Musical Structures and Harmony: Jazz Forms and Secondary Dominance

The 32-Bar AABA Form in Jazz and Broadway

Many jazz standards and popular Broadway show tunes are written in a specific 32-part form known as $AABA$. This structure is essential for musicians to articulate and understand. In this form, the "A" section consists of $8$ bars. This section repeats, resulting in the first $16$ bars ($A$ and $A$). The "B" section, often referred to as the bridge, also consists of $8$ bars. Finally, there is a repetition of the "A" section for another $8$ bars, totaling $32$ bars. This division is fundamental to two of the most important forms in jazz: rhythm changes and the blues.

Historical Roots and the Evolution of the Blues

The history of jazz and contemporary popular music reveals that almost everything we know today evolved from the blues. The blues were introduced by displaced West Africans who were forcibly transplanted from their homes and brought to the New World as slaves. Despite being forbidden from playing their traditional instruments, they adapted their culture and music to their new environment. This musical evolution was a form of adaptation to a new and difficult situation.

Fundamental elements of African music remain deeply embedded in blues and jazz, most notably call and response. Academically, these are referred to as antiphonal exchanges. Similar concepts appear in classical music, such as the question and answer aspect of a phrase, known as antecedent and consequent phrasing. These African musical elements were transplanted into the blues and eventually became the foundation of jazz.

Anatomy of Rhythm Changes

Rhythm changes is a structure that permeates contemporary music in various forms, from George Gershwin's I Got Rhythm to the pop songs of Billie Eilish. While not always appearing in the ideal $32$-bar structure, elements of it are omnipresent. For instance, much of the pop music from the $1950$s and $1960$s utilized only the "A" section, specifically the $1-6-2-5$ progression ($I-vi-ii-V$).

To construct a rhythm changes form from scratch on a blank manuscript, one must account for $32$ bars. The basic structure involves a major cell where there are two beats per chord, meaning two chords per bar. These chords sit on specific beats: beats $1$ and $3$. The progression is $1-6-2-5$. In a standard $8$-bar "A" section, bars $7$ and $8$ typically feature a turnaround progression. A turnaround turns the harmonic progression back to the top or the repeat. In this context, the turnaround in the last two bars is a $1-5-1$ ($I-V-I$) progression.

The Bridge and Secondary Dominance

The "B" section, or the bridge, is also $8$ bars long. It is typically composed of chords $3$, $6$, $2$, and $5$. In rhythm changes, these are often played as dominant chords. For example, in the key of $G$, the bridge would consist of $G^7$ for two bars, $C^7$ for two bars, and $F^7$ for two bars. However, to follow the three-six-two-five cycle properly in $G$, the progression would be $B^7$ for two bars, $E^7$ for two bars, $A^7$ for two bars, and $D^7$ for two bars.

Secondary dominance is a concept used to create stronger tension and resolution. While the diatonic chords in the key of $G$ for these positions would be $B$ minor ($iii$), $E$ minor ($vi$), and $A$ minor ($ii$), they are often changed to dominant chords ($B^7$, $E^7$, $A^7$). This is done through a process called back cycling, which works on targets. The goal is to reach the $5$ chord ($V$) or the $1$ chord ($I$) using the strongest possible cadence: the perfect cadence ($5 \rightarrow 1$).

Tension, Release, and Tonicization

All music can be described as a balance between tension and release. The perfect cadence ($V \rightarrow 1$) is considered the "full stop" in music, whereas an interrupted cadence is like a "comma." Humans are culturally conditioned to expect and desire the resolution of a $5$ chord to a $1$ chord. Composers often play with this expectation by delaying or surprising the listener with the resolution.

Temporary tonicization is a principle where a chord other than the actual tonic is treated as a temporary tonic for a brief period. If the goal is to reach $D^7$ (the $5$ chord in the key of $G$), the composer looks for the strongest cadence to approach $D$. Since a perfect cadence is $5 \rightarrow 1$, the composer uses the $5$ of $D$, which is $A^7$. Thus, $A^7$ is the secondary dominant, or the $5$ of $5$. This back cycling continues: the $5$ of $A$ is $E^7$, and the $5$ of $E$ is $B^7$. These are written as $\frac{V^7}{I}$, $\frac{V^7}{V}$, or $\frac{V^7}{ii}$.

Practical Improvisation and Modal Changes

For a jazz musician, prowess is defined by the ability to play the blues or rhythm changes in any key. There are hundreds of "standards" based on these forms. As musicians learn more advanced concepts, they realize that music is based on a few recurring principles rather than an overwhelming amount of micro-details.

Improvisation in jazz occurs not just in soloing but also harmonically. In an ensemble, a pianist might decide to use secondary dominants ($5$ of $5$) in real-time. This changes the modal structure for the soloist. For example, in the key of $G$, the $6$ chord is $E$ minor. Diatonically, this would call for the $E$ Aeolian mode. However, if the chord is changed to a dominant $E^7$, the soloist must switch to the $E$ Mixolydian mode.

When analyzing chords, it is most effective to look at intervals from the root rather than intervals between consecutive notes. A dominant $7$th chord is defined by a major third, a perfect fifth, and a minor seventh from the root. This is distinct from a major $7$th chord, which has a major seventh interval.

Questions & Discussion

Question: Regarding Roman numeral notation, do you still say two minor seven ($ii^7$) even if it is a dominant $A$ chord, or do you say five seven of two ($V^7/ii$)?

Answer: It is more correct to use $\frac{V^7}{ii^7}$ (five seven of two seven). Specifically, if the goal is to reach a dominant $5$ chord, the preceding chord would be $\frac{V^7}{V^7}$. For the purpose of explaining the transition from diatonic chords, one might start with the minor designations, but once the chord is changed to a dominant, the functional notation is $V^7$ of the target chord.

Question: Why is it a major third in the dominant chord?

Answer: In a dominant $7$th chord, the intervals are a major third ($1 \rightarrow 3$), a perfect fifth ($1 \rightarrow 5$), and a minor seventh ($1 \rightarrow 7$). For instance, in $G$, the notes would be $G$, $B$ (major third), $D$ (perfect fifth), and $F$ natural (minor seventh). Looking at the relationship from the root is a much better system than trying to calculate the distance between each individual note in the stack.