Extensions and tensions
Ninths, elevenths and thirteenths, how they're added to seventh chords and which tensions work over each chord type.
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Content under musical review. It may contain inaccuracies.
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Ninths, elevenths and thirteenths, how they're added to seventh chords and which tensions work over each chord type.
Advanced
Keep stacking thirds on a seventh chord and you reach the ninth (9), the eleventh (11) and the thirteenth (13). They're the second, fourth and sixth of the scale, an octave higher. They're called extensions or tensions because they add colour without changing the chord's function: a G13 is still a dominant.
A C7, then the same chord with a ninth:
A Cmaj7 against a Cmaj9:
And a dominant with a flat ninth, darker and more tense:
| Extension | Same as | On C | Example symbol |
|---|---|---|---|
| 9 | 2 + octave | D | C9, Cmaj9, Cm9 |
| 11 | 4 + octave | F | Cm11 |
| #11 | #4 + octave | F♯ | Cmaj7♯11 |
| 13 | 6 + octave | A | C13 |
A symbol like C13 implies the seventh (and usually the ninth); Cadd9, on the other hand, is a triad plus a ninth without a seventh.
String 6, Open: E2 · 13 · Tension
Six or seven notes don't fit comfortably on a guitar, so you choose. Tap these diagrams and notice which degrees appear:
A practical rule for choosing which notes to play:
Not every tension suits every chord. Levine groups them like this:
A quick way to add colour: play a four-note voicing (root, third, seventh) on strings 6 to 3 or 5 to 2, and put the tension on the highest string. The tensions' own melody (9 falling to 8, 13 falling to 5) already creates a small inner movement.
maj9 chord on COn a dominant that resolves to a minor chord, the tensions come from the target's harmonic minor: E7♭9 before Am contains F (b9) and C (b13), both notes of A minor. The symbol G7alt calls for all four alterations (b9, #9, #11 and b13) and goes with the altered scale, the seventh mode of A♭ melodic minor.
Persichetti treats these chords as part of tertian harmony, all the way up to the thirteenth chord. On guitar, which notes you leave out and how you order them completely changes the sound.