Extensions and tensions

Listen to the same C chord dressed four ways. Notice how the feeling changes even though the function (tonic) stays the same:

Play: C: the triad Play: Cmaj7: soft, open Play: Cmaj9: adds the 9 (D) Play: C6/9: bright, no seventh

The D in Cmaj9 is the same note as the second degree of the scale, but placed above the chord tones it sounds like a colour, not a passing note. That is the whole idea of an extension.

A chord is built by stacking thirds: 1, 3, 5, 7. Keep stacking and the 9, 11 and 13 appear, which are degrees 2, 4 and 6 an octave higher. After the 13 you are back at the root: you have used all seven notes of the scale.

That's why every tension depends on the chord's scale. Here is the map in C major, the same chord-scale idea you saw with the modes:

Why is the 11 "too much" on Cmaj7? Because F sits a half step above E, the chord's third. Held together, the 11 masks the third and the chord stops sounding major and stable. Hear the difference:

Play: Cmaj7 + 11: the F clashes with the E Play: Cmaj7 + #11: the F# shines (Lydian sound)

An avoid note isn't forbidden: in a melody it can pass by without any problem. What you avoid is holding it in the chord or ending a phrase on it. On a dominant, the 11 turns into a new chord if you remove the third: G7sus4 is exactly that.

Minor chords are more generous

On a minor chord the 11 doesn't get in the way: it lies a whole step above the ♭3, not a half step. That's why Dm11 sounds open and modern, very typical of modal jazz and neo-soul. Hear a voicing in fourths with the 11 on top:

Play: Dm11: 1, b7, b3, 11 Play: Am9: 1, b7, b3, 9

On iii (Em7, Phrygian), by contrast, the F sits a half step above the root and sounds harsh; and on vi (Am7, Aeolian) the F rubs against the fifth. Once again, the chord's scale decides. On the half-diminished chord (Bm7♭5) the 11 (E) is the most used tension.

The guitar has six strings and four useful fingers, so you can't play a thirteenth chord with all seven notes. Nor do you need to. Follow these priorities:

1. Third and seventh, always: they define the chord type.
2. The tension you want to hear, ideally on top, in the highest voice.
3. The root only if there's no bass player.
4. The fifth is the first to go: it hardly ever adds anything.

Hear them in a ii–V–I: the tensions create inner lines that move in small steps, like a horn section.

1. 1Dm9ii9
2. 2G13V13
3. 3Cmaj9Imaj9
4. 4C6/9I6/9

The dominant is the most tolerant chord: it accepts all four altered tensions. An altered dominant sounds tenser and resolves more strongly:

Play: G13: natural tension Play: G7b9 Play: G7#9 Play: G7b13

And their guitar shapes, all on the same G7 shell (G on the sixth string, F on the fourth, B on the third). Only the top strings change:

Theory deep diveWhen natural and when altered?

There's a tonal logic behind it:

• If the dominant goes to a major chord, the tensions of its Mixolydian scale (9 and 13) are the "natural" ones, and the altered ones are extra colour.
• If it goes to a minor chord, the key itself already gives it b9 and b13: E7 → Am calls for F and C, which are the b9 and b13 of E. It's the Phrygian dominant from the previous stop.
• A #11 with natural 9 and 13 gives the Lydian dominant sound (D7♯11), much used on V/V and on dominants that don't resolve.
• The b9 and the natural 9 are not combined in the same voicing: pick one.

The symbol 7alt means "you choose the alterations", usually b9, #9, b13 and #11 together. You'll meet the scale that contains them all two stops from now.

An ear for altered tensions is one of the skills that most separates an intermediate guitarist from an advanced one. The trick is to listen to the top voice and its resolution, not to the chord as a block. Hear how the ♭9 of G7♭9 falls a half step to the fifth of C:

In the first bar the top voice falls a half step (A♭ → G); in the second, a whole step (A → G). The b9 sounds darker and "asks" more strongly for the resolution.

Practice

ii–V–I with tensions

60–100 BPM8 min

1. Play each voicing on its own and check that the four fretted strings ring and the others are muted.
2. Find the shortest path between them: from Dm9 to G13, the finger on the seventh (C) drops to B.
3. Play along with the backing using a comping rhythm: short hits on 2 and 4.

1. 1Dm9ii9
2. 2G13V13
3. 3Cmaj9Imaj9
4. 4Cmaj9Imaj9

Goal: Link Dm9 – G13 – Cmaj9 at 90 BPM in quarter notes, with no string cutting out and moving only the fingers you have to.

Practice

From natural to altered

60–90 BPM6 min

1. Play G13 (3x345x), then G7♭9 (3x34x4) and resolve to Cmaj9 (x3243x).
2. Sing the highest note of each chord. You'll notice the b9 pushes hard downwards.
3. Repeat, swapping G7♭9 for G7♯9, G7♭13 and G7alt. Pick your favourite.

1. 1G13V13
2. 2G7♭9V7b9
3. 3Cmaj9Imaj9
4. 4Cmaj9Imaj9

Goal: Play G13 → G7b9 → Cmaj9 five times in a row while singing the top voice (E → Ab → G).

Self-assessment

Which scale degrees are the 9, 11 and 13 equivalent to?

A2, 4 and 6B3, 5 and 7Cb2, b4 and b6

On Cmaj7, which is the avoid note?

AThe 9 (D)BThe 13 (A)CThe 11 (F)DThe 7 (B)

In a guitar voicing with tensions, which note is usually left out first?

AThe fifthBThe thirdCThe seventhDThe tension you want to hear

Listen to this G dominant. Which tension is on top?

Listen

AA natural 9BA b9CA 13

What usually makes a chord with tensions sound muddy?

AMixing the b9 and the natural 9BPutting a third and a ninth on the sixth stringCBoth

Optional reinforcement in the portalExplore more G13 voicings and their alterations(opens in a new tab)