Module 3: Theory II: seventh chords and the ii–V–ILesson 1beginner⏱ 75 min + two weeks of daily shape and arpeggio drills

Seventh chords

Learn the formulas, spellings and sounds of the eight seventh-chord qualities, and play each one as an arpeggio and as a root-position drop-2 and drop-3 shape.

Why four notes

A triad tells you whether a chord is major or minor. The fourth note tells you what the chord does. Add a major 7th to a C major triad and you have a chord that sits still; add a minor 7th instead and the same triad wants to move somewhere. Jazz harmony lives on that distinction. When you read "the ii chord", "the V chord" or "the I chord" in the rest of this course, each of those is a particular seventh-chord quality, and the quality is what makes the progression work.

There are eight qualities you must own completely: major seventh, dominant seventh, minor seventh, half-diminished (minor seven flat five), diminished seventh, minor-major seventh, major sixth and minor sixth. Everything else on a chart is one of these with notes added or altered. This lesson teaches you to spell them, hear them and play them. If you have not finished Triads, do that first: every seventh chord here is a triad plus one note.

From triad to seventh chord

A seventh chord is a triad with another third stacked on top, which puts the new note a seventh above the root. Three kinds of seventh appear in these chords:

• the major 7th, 11 semitones above the root (one fret below the octave);
• the minor 7th, 10 semitones (two frets below the octave);
• the diminished 7th, 9 semitones. It sounds the same as a major 6th, and on the guitar it is the same fret, but in a diminished seventh chord it is spelled as a seventh because the chord is built in thirds.

The sixth chords (6 and m6) are the exception that proves the rule: instead of a seventh they add the major 6th (9 semitones) to a major or minor triad. They are treated as seventh-chord family members because they do the same jobs on a chart.

Combine the four triad types from Module 2 with these sevenths and you get the table below. Read the "Formula" column as scale degrees of the major scale starting on the root, exactly as you did for triads: a flat sign lowers the degree by one fret.

The eight qualities, one by one

Learn them in families. The family tells you where a chord shows up on a chart and which chords can replace each other.

Major family: maj7 and 6

Major seventh (maj7, also written Δ7 or M7) is a major triad plus the major 7th. It is the sound of a tonic chord at rest, the I chord in a major key, and also the IV chord. The major 7th sits a half step below the root, so when the melody lands on the root a maj7 voicing can clash; that is why players often choose the major sixth (6) for a I chord when the melody is on the root. Both chords are interchangeable as tonics; the 6 chord is the older, swing-era sound, the maj7 the modern one.

Dominant family: 7

Dominant seventh (7) is a major triad plus the minor 7th. The 3rd and the 7th are a tritone apart, and that unstable interval is why the chord wants to resolve, normally to a chord whose root is a perfect 5th lower. The V chord in a major key is a dominant seventh, and so is every chord in a blues. When a chart just says "C7", with no "maj" and no "m", it means this chord.

Minor family: m7, m6 and mMaj7

Minor seventh (m7, also –7 or min7) is a minor triad plus the minor 7th. It is the ii chord, the iii chord and the vi chord of a major key, and the most common minor chord on any chart. It sounds soft and unresolved; a m7 chord nearly always moves on to a dominant chord.

Minor sixth (m6) and minor-major seventh (mMaj7, or m(maj7), or –Δ7) are the two sounds of a minor tonic, the i chord in a minor key. Compare the table: m6 raises the 7th of m7 by a whole step to the 6th; mMaj7 raises it by a half step to the major 7th. Both belong to the melodic minor scale, which is why that scale is called the jazz minor. The m6 is the warm, settled, film-noir minor; the mMaj7 is the dramatic one with the semitone rub between the 7th and the root. Neither is a ii chord: when you see Dm6 or DmMaj7 on a chart, the tune is in D minor, not in C major.

Diminished family: m7b5 and dim7

Half-diminished (m7b5 or ø7) is a diminished triad plus the minor 7th. It is the vii chord of a major key and, far more importantly, the ii chord of a minor key, which is where you will meet it constantly from lesson 4 onwards.

Diminished seventh (dim7 or °7) is a diminished triad plus the diminished 7th. All four notes are a minor 3rd apart, so the chord is perfectly symmetrical and has no clear root; it is used as a passing chord between diatonic chords and as a stand-in for a dominant 7b9 chord. Module 11 explores that symmetry.

Spelling any seventh chord

Three steps, and you can spell any seventh chord from any root in a few seconds:

1. Write four alternating letters starting on the root. From E that is E–G–B–D; from Bb it is B–D–F–A with whatever accidentals come next. Never skip this step: a seventh chord always uses every other letter, which is why the 7th of a Cdim7 is, strictly, a double-flat B (two half steps below B). In practice almost everyone, including the tables in this course, writes the simpler enharmonic name for that one note; the quizzes accept either spelling.
2. Spell the major triad from the root using the key signature of the root's major key (Module 2 covered key signatures), then adjust the 3rd and 5th for the quality: flat the 3rd for minor, flat the 5th too for diminished.
3. Add the 7th: major 7th = the 7th degree of the root's major scale; minor 7th = that note flattened; diminished 7th = flattened twice (so it often carries a double flat). For 6 and m6 add the 6th degree of the major scale instead.

Check your work against the generated table for several other roots:

Notice in that table how the diminished seventh's 7th is shown by its simpler enharmonic name (the strict letter-rule spelling would be a double flat, or an F-flat for Gdim7), and how the sixth chords borrow the 6th degree rather than any 7th. The Chord dictionary spells any symbol you type; use it to check yourself, not to avoid the work.

Hearing the qualities

Play the following eight chords slowly and listen for the character of each. All eight use the same drop-2 shape family on strings 5–4–3–2, with the root on the 5th string at the 3rd fret, so the only thing that changes from chord to chord is the quality.

\tempo 60
.
\ts 4 4
:1 (3.5 5.4 4.3 5.2){ch "Cmaj7"} | (3.5 5.4 3.3 5.2){ch "C7"} | (3.5 5.4 3.3 4.2){ch "Cm7"} | (3.5 4.4 3.3 4.2){ch "Cm7b5"} |
(3.5 4.4 2.3 4.2){ch "Cdim7"} | (3.5 5.4 4.3 4.2){ch "CmMaj7"} | (3.5 5.4 2.3 5.2){ch "C6"} | (3.5 5.4 2.3 4.2){ch "Cm6"} |

What to listen for:

• maj7: bright and complete; nothing needs to happen next.
• 7: the same brightness with a pull. Play it and then play the maj7 chord a 5th lower (here that would be Fmaj7) to hear it resolve.
• m7: darker, soft, still open-ended.
• m7b5: tense and hollow; the flat 5th makes it sound like a question.
• dim7: unstable, all tension; it wants to slide somewhere by a half step.
• mMaj7: minor with an edge; the semitone between the 7th and the root is the "spy film" sound.
• 6: warm and settled, the classic swing tonic.
• m6: minor and settled, with a hint of sweetness from the 6th.

Then test yourself in the Ear trainer with the chord-quality drill set to these eight types. Hearing the quality is the goal; being able to name it is the proof.

Arpeggios: the chord one note at a time

An arpeggio is a chord played one note at a time. Arpeggios are how improvisers "play the changes", and they are the fastest way to make the formulas physical. All of these start on the root on the 5th string at fret 3 and stay within frets 1–5, one position, so you can concentrate on the sound of each degree.

\tempo 80
.
\ts 4 4
:8 3.5{ch "Cmaj7"} 2.4 5.4 4.3 5.3 4.3 5.4 2.4 | 3.5{ch "C7"} 2.4 5.4 3.3 5.3 3.3 5.4 2.4 |
3.5{ch "Cm7"} 1.4 5.4 3.3 5.3 3.3 5.4 1.4 | 3.5{ch "Cm7b5"} 1.4 4.4 3.3 5.3 3.3 4.4 1.4 |

\tempo 80
.
\ts 4 4
:8 3.5{ch "Cdim7"} 1.4 4.4 2.3 5.3 2.3 4.4 1.4 | 3.5{ch "CmMaj7"} 1.4 5.4 4.3 5.3 4.3 5.4 1.4 |
3.5{ch "C6"} 2.4 5.4 2.3 5.3 2.3 5.4 2.4 | 3.5{ch "Cm6"} 1.4 5.4 2.3 5.3 2.3 5.4 1.4 |

Practise these with a metronome at 60–80 bpm first, playing the chord shape from the previous section at the start of each bar and then the arpeggio, so your ear links the vertical sound to the horizontal one.

Your first four-note shapes

A four-note chord in close position has all its notes within one octave, stacked in thirds. On a piano that is easy; on a guitar it is usually unplayable. Guitarists therefore use open voicings made by dropping one note down an octave:

• Drop 2: take the second note from the top of a close voicing and drop it an octave. The result fits on four adjacent strings.
• Drop 3: take the third note from the top and drop it an octave. The result spans five strings with one string skipped (muted).

For now you need only root-position shapes, where the root is the lowest note. Later modules add the other three inversions of every shape. Three shape families cover the three most useful string sets.

Drop 2 on strings 5–4–3–2

From the bass up, a root-position drop-2 voicing lays out as root, 5th, 7th, 3rd. The root is on the 5th string, so you already know where to put every chord: find the root with your fretboard note names and the shape does the rest.

Compare them in pairs. Cmaj7 to C7 moves one finger (the 7th) down a fret. C7 to Cm7 moves the 3rd down a fret. Cm7 to Cm7b5 moves the 5th down a fret. Cm7b5 to Cdim7 moves the 7th down a fret. These are exactly the one-note differences in the formula table, now under your fingers.

Drop 2 on strings 4–3–2–1

The same voicing order (root, 5th, 7th, 3rd) on the top four strings, root on the 4th string. The sound is brighter and the shapes are a little tighter because of the B-string tuning offset.

Drop 3 on strings 6–4–3–2

Drop-3 root-position shapes put the root on the 6th string, skip the 5th string (mute it with the fretting finger that holds the root), and lay out as root, 7th, 3rd, 5th. These are the big, full "Joe Pass" chords, and they are the ones you will comp with most in Module 4 and beyond.

Exercises

1. Quality ladder. On one string set, play the eight qualities in the table order on a single root, two beats each, with a metronome at 60 bpm. Name each chord aloud before you play it. Do all three string sets.
2. Chord then arpeggio. Play a shape, then its arpeggio from the root up and back down within the same position, then the shape again. One quality per minute; eight qualities a day.
3. New roots. Move each shape family to the roots of the chords in the second table above. Play the chord, say the spelling, then check the spelling against the table.
4. Ear check. Have a friend (or the ear trainer) play a quality; you name it, then play it on the nearest shape.

Quiz