The Structure and Essence of Jazz

The Structure

Jazz is made by arranging chords, melodies, and rhythms into units called songs.

Chords are note clusters, melodies are note sequences, and rhythms are repeating patterns that make clear the music’s beat.

Usually, the chords, melodies, and rhythms are arranged into two contrasting sections. Combining these contrasting sections into various configurations is what determines a song’s form.

In jazz, songs are typically devised using one of two standard forms: (1) twelve-bar blues or (2) thirty-two-bar pop song (Giddins and DeVeaux 31).

The twelve-bar blues form configures two contrasting lines of poetry into the following order: AAB. Three lines of blues poetry in this arrangement take twelve measures (bars) to transpire, hence the name.

A measure is a sector of music that lasts four beats. Even if you are a non-musician, you can understand the concept of a musical measure by counting to four, repeatedly, in a cycle. If you make the space between each utterance perfectly even, then you’ll succeed in constructing a musical beat, which is the primary impulse of music. Beats are grouped by measures like this: if you count to four twelve times in a row, then you’ll have parsed twelve measures of beats.

The Ma Rainey song, “Booze and Blues” has a typical twelve-bar, AAB format. Each stanza of poetry occupies four measures of music.

  • Went to bed last night and boy I was in my sleep, sleep
  • I went to bed last night and I was in my sleep
  • Woke up this mornin’, the police was shakin’ me

The first two lines are labeled with an A because they’re (essentially) the same, and the third line is labeled with a B because it’s the contrasting follow-up to the first two lines.

In a jazz context, one complete cycle through a song’s form is called a chorus. The lyrics above represent one chorus of the song “Booze and Blues,” and it takes twelve bars to complete this set of words.

The chorus exists upon a musical superstructure provided by harmony. Harmony is comprised of simultaneous note-clusters called chords. Chords function in relation to one another so as to create musical tension and stability. Blues harmony consists of just three chords: the one-chord (I), the four-chord (IV), and the five-chord (V).

The standard blues chord progression is as follows:

  • The I chord comes first and is played for the first four bars.
  • Then, the IV chord is played, and it lasts for two bars—measures five and six.
  • Next, the music returns to the I chord, which sounds for two more bars—measure seven and eight.
  • Lastly, the V chord is played in measure nine, the IV chord is played in measure ten, and the I chord is played in measures eleven and twelve.

The harmony of blues music almost never deviates from this scheme, and its ubiquity is why blues musicians can perform together having never rehearsed a single note.

Depicted below is a typical blues song in the jazz tradition.

Blue Monk
Source: The Real Book. 6th Edition. Hal Leonard, 2004.

During the last two measures of the twelve-bar blues, musicians often play melodic flourishes known as turnarounds. Turnarounds help musicians keep their place within the form by providing an auditory signal to convey the start of a new cycle.

Turnaround Riff 1
Source: Chappell, Jon. Blues Guitar for Dummies. Wiley Publishing, Inc., 2007.

Jazz musicians are famous for choosing their tunes indiscriminately from pop, blues, country, folk, and spirituals. Despite this promiscuous attitude towards tunes, jazz repertoire is especially connected to the tradition of musical theater. During the 1920s and 1930s, jazz musicians began to adopt the thirty-two bar pop song format endorsed by musical theater composers (Szwed chapter 4).

Like blues, the pop song is devised using a binary format. The main difference between blues and pop is that the A and B sections of pop songs are comprised of eight-measure-figures instead of individual lines of poetry. Another difference is that the A section of pop music comes back for a final repeat after the B section. The pop format is AABA and the blues format is AAB (Giddins and Deveaux 32).

Still another difference between blues and pop is one of harmony: The thirty-two-bar pop form employs any configuration of chords; the twelve-bar blues form employs only one configuration of chords.

Often, pop songs display highly complex and refined twists in harmony. Regardless of most pop songs being harmonically unique, some standard chord progressions have evolved. And jazz players and composers have adopted these chord sequences into the tradition as standards.

One of these standard chord progressions is known to players as “Rhythm Changes.” It is derived from the 1930s George and Ira Gershwin song, “I Got Rhythm,” from the theater show, Girl Crazy (Giddins and Deveaux 34).

“Rhythm Changes,” and most other thirty-two bar pop songs, employ the AABA form. Sometimes there is a short (four measure) introduction affixed to the top of the form to allow the dialogue of the film or musical to transition into singing. Not including the intro, the thirty-two bars of the main song repeat in episodes called choruses—just like blues (Giddins and DeVeaux 35).

The process of furnishing an existing chord sequence with a new melody is called contrafact. For example, the chords to Gershwin’s  “I’ve Got Rhythm” were used in a song by Duke Ellington called “Cotton Tail.”

The Essence

The twelve-bar-blues and the thirty-two-bar pop song formats provide foundations that support an essential aspect of jazz: improvisation.

Improvisation, which is the impromptu creation of melodies and rhythms, deserves this notoriety because it allows individual voices to be heard. Because individual voices were the focus of works songs, field hollers, and spirituals (jazz’s ancestral traditions), it is easy to see why improvisation became so essential.

Here’s how it’s done: The improviser takes the musical content from an existing blues or pop song and expands on the ideas therein—usually by varying the melody, inventing new melodies, or both. Since the harmonic understructure of any given blues or pop song proceeds predictably, the improviser can guide his or her musical thoughts based on the structure of the song.

Improvisation as unpremeditated musical creation is mostly a fiction. The song’s musical content informs which notes will sound good, and the musician’s skill set informs which notes will be possible.

If he or she cannot physically play a sequence of notes, then no number of takes will yield that sequence of notes.

In any case, improvisers play in a premeditated way. Usually, an improviser will run through learned sequences that they’ve secured into muscle memory and that they know will work at certain deployment points within a song’s structure.

There are two basic strategies employed by jazz musicians to deploy their licks and phrases on the spur of the moment: (1) modal improvisation and (2) harmonic improvisation.

Modal improvisation is using a scale (which is a set of notes) to produce a melody. Notes outside the scale will often sound “wrong,” so players avoid them. While playing in this way, an improviser may think to herself, “these notes in this scale here are all okay to use, so I can just play any of them in any order I want.”

This diagram is from my unpublished book about scales. It depicts two octaves of the C Major Scale.

The player’s only task, then, is to devise a rhythm in which to frame the legal notes. Improvised rhythms are often derived from the rhythm of the song’s melody.   

Modal playing works great for the blues because blues music is extremely limited harmonically. (Blues only has three chords.) The pitch set players use to improvise in this context is called the Blues Scale. There are two varieties of Blues Scale: one major and one minor. The major variety is sometimes called the Bluegrass Scale.

C minor Blues
The C Minor Blues Scale features an F and an F-sharp. The F-sharp is the “blue” note.
G-form bluegrass
The C Major Blues Scale features an E-flat and an E. The E-flat is the “blue” note.

Modal playing won’t work for the thirty-two-bar pop song because the underlying harmony of that style is too complex. Since no single scale will cover all the changes involved in a thirty-two-bar pop song, players must do their impromptu playing using harmonic improvisation.

Harmonic improvisation is the act of using the notes of the individual chord to inform all decisions about which notes to use. It is one of the most difficult tasks in the whole artform because the chords are often flying by at full tilt—that is, chords often last for only a second or two before moving on to another chord.  

A good analogy to harmonic improvisation is skeet shooting. The skeet shooter must identify, aim, and shoot each flying target before the next one flies into view. Jazz players are, in this sense, blowing each chord apart as they arrive, exist, and pass away. For every moment of harmonic improvisation, players must be aware of which chord the band is on and which chord the band is going to next.

Both strategies of improvisation—harmonic and modal—dispel the notion of improvisation as being completely unpremeditated. The foreknowledge that guide improvisers the most include the song’s key (scale), chord sequence, and head melody.

If players know these three things, then improvisation may become an episode of pure expression—that is, one in which licks and phrases are being born of unconscious thoughts.

Here there is a link between determinist philosophy and improvisation: Musicians often realize musical ideas on their instruments before they are consciously aware of their content.


Jazz is an individual’s art form, and improvisation is a way for an individual to converse with the tradition. The resulting discourse is the point of the whole genre.

Most of the jazz tradition is carried on by players being familiar with the accepted-by-tradition repertoire. Hundreds of jazz songs exist within this tradition, and the responsibility of jazz musicians is to be familiar with as many of these “standards” as possible.

A helpful anthology of jazz standards evolved in the 1970s called the Fake Book. It was in violation of many copyright laws, so it was illegal.  But the Fake Book was eventually standardized and published legally as the Real Book by Hal Leonard Publishing in 2004 (“Real Book” para 1).

The Real Book has over four hundred jazz standards contained within a single volume. It’s akin to a jazz player’s bible. To jazz musicians, this book possesses the shape, structure, and essence of the art form.

Works Cited

Giddins, G., & DeVeaux, S. Jazz. New York: W.W. Norton and Company, 2009. 

“Real Book.” The Free Encyclopedia. Wikimedia Foundation, Inc. 8  July 2016.

Szwed, J. F. Jazz 101: A Complete Guide to Learning and Loving Jazz. Narr. by Grover Gardner. Blackstone audio, Inc., 2000.

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