Diminished Triad
Two minor thirds stacked on each other: C, E flat and G flat. The outer two notes are a tritone apart, and that is why this chord behaves like a question rather than a statement.
- 3 notes
- 1 b3 b5
- unstable
which styles use it
- Classical
- Jazz
- Film music
- Metal
Which notes are in a diminished triad?
A root, three half steps up, and three half steps up again. In C: C, E flat and G flat.
- C, the root
- E flat, the minor third
- G flat, the diminished fifth
Both gaps are the same size, and together they add up to six half steps. That distance is the tritone, and it is the single most restless interval in the system: it sits exactly halfway between the fourth and the fifth, so your ear cannot file it as either, and it splits the octave into two equal halves, so it points nowhere in particular.
Where does it want to go?
Up a half step, almost always. The diminished triad turns up on its own in a major key, on the seventh degree: in C that is B, D and F. The B is the leading note and leans up to C, the F leans down to E, and those two notes are exactly what gives C major its identity.
Play B, D and F and then C, E and G and you hear both moves happen at once. Play B, D and F on its own and leave it, and you hear how long a listener is willing to wait.
It shares three of its four notes with G7, which is why it does the same job on the cheap: you get the pull towards home without playing a full dominant.
Major, minor, diminished or augmented?
Four chords, the same three positions, and each one moves a single note. Play them back to back on the same root before you read the reasons.
- Major (C E G) - Four half steps then three. The blend is closest to the natural overtones, so this is the one that sounds finished.
- Minor (C Eb G) - Three then four, the stacking reversed. The fifth is still perfect, so it is every bit as stable as major, just darker.
- Diminished (C Eb Gb) - Three then three. The outer interval is now a tritone and the chord leans hard on whatever comes next.
- Augmented (C E G sharp) - Four then four. Every gap is identical, so no note can claim to be the root and the chord floats.
When do you reach for it?
- As the chord on the seventh degree, one step before you come home.
- As a passing chord between two chords a whole step apart, with the bass walking up through it.
- Anywhere you want one bar of genuine unease in an otherwise calm progression.
Common mistakes
- Ending a phrase on one
Your ear reads it as an unfinished sentence. If that is what you want, good. If not, give it somewhere to go.
- Confusing it with the diminished seventh
This one has three notes. Add a fourth another minor third above and you get dim7, which divides the octave into four equal parts and behaves differently.
Keep going
Everything in chords
- Major Triad
- Minor Triad
- Diminished Triad
- Augmented Triad