This lesson continues the sequence of jazz piano materials by extending the chord vocabulary introduced in Triads and 7th Chords. If you have arrived directly at this page, the guiding assumption is that you already understand basic triad and seventh-chord construction and are comfortable relating chord formulas to the major scale.
Here, we move beyond four-note chords and address how jazz harmony expands through extensions and how dominant chords are commonly altered to increase tension and forward motion. The goal is not memorization for its own sake, but functional literacy: being able to quickly interpret chord symbols and make informed musical decisions at the keyboard.
Chordal Extensions
Most jazz chords are constructed by stacking thirds. When this process continues beyond the octave, the added notes are referred to as extensions. These extensions are not new pitch classes, but higher-order equivalents of familiar scale degrees.
A useful way to think about extensions is through their octave displacement:
- 9 = 2
- 11 = 4
- 13 = 6
Understanding this relationship allows you to decode chord symbols efficiently and reinforces the idea that all chord formulas ultimately relate back to the major scale.
Alterations to Dominant Chords
In functional jazz harmony, dominant chords are frequently altered to heighten tension before resolving to their corresponding tonic. The most commonly altered tones are the 9th and the 5th.
These alterations introduce chromatic color and increase the sense of pull toward resolution.
Altered 9ths: b9, #9
Altered 5ths: b5 (enharmonically #11), #5 (enharmonically b13)
Most chord symbols encountered in straight-ahead jazz contexts are summarized on the attached handout,
Chord Symbol Notation & Identification. Study this carefully and practice constructing chords in multiple keys using numeric formulas, always referenced to the major scale.
Rules, Tendencies, and Useful Conventions
Rather than rigid laws, the following are common conventions that will help you interpret chord symbols quickly and consistently. Over time, listening and experience will refine how you apply them.
- 9 implies the presence of a 7.
- 11 implies the presence of a 9 and a 7.
- 13 applies only to dominant chords; use 6 for major and minor chords.
- 13 implies 9 and b7, but does not imply 11 or #11.
- For half-diminished chords, use b5 (not its enharmonic #11).
- For major chords, use #11 (not b5).
- For dominant chords, #11 and b5 are both acceptable.
Homework Practice Assignments
- Chord Construction: Each day, construct all chords listed on the Chord Symbol Notation & Identification handout in two keys. Divide this into two shorter practice sessions.Example: Day 1 — C and Db; Day 2 — D and Eb; continue chromatically.
- Extensions & Alterations Drill:
Create two sets of cards: one with all 12 chromatic roots, and one with extensions and alterations (9, 11, 13, b9, #9, b5, #5, b13, #11).
Draw one card from each stack and construct the resulting chord at the keyboard.