Module 9: Scales and modesLesson 2advanced⏱ 90 min + two weeks of drills

Chord-scale theory and available tensions

Learn which tensions each chord type accepts, why the avoid notes are avoided, how to run a ii–V–I by chord-scale, and where chord-scale thinking stops being useful.

Why a scale is only half of the answer

The previous lesson paired each diatonic chord with a mode. That is the start of chord-scale theory, the idea that every chord symbol implies a seven-note scale, and that the scale tells you which notes are "in" over that chord. It is the dominant teaching method in jazz education and it is genuinely useful: it gives you a complete palette for every chord, it explains where tensions such as 9, 11 and 13 come from, and it lets you read a chart full of 7#11 and 7alt symbols without guessing.

It also has a well-known failure mode: students learn the scales and then play scales. This lesson gives you the theory properly, so that you know exactly which notes a chord accepts and which it does not, and then draws the line around it, so that you keep playing lines that use the theory rather than scales that demonstrate it.

Tensions: the chord continued past the 7th

A seventh chord is a stack of 3rds: 1 3 5 7. Keep stacking and you get 9, 11 and 13, which are the 2nd, 4th and 6th of the scale an octave higher. Every seven-note chord-scale therefore divides into four chord tones (1 3 5 7) and three tensions (9 11 13), and a tension can be natural, raised or lowered depending on the scale. In Voicings II you played these as chord voicings; here they are melodic choices.

The engine's chord dictionary shows which tensions each symbol carries. Read the formula column: it is the list of degrees a melodic line may land on freely over that chord.

A tension is available when it can be held over the chord without the chord's quality changing or a chord tone being contradicted. The rule that predicts availability almost every time:

A note that sits a whole step above a chord tone is an available tension. A note that sits a half step above a chord tone is an avoid note (unless the chord symbol asks for it explicitly, as 7b9 does).

The reason is physical. A note a half step above a chord tone produces a minor 9th against it, the harshest interval in tonal music, and the ear hears the lower note as being contradicted. A note a whole step above produces a major 9th, which simply sounds like colour.

Available tensions by chord type

Apply the whole-step rule to each common chord type with its first-choice scale, and the familiar lists appear. The tables above and below back every claim; the summary here is what to memorise.

Major 7th (Ionian): 9 and 13 are available, both a whole step above a chord tone. The natural 4 (11) sits a half step above the 3rd, so it is the avoid note; the maj7 chord loses its major quality the moment the 4 is held. Major 7th (Lydian): the #11 is a whole step above the 3rd and is fully available, which is why Lydian is so popular on major chords: it has no avoid note.

Minor 7th (Dorian): 9, 11 and 13 are all available (the 11 is a whole step above the b3). Minor 7th (Aeolian): the b6 (b13) sits a half step above the 5th and is the avoid note. Minor 7th (Phrygian): both b9 and b13 are avoid notes by the rule, which is why Phrygian is a "stay in the key" choice on iii rather than a colour you hold.

Dominant 7th (Mixolydian): 9 and 13 available; the 4 (11) is a half step above the 3rd and is the avoid note. It is called a "sus" note for the same reason: hold it and the chord becomes 7sus4. Dominant 7th with alterations: the chord symbol overrides the rule. 7b9 asks for the b9 even though it is a half step above the root; the altered dominant of the next lesson asks for b9, #9, #11 and b13 together.

Half-diminished (Locrian): the b2 is a half step above the root and is avoided; Locrian natural 2 from melodic minor fixes this and is the modern choice, as the next lesson shows.

Here is the whole-step rule in sound. Over Cmaj7, the chord tones first, then the 9 and 13, then the 4 held against the 3rd so you can hear why it is avoided, and its resolution.

\tempo 80
.
\ts 4 4
:4 8.6{ch "Cmaj7"} 7.5 5.4 4.3 | :8 7.3{txt "9"} 5.2 7.4{txt "13"} 4.3 :2 8.1 | :2 6.2{txt "4: avoid"} :4 5.2{txt "3"} 7.3 | :4 5.2 :8 7.3 5.3 :2 5.3 |

The avoid note is not forbidden. It is a passing note and an approach note, and you will use it constantly on weak beats. "Avoid" means: do not land on it, do not hold it, do not end a phrase on it over this chord.

Chord-scale choices for the chords you meet

The chord-scale table lists, for each symbol, every scale in the engine's library that contains all of its tones. The first listed is the default; the others are colours you choose on purpose.

Two things to notice. First, a plain m7 symbol has many candidates; the scale is a choice you make based on the chord's function (Dorian for ii, Aeolian for vi, Phrygian for iii, or Dorian on all of them if you want the brighter sound). Second, the more alterations the symbol carries, the fewer scales fit, until a 7alt symbol leaves only one. Chord-scale theory is at its most useful exactly there: a symbol like G7alt looks frightening and actually tells you precisely what to play.

Applying it to a ii–V–I

In a major-key ii–V–I all three chords come from one parent scale, so derivative thinking from the previous lesson already gives you the notes. Chord-scale theory adds the second layer: which notes are tensions on this chord, and which one is the avoid note.

Over Dm7 (Dorian) the 9, 11 and 13 are all free. Over G7 (Mixolydian) the 9 and 13 are free and the 4 is the avoid note. Over Cmaj7 (Ionian) the 9 and 13 are free and the 4 is the avoid note. The line below uses tensions on strong beats on every chord and is checked against chord symbols that include those tensions, so the engine confirms that every note is a chord tone or an available tension.

\tempo 132
.
\ts 4 4
:8 5.5{ch "Dm9"} 8.5 7.4 5.3 7.3 5.2 7.3 5.3 | 4.3{ch "G13"} 7.3 6.2 5.2 7.3 4.3 7.4 5.4 | 7.1{ch "Cmaj13"} 8.1 7.1 5.1 8.2 5.2 7.3 5.3 | :4 5.3 :8 7.3 5.2 :2 7.3 |

Compare it with the same progression where the line sits on the avoid note of the I chord. The engine passes this block, because every note is in C major, but your ear will not: the held 4 in bar 3 turns the Cmaj7 into something unresolved until it moves to the 3rd.

\tempo 132
.
\ts 4 4
:8 5.5{ch "Dm7"} 7.5 8.5 7.5 5.5 5.3 4.3 5.3 | 8.5{ch "G7"} 7.5 5.5 4.3 5.3 7.3 5.2 6.2 | :2 6.2{ch "Cmaj7"} :4 5.2{txt "resolve"} 7.3 | :4 5.2 :8 7.3 5.3 :2 5.3 |

The same contrast on the dominant: over G7, the 4 is the avoid note and the 13 is the colour. In this line the 4 appears only as a passing note between the 3rd and the 5th, while the 13 and 9 get the long notes.

\tempo 120
.
\ts 4 4
:8 3.6{ch "G7"} 5.6 2.5 3.5 2.5 5.5 2.4 3.4 | 2.4 5.5 3.5 2.5 :2 2.5 | :8 5.4 2.3 4.3 5.3 4.3 3.2 5.2 6.2 | :4 5.2 :8 5.3 4.3 :2 4.3 |

Dorian versus Aeolian on a minor chord

The clearest avoid-note case on guitar is the b6 on a minor seventh chord. Play a Dm7 vamp and run D Aeolian, treating the b6 strictly as a passing note, and then D Dorian, holding the natural 6. Both lines are correct; only one of them is a sound you would hold.

\tempo 112
.
\ts 4 4
:8 5.5{ch "Dm7"} 7.5 8.5 5.4 7.4 8.4 7.4 5.4 | 8.5 7.5 :4 5.5 :2 7.3 |

\tempo 112
.
\ts 4 4
:8 5.5{ch "Dm7"} 7.5 8.5 5.4 :2 4.3 | :8 5.3 4.3 7.4 5.4 :4 8.5 5.5 |

The fretboard maps make the one-fret difference visible: find the b6 in the Aeolian map and the 6 in the Dorian map, both in position V.

The limits of chord-scale thinking

Now the other half of the lesson. Chord-scale theory tells you which seven notes fit a chord. It does not tell you which of them to play, when, or in what order, and the great players before 1960 learned none of it. Four limits to keep in mind:

1. The scale is not the line. A line is built from chord tones on strong beats, approach notes and enclosures around them, and rhythm. Review approach notes: chromatic notes that are in no chord-scale at all are the most characteristic notes of bebop. If every note you play is "in the scale", your lines will sound like exercises.
2. One chord, one scale is a simplification. A G7 that resolves to C can take Mixolydian, Lydian dominant, the half-whole diminished, the whole-tone scale or the altered scale, and a good player may use two of them in one bar. The scale follows the sound you want, not the other way round.
3. Chords move. Thinking "D Dorian, G Mixolydian, C Ionian" on a fast ii–V–I is three thoughts where one ("C major, land on the guide tones") will do. Chord-scale theory is for the chords that leave the key: the 7#11, the 7alt, the maj7#5, the dim7. On diatonic chords, think key and chord tones.
4. Avoid notes are not wrong notes. A melody that lands on the 4 over a maj7 and resolves it is a suspension, one of the oldest devices in music. The theory says "do not hold it carelessly", not "never play it".

The right use of chord-scale theory is as a check and a palette: when a line is not working, ask whether you are holding an avoid note; when a chord is unfamiliar, ask which scale fits and which tensions it brings. Then go back to playing lines.

Exercises

1. Tension spelling. From the chord table, cover the notes column and spell 9, 11 and 13 for each symbol from memory, then check.
2. Whole-step rule. For each chord type, play the chord as an arpeggio on strings 5-4-3-2, then play each scale tone above it and decide by ear whether it is a tension or an avoid note before you look at the rule.
3. Tensions on downbeats. Over a looped ii–V–I, improvise 8 bars where every downbeat is a 9 or a 13 of the current chord. Then 8 bars where every downbeat is a chord tone. Then mix.
4. Avoid-note resolution. Over Cmaj7, play the 4 on beat 1 and resolve it to the 3rd on beat 2, in every octave and position you know. Do the same with the 4 on G7 and the b6 on Dm7 (Aeolian).
5. Scale choice. Take a standard you know in Roman numerals. For every non-diatonic chord, write the first-choice scale from the chord-scale table. For every diatonic chord, write "key".

Quiz