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1
Jazz Theory and Practice
Module 5 a, b, c
Dim. 7th & 9th Chords; Extensions to the 13th;
Other Harmonic Structures
B. Extensions: 9th, 11th and 13th chords
Jazz Theory and Practice
Harmonic extensions are notes added to the chord in the second octave
beyond the 7th. In our study of jazz harmony we can easily find labels
for all of these chords with added extensions, but in common
performance practice among jazz musicians there are often wide-ranging
differences between the theoretical chord definition, and the actual chord
that emerges in performance (written or improvised):
� In the large repertoire of sheet music and lead sheets the harmony is
typically from our previous study: almost entirely added-6th and 7th
chords. Many melodic lines, however, contain implied extensions. To
keep the notation simple a basic dominant-7th chord might be
suggested, but certain notes in the melody, especially notes of longer
duration or on a strong beat will become extensions. Over a C7
chord, for example, a D becomes a 9th, or an A becomes a 13th. (but
not an added-6th if the 7th is present!)
� Many performers will routinely add extensions to 7th chords whether
they are notated or not. This happens not only with the “harmony
providers” (keyboard or guitar), but good horn players will include
extensions within improvisations. The practice varies widely
according to style and taste, but extensions to the V7 chord (9, b9,
#9, 13) are very common, and a final I chord is often decorated with
virtually any combination of extensions. This practice is so
widespread that many arrangers assume that the performer will add to
the harmony; another practiced freedom in jazz interpretation!
� Although it would seem that the practice of extensions is about adding
notes to the chord, in fact subtracting notes is almost more important.
� ©2016 Peter J. Clements
2
The subtraction happens in two ways: (1) often during performance
some notated extensions are omitted for practical reasons, and (2) an
extended chord is almost never “complete”: a 13th chord theoretically
contains 7 different notes, but in practice 5, 4, and even 3-note
voicings are typical. The voicing of extended chords is an essential
skill for a good jazz performer, especially pianists, guitarists, and
arrangers.
The 9th, 11th, and 13th are all extensions, and are often regarded as the
outer limits of the jazz harmonic language, at least for chords built of
thirds. This is tertian harmony; there are other basic harmonic
structures used in jazz (especially quartal harmony: chords built of 4ths).
Notice, in the following example, that once the 13th is added to the chord
all seven notes of the scale are represented. The next added third
beyond the 13th is the 15th, which is the root, so isn’t really an added note
at all; there is no 15th chord!
5b1
This example shows extensions to both the major 7th and the dominant
7th chords, and how they are identified. The 11th chord has been omitted:
with a major triad on the bottom the 11th is almost never used, because
the major 3rd combined with the 11th produces a strongly dissonant minor
9th interval. In both 13th chords shown the 11th would almost always be
omitted in the voicing.
These “towers of notes” are certainly intimidating, but, in fact, are almost
never played that way by a keyboard or guitar player. In the previous
section we encountered examples of 9th chords using rootless voicing;
similar reductions are applied to 11th and 13th chords. Voicing becomes a
major issue with extended chords; each extension has its own “rules”.
The 13th is actually a 6th above the root of the chord, and, in fact, all the
extensions can be regarded in a similar way: the 11th is a 4th above the
3
root, and the 9th is a 2nd above the root. With reduced voicing, then, can
a 13th chord ever be the same as a chord with an added 6th? Look at the
following examples of chords with extensions, as compared with chords
that simply have an added note in the first octave:
1. 2nds and 9ths:
5b2
The “C2” chord (or C(sus 2))is unusual, and, without a third, could be
heard as either major or minor. All the rest are true 9th chords; notice
that the two “add 9” versions are missing a 7th, so the 9th is added to a
triad. The two 6/9 chords are very common, usually voiced in a reduced
form. In module 5a there were various examples of rootless voicings for
9th chords. Remember that 4-note versions usually look like common 7th
chords; for 3-note versions, the three “essential” notes are the 3rd, 7th,
and 9th. Look at the following examples:
5b3
4
There are many instances in the above examples, especially among the
3-note voicings, where another label could easily be applied: the Dm9
looks like an Fmaj7, the Gm9 looks like a Bbmaj7, etc. Realize,
however, that other chord notes could be in other parts, especially in the
bass.
There are frequent examples where a composer/arranger might label a
chord as a 9th chord, but add other notes for colour, especially the 13th:
5b4
Because each chord contains a 7th, the extra note is a 13th, not an added 6th.
The final example is labelled as a Gmaj7, but contains both the 9th and the
13th! This is a typical contradiction between jazz theory and jazz practice.
These voicing examples are all taken from actual keyboard parts, either
written for a small jazz ensemble or a big band.
2. 4ths and 11ths:
5b5
Beginning with a major triad, virtually every chromatic note in the octave
can be added to the chord as part of an altered chord or extension,
except for one note: the Perfect 4th above the root. Sometimes the 4th is
called the “avoid note”; if it’s added to a major chord, or even just given
too much emphasis in an improvisation it really sounds wrong. Given the
right context, however, a 4th may be added to a triad, 7th, or 9th chord,
with the 3rd omitted. These chords will have “sus” added to the label; an
5
abbreviation for suspension. In classical harmony the suspension is a
very common musical device. It’s always on a strong beat, and creates
tension because it temporarily replaces a chord note, then moves down
one step to the chord note to release the tension. The most common
suspension is the 4-3 suspension:
5b6
In jazz harmony the suspension sometimes resolves (moves down a step
to the 3rd of the chord), but just as frequently doesn’t resolve at all; in
this case it’s really an “added 4th”, not a suspension, but is always
labelled as “sus” in common practice, and the 3rd is almost never included
in a “sus” chord. (Is it major or minor?) As mentioned earlier, the true
11th (octave + P4th) is seldom used with a major chord where it clashes
with the 3rd an octave below. In the examples above the 11th is used
with a minor chord below, producing a major 9th against the 3rd of the
chord, a much “softer” dissonance than it would be with a major chord.
The next example shows the #11 used with various major chords,
producing that same “softer” major 9th against the 3rd below.
3. Sharp 11ths
5b7
The #11 is a common extension, and is almost always used with a major
chord. It does add a particular colour to the chord which is easily
recognized: the tritone (augmented 4th) against the root below. Full 11th
chords contain six different notes, so are almost never played that way.
6
Look at the following examples; for either 11th or #11th chords the
essential notes are the 3rd, 7th, and 11th. For a simple “sus” chord the
root, 4th, and 5th are essential, but “sus” chords often appear with added
7ths and 9ths as well. In the first two #11 chords in the example below,
the #11 is spelled enharmonically.
5b8
4. 6ths and 13ths:
5b9
13th chords actually appear quite often, even in pieces with few
extensions where most of the harmony is 7th chords. This is true in 19th
century Classical music as well, where the V13 often appears as a
dramatic climax at the cadence. It can almost be assumed that,
whatever notes are omitted from the 13th chord, the 7th should always be
there; this clearly produces the “13th sound”, which is entirely different
from an added 6th chord. For the 13th chord the 7th and the 13th are
essential notes, as well as the 3rd to identify the chord as major or minor.
Here are some sample voicings for the 13th chord:
7
5b10
There is much to be learned from studying these examples, all taken from
jazz ensemble keyboard parts. The first three examples include the
three essential notes as well as the root in the first example, the 9th in
example 2, and the flatted 9th in example 3. In example 4 the root is
added, and the 5th is added as well in example 5. Example 6 is unusual
because the 13th is now below the 7th, producing a dissonant minor
second. Examples 7 and 8 add the 11th for the first time, but it’s the #11
to avoid a strong clash with the 3rd. If the C were used here there would
be two major 7th/minor 2nd intervals in the chord. The final two
examples do introduce the natural 11th to the chord, but it’s disguised
with the sus label… which means the 3rd has been replaced…no clash!
In these examples, as well as previous ones in the lesson, there is a
common principle in all the various voicings: The extensions are never in
the bass; but always in the upper voices. This is only logical: the 11ths
need a root or third below; the 13th almost always has the 7th below.
8
Something to listen to:
The Boy (or Girl) Next Door has two #11 chords in the melody of the first
phrase, setting the character for the piece. Find one of the several
versions by Frank Sinatra; some versions include the verse at the
beginning.
Chelsea Bridge by Billy Strayhorn also has prominent #11’s in the first
phrase, and other extended chords throughout the piece. Check out the
1961 recording by the Duke Ellington Orchestra.
Take the A Train by Duke Ellington. The famous piano introduction is
built around a D7(#11) chord, which returns in the tune. Look for the
Ellington version.
There are dozens of “contemporary” big band arrangements from the
past 10 years that feature the harmonic language of extensions and sus
chords. Check out Mossman’s Samba Kinda Mambo; there are several
good performances by high school and college bands.