Seventh Chords Explained: The 5 Types and Half-Diminished vs Fully Diminished
Seventh chords are where harmony homework gets harder. A triad is either major, minor, diminished or augmented, and you can usually hear which. Add a fourth note and there are suddenly five common chord qualities, two of which look almost identical on paper. AP Music Theory, ABRSM theory papers and music school entrance tests all expect you to name them at sight. This guide gives you one table, a four-step method and a clear answer to the question that trips most students: half-diminished or fully diminished?
What is a seventh chord?
A seventh chord is a four-note chord built in thirds: root, third, fifth, seventh. It takes its name from the interval between the root and the top note of the stack, which is a seventh. Play C–E–G and you have a C major triad. Add B on top and you have Cmaj7; add B♭ instead and you have C7.
Two things decide the type of a seventh chord: the quality of the triad at the bottom (major, minor or diminished) and the size of the seventh above the root (major, minor or diminished). That is the whole system. Wikipedia's article on the seventh chord lists the rarer combinations too, but five types do nearly all the work in tonal music.
What are the five types of seventh chords?
Every chord in this table is built on C so you can compare them note by note.
| Type | Symbol on C | Notes | Triad + seventh | Where it lives |
|---|---|---|---|---|
| Major seventh | Cmaj7 | C – E – G – B | major triad + major 7th | I and IV in major |
| Dominant seventh | C7 | C – E – G – B♭ | major triad + minor 7th | V in major and minor |
| Minor seventh | Cm7 | C – E♭ – G – B♭ | minor triad + minor 7th | ii, iii and vi in major |
| Half-diminished | Cø7 (Cm7♭5) | C – E♭ – G♭ – B♭ | diminished triad + minor 7th | vii in major, ii in minor |
| Fully diminished | C°7 (Cdim7) | C – E♭ – G♭ – B𝄫 | diminished triad + diminished 7th | vii in minor |
Read the table from top to bottom and one note drops by a half step on each row: first the seventh (B to B♭), then the third (E to E♭), then the fifth (G to G♭), then the seventh again (B♭ to B𝄫). That's a good way to memorise the five types at the keyboard. B𝄫 sounds like A, but it's spelled as a kind of B because a seventh above C has to be some kind of B.
The dominant seventh is the one you'll meet first. Classical textbooks call it the major-minor seventh, because it's a major triad with a minor seventh. A sixth type, the minor-major seventh (C–E♭–G–B), turns up on the tonic of harmonic minor, but it's much rarer than the other five.
How do you identify a seventh chord in 4 steps?
- Stack the notes in thirds. You're given F–A–B–D. Rearrange until every note sits a third above the last: B–D–F–A. The lowest note of the stack is the root. If stacking is still slow, start with the guide to identifying piano chords.
- Name the triad. Look at the bottom three notes. B–D–F is a minor third plus a minor third: a diminished triad.
- Measure the seventh. Count from the root to the top note. B up to A is a minor seventh, one whole step below the octave. A major seventh sits a half step below the octave; a diminished seventh, a step and a half.
- Combine the two. Diminished triad plus minor seventh: half-diminished, Bø7. Then check the bass. The original chord had F at the bottom, so it's in second inversion. The chord inversions guide covers the figures 6/5, 4/3 and 4/2.
Half-diminished vs fully diminished: what's the difference?
Both chords sit on a diminished triad. The difference is the seventh, and it's one half step.
| Question | Half-diminished (ø7) | Fully diminished (°7) |
|---|---|---|
| Notes on B | B – D – F – A | B – D – F – A♭ |
| Seventh above the root | minor 7th | diminished 7th |
| Thirds in the stack | minor, minor, major | minor, minor, minor |
| Symbols | Bø7, Bm7♭5 | B°7, Bdim7 |
| Diatonic home | vii in C major, ii in A minor | vii in C minor (harmonic) |
| Typical use | ii of a minor ii–V–i | leading-tone chord pushing to the tonic |
Three things follow from that one note.
The name. "Half" diminished means only the triad is diminished; the seventh is an ordinary minor seventh. "Fully" diminished means both are diminished. Jazz charts write the half-diminished chord as m7♭5, which describes it from the other side: a minor seventh chord with a lowered fifth.
The symmetry. A fully diminished seventh is a stack of three minor thirds, and one more minor third brings you back to the root. It splits the octave into four equal parts, so every inversion sounds like another diminished seventh in root position, and there are only three different-sounding diminished sevenths on the whole keyboard. The half-diminished chord isn't symmetrical: its inversions sound clearly different from each other. Wikipedia's pages on the half-diminished seventh chord and the diminished seventh chord go further into both.
The key. In C major, B–D–F–A uses only white keys, so Bø7 is diatonic. B–D–F–A♭ needs an A♭ that C major doesn't have. It belongs to C minor, which makes B°7 in a C major piece a borrowed chord from the parallel minor.
Which seventh chords belong to a major key?
Build a seventh chord on every degree of C major, using only the notes of the scale, and you get four of the five types.
| Degree | Chord in C major | Notes | Type | Roman numeral |
|---|---|---|---|---|
| 1 | Cmaj7 | C – E – G – B | major seventh | Imaj7 |
| 2 | Dm7 | D – F – A – C | minor seventh | ii7 |
| 3 | Em7 | E – G – B – D | minor seventh | iii7 |
| 4 | Fmaj7 | F – A – C – E | major seventh | IVmaj7 |
| 5 | G7 | G – B – D – F | dominant seventh | V7 |
| 6 | Am7 | A – C – E – G | minor seventh | vi7 |
| 7 | Bø7 | B – D – F – A | half-diminished | viiø7 |
The pattern is the same in every major key: major sevenths on I and IV, minor sevenths on ii, iii and vi, one dominant seventh on V, one half-diminished on vii. So a dominant seventh chord points to exactly one major key. If you see G7, the key is very likely C.
The fully diminished chord is missing because it needs the raised leading tone of a minor key. In A minor, G♯–B–D–F is vii°7. Minor keys also put the half-diminished chord on the second degree: Bø7 is iiø7 in A minor, the first chord of the minor ii–V–i (Bø7 – E7 – Am). Puget Sound's page on Roman numerals for diatonic seventh chords shows the full set for major and minor, with audio. For the numerals themselves, see the functional harmony guide.
How do seventh chords resolve?
The seventh of the chord is a dissonance, and it has a job: it resolves down by step. In G7 to C, the F falls to E and the leading tone B rises to C. Those two notes, B and F, form a tritone, and their pull in opposite directions is what makes V7 sound like it has to go home.
The same rule holds for the other types. In B°7 to Cm, B rises to C while A♭ falls to G and F falls to E♭. In part-writing, check the seventh first, then look for the parallel fifths and octaves that tend to appear when four voices move at once.
How are seventh chords written in chord symbols?
Different books use different shorthand for the same chord. These are the ones you'll see most.
- Major seventh: Cmaj7, CM7, CΔ7.
- Dominant seventh: C7. A plain "7" always means major triad plus minor seventh.
- Minor seventh: Cm7, Cmin7, C–7.
- Half-diminished: Cø7 or Cm7♭5.
- Fully diminished: C°7 or Cdim7.
The most common slip is reading "C7" as a major seventh chord. It isn't: C7 has B♭. If the chord has B natural, the symbol needs "maj" or a triangle.
What does Michord show for seventh chords, and what doesn't it do?
In Michord you play the chord on a MIDI keyboard, the on-screen piano or your computer keyboard, and the app names what you played. With the subscription you get the chord symbol, the inversion and the Roman numeral in the current key.
- Play B–D–F–A in C major: the symbol reads Bm7b5 and the Roman numeral is viiø7.
- Lower the A to A♭: the symbol changes to Bdim7, the numeral to vii°7, and the chord is marked as borrowed from C minor.
- Play D–F♯–A–C in C major: Michord reads it as a secondary dominant, V7/V, with the note "Dominant of G — still in C".
That makes the one-note difference easy to test: hold three notes, move the fourth by a half step, and watch the name change. The analysis is rule-based, not AI. Michord doesn't listen to recordings or song files and doesn't read sheet music or photos. It's a desktop app for macOS (Apple Silicon) and Windows; there is no phone or tablet version.
How can you practise seventh chords in 15 minutes?
- Five types on one root (5 min). Play Cmaj7, C7, Cm7, Cø7 and C°7 in a row, saying which note you lowered. Repeat on F and G.
- Diatonic sevenths (5 min). Play the seven chords of C major up and down, naming type and Roman numeral. Then do G major.
- The one-note test (5 min). On B, D and F♯, play the half-diminished chord, then the fully diminished one. Sing the seventh both times.
If Michord is open, cover the screen, name the chord, then look. If you're working towards an exam, add this routine to the weekly plan in the music school audition preparation guide.
How can teachers present seventh chords in class?
Start from one triad and change one note at a time. Students hear five chord qualities appear from a single hand position, and the table above becomes something they've heard rather than something to memorise. With Michord on a shared screen, the symbol and Roman numeral update as you play, so the class sees ø7 turn into °7 at the moment the seventh drops. Screen recording with audio is part of the subscription if you want to keep the lesson.
Conclusion
A seventh chord is a triad plus a seventh, and its type comes from those two parts. Learn the five types on one root, then find them in a key: maj7 on I and IV, m7 on ii, iii and vi, a dominant seventh on V, a half-diminished on vii. When a diminished triad shows up with a fourth note, measure the seventh: minor means half-diminished, diminished means fully diminished.
To see the name of every chord you play, download Michord. The permanent free plan needs no credit card. Chord symbols, inversions and Roman numeral analysis come with the subscription: 2.99 USD per month or 22.99 USD per year.
Play a chord and see its symbol, inversion and Roman numeral. Free plan for macOS (Apple Silicon) and Windows with no credit card; chord analysis comes with the subscription (2.99 USD/month · 22.99 USD/year).
Download MichordFAQ
What is the difference between a half-diminished and a fully diminished seventh chord?
Both are built on a diminished triad. The half-diminished chord adds a minor seventh (B–D–F–A), the fully diminished chord adds a diminished seventh (B–D–F–A♭). The two chords are one note apart, and that note is a half step lower in the fully diminished chord.
Is m7♭5 the same as half-diminished?
Yes. Cm7♭5 and Cø7 are two names for the same four notes: C, E♭, G♭ and B♭. Jazz and pop charts usually write m7♭5; classical analysis usually writes ø7.
What are the five types of seventh chords?
Major seventh (Cmaj7: C–E–G–B), dominant seventh (C7: C–E–G–B♭), minor seventh (Cm7: C–E♭–G–B♭), half-diminished (Cø7: C–E♭–G♭–B♭) and fully diminished (C°7: C–E♭–G♭–B𝄫). Each is a triad plus a seventh above the root.
Which seventh chords are diatonic in a major key?
In C major: Cmaj7 (Imaj7), Dm7 (ii7), Em7 (iii7), Fmaj7 (IVmaj7), G7 (V7), Am7 (vi7) and Bø7 (viiø7). Every major key has the same pattern. The fully diminished seventh is not diatonic in major; it comes from the minor key.
Does C7 mean C major seventh?
No. C7 is the dominant seventh chord: C, E, G and B♭. C major seventh has B natural and is written Cmaj7, CM7 or CΔ7.
Does Michord name seventh chords, and is it free?
Michord names the chords you play on a MIDI keyboard, the on-screen piano or your computer keyboard. Chord symbols, inversions and Roman numeral analysis come with the subscription: 2.99 USD per month or 22.99 USD per year. The permanent free plan needs no credit card and includes all input methods, a real grand piano sound and the note names of the keys you press. The analysis is rule-based, and Michord does not listen to recordings.