Chord Structure · Lesson 3
The Five Seventh Chords
about 15 min
What this lesson is for
Stack one more third on a triad and you have a seventh chord. Adding the seventh guarantees a dissonance inside the chord, so the chord itself starts demanding resolution. This lesson covers the five types in practical use and why the dominant seventh is the important one.
- Explain a seventh chord as a four-note chord made by adding a third to a triad
- Describe the five practical types (maj7, m7, 7, m7b5, dim7) as a triad plus a seventh
- Explain that the dominant seventh contains a tritone, and why that drives its resolution
- Explain that seventh chords have four inversions, figured 7, 6-5, 4-3, and 4-2
In this lesson
Stack one more third on a triad and you have a four-note chord. Counting from the root, the new note is a seventh, so these are seventh chords.
One extra note sounds like a small change, and the change is qualitative. A seventh is always a dissonant interval, so a seventh chord always carries tension inside itself.
Triad plus seventh
In principle there are four triad types times three seventh qualities. In practice five combinations do essentially all the work.
| Name | Triad | Seventh added | Symbol | Where it is used |
|---|---|---|---|---|
| Major seventh | major | major 7th | maj7 | on I and IV (gentle) |
| Minor seventh | minor | minor 7th | m7 | on ii, iii, vi |
| Dominant seventh | major | minor 7th | 7 | on V (the crucial one) |
| Half-diminished seventh | diminished | minor 7th | m7♭5 | vii in major, ii in minor |
| Diminished seventh | diminished | diminished 7th | dim7 | vii in minor |
Note the B♭♭ in the diminished seventh chord. On a keyboard that is A, but writing A would make it the sixth degree instead of the seventh. The principle from Unit 0 — the letter determines the degree — turns out to be load-bearing here rather than pedantic.
The five compared
Check: The root is C throughout. maj7 floats softly; m7 is a settled kind of dark; the dominant seventh is unmistakably impatient to move; m7♭5 hangs suspended; dim7 is the most strained of all. The point is that all five are tense in different ways, not that some are more tense than others.
major triad + major 7th
Check
What are the notes of Am7?
Which sevenths the scale produces
The “where it is used” column above is not a matter of opinion. Taking every other note of the scale four times determines automatically which type lands on which degree. It is the triad procedure with one more note.
Two consequential facts come straight out of this figure.
First, major keys produce no diminished seventh chord. That is why the table above lists dim7 as belonging to minor. Diatonic major yields only four types: major seventh, minor seventh, dominant seventh, and half-diminished.
Second, there is exactly one dominant seventh among the seven. A major triad with a minor 7th on top occurs only on V within a major key. So hearing a dominant seventh is enough to identify the key. The mechanism gets a closer look below.
Check
Which of these does not occur among the diatonic seventh chords of a major key?
Minor keys cannot produce a dominant seventh
Running the same procedure in minor gives an interesting result.
In natural minor — A B C D E F G for A minor — the chord on V comes out as Em7 (E G B D). E to G is a minor 3rd, so it is a minor seventh chord, and no dominant seventh is available.
The power of the dominant seventh comes from two simultaneous half-step motions, the leading tone rising and the seventh falling. With G as the seventh degree there is no half step below the tonic A, so that drive never materializes.
The fix is harmonic minor, with the seventh degree raised: A B C D E F G♯. Now the chord on V is E7 (E G♯ B D), and the dominant seventh exists.
This is the concrete reason harmonic minor is needed. Unit 2 put it as “raise the seventh degree to get a leading tone.” The purpose of getting that leading tone was, specifically, to be able to build a dominant seventh.
The two versions of V in minor
Check: Both are V to i in A minor. The first uses Em7 from natural minor; the second uses E7 from harmonic minor. One note differs, G against G♯, and the inevitability of the landing is transformed. The third isolates the tritone inside E7 — those two notes are the whole engine.
not a dominant seventh — the drive is weak
One further observation: stacking sevenths through harmonic minor produces seven chords of seven different types (ImM7, IIm7♭5, IIImaj7♯5, IVm7, V7, VImaj7, VIIdim7). Where major recycles four types, harmonic minor carries an augmented 2nd inside the scale, and that distortion scatters the chord qualities as well. The sense that minor-key harmony is more complicated than major is grounded in this structural difference.
Check
What has to happen for a minor key to have a dominant seventh (V7)?
Why the dominant seventh is the important one
Of the five, the dominant seventh matters far more than the rest, and the reason is structural.
Stacking a seventh on V in C major gives G–B–D–F, which houses two significant notes at once:
- B = the leading tone, a half step below the tonic C
- F = the seventh, a half step above E
And the interval between those two is a diminished 5th, a tritone. Unit 1 established that a tritone spelled as a diminished interval wants to contract inward. Here it actually does.
B goes up, F goes down, both by a half step. That double half-step resolution gives the dominant seventh a directedness no other chord can match.
Which is why the dominant seventh is not decoration on V but a device for establishing a key. Sound a dominant seventh and the identity of the chord that follows is close to determined. The secondary dominants and modulation techniques in Unit 8 all exploit this property.
How much the seventh adds
Check: First V to I with plain triads, then V7 to I. One added note noticeably sharpens the inevitability of the resolution. The third stops on V7 without resolving, leaving the question audibly open.
Check
When a dominant seventh resolves, which way does its seventh move?
Seventh chords have four inversions
Four notes means four arrangements, and figured bass accordingly has four forms.
| Position | Note in the bass | Figured bass | Roman numeral (on V) |
|---|---|---|---|
| Root position | root | 7 | V7 |
| First inversion | third | 6⁄5 | V65 |
| Second inversion | fifth | 4⁄3 | V43 |
| Third inversion | seventh | 4⁄2 | V42 |
The figures work exactly as in the previous lesson. First inversion has B in the bass, and B to F is a fifth while B to G is a sixth, giving 6⁄5. Third inversion has F in the bass, and F to G is a second while F to B is a fourth, giving 4⁄2.
The one with distinctive practical value is third inversion (V42). With the seventh in the bass, the bass itself resolves down by a half step (F to E). It is the standard way of making a bass line move chromatically at a cadence.
When to use seventh chords
How much sevenths get used varies enormously by style.
- Classical harmony: triads are the default; V7 dominates the seventh chords and others are limited
- Romantic period onward: seventh chords proliferate and chains of tension grow longer
- Jazz: seventh chords are the baseline, and a bare triad registers as thin
- Pop and rock: mostly triads, with maj7 and m7 used for color
So “should I use a seventh chord here” is not a question theory answers. It is a question of style. Play I–vi–ii–V with triads and it sounds like folk; play it with sevenths and it sounds like jazz.
One progression, two styles
Check: The progression is I–vi–ii–V in both. The first uses triads only, the second sevenths throughout. The harmonic skeleton is unchanged while the stylistic signal is completely different — a concrete case of style, not theory, making the decision.
I–vi–ii–V
Exercises
Every answer here is cross-checked against the theory engine. Work them out before you grade.
- 1
Spell G7, the dominant seventh chord, from the bottom up, using single spaces between names.
- 2
Spell Cmaj7 from the bottom up, using single spaces between names.
- 3
Spell Bm7b5, the half-diminished seventh chord, from the bottom up, using single spaces between names.
- 4
In G7, which two notes form the tritone?
- 5
Which figured bass indicates the third inversion of a seventh chord?
Before you move on
Check that you can explain each point above in your own words.