being repeated in a more or less strong way. Bebop indeed operates reservingly with this concept, there do not arise any chord or sound structures, which would totally leave the given cadencial space and the outgoing only happens over a short distance. That happens mainly in the tonic-dominated, quasi-modal A-Section of the Rhythm Changes.


V. The harmonic rhythm in the line

Another explanation for many events in the line could be that the musicians intentionally shift the harmonic rhythm, that is lengthening or shortening the duration of chords, playing single chords a little earlier or later as given in the changes.


VI. Complete consideration of the consonance-dissonance-relation

Comparing the four-note basic chords and the additional tones, consonant and dissonant, chord-owned and non-chord-owned tones as a whole, a permanent „in-“ and „outgoing“, a going into the chord and out of the chord, in short intervals, emerges. In its density there is a similarity to the later classical European, still functionally-harmonically structured music, but it happens in another way, in the intervallic succession and above all in rhythm and phrasing. Statistically considered in the line the four basic tones nearly always prevail per harmonic unit. Only sporadically more than the half of the chord duration will be occupied by non-chord-owned tones.


VII. Line and harmonic-formal sections and breaks

In Bebop it is a rule to pay attention to the formal sections by setting breaks. This happens according to the principle to change the melodic direction or to interrupt the movement at the transition to the next part. The last two bars of a section and, one could say the first bar of the following part belong to the transition zone. The final bars are occupied by a single chord or function respectively, either by a concluding tonic or by the dominant to the next section. Sometimes the melodic break can be very subtle. The musicians like to finish their solos almost without exception with the end of a chorus model, joining the tonic. Very often they play to the first beat of the next chorus. Besides, the final tone is a tone from the basic chord (consonant).


D. Résumé

Let me summarize the principles of the harmonic flexibility in Bebop improvisation:


-          the permanent, well-organized use of non-chord-owned tones,

-          the extended conception of the chord qualities by tensions,

-          the adjustment to the tonic and the tonic scales (modalities) major, (extended) minor and blues,

-          the interchange between this modalities,

-          the extreme superficial flexibility of the dominant function, beside the tonic the most important function,

-          the relationship, interdependence and functional ambiguity of chords,

-          the subtle variation of harmonic rhythm,

-          the legitimation of greater harmonic discrepancy through melodic consistency,

-          the tendency to use more consonant than dissonant tones,

-          the paying attention to harmonic-formal breaks.


In Bebop the dominant-tonic-principle begins to widen to a general tension-release- or outside-inside-thinking and the horizontal technique of stretching the tonic is a first step to the modal concept of later jazz styles.


The Bebop concept enjoys a high reputation amongst jazz musicians until today, for it looks like an ideal compromise between linear freedom and chorus principle or: like the classical form of the harmonically bound improvisation (chorus improvisation). The Bebop line does not adhere to the chord and does not move around unrestrained in the chromatic space – the feeling of tonality and the harmonic complexity and veiling are in balance.