Diminished

Notes and formula

The formula is 1 – ♭3 – ♭5, or 0 – 3 – 6 in semitones from the root: two minor thirds stacked on top of each other. C to E♭ is three semitones, E♭ to G♭ another three.

Everything about the chord follows from what is missing. Major and minor triads are held together by a perfect fifth; here that fifth is flattened, and the six-semitone gap left behind is the tritone — the one interval Western harmony has always treated as a question rather than a statement.

How to play it

On piano the chord is C–E♭–G♭, and the symmetry makes it easy to find: three keys up, three keys up again, counting black and white alike.

On guitar the bare triad is awkward, which is why it is rarely strummed. The workable form is x3454x, sounding C–G♭–C–E♭. In practice guitarists play the four-note diminished seventh instead, and most chord charts that print a ° mean exactly that.

Where it sits in a key

In a major key the diminished triad appears once, on the seventh degree — B–D–F in the key of C. Those are the top three notes of G7, which explains its behaviour completely: it is a dominant chord with the root removed, and it resolves to the tonic for the same reason G7 does.

In a natural minor key it lands on the second degree — D–F–A♭ in C minor — where it opens the same cadence from below. Either way the chord is a step on the way somewhere, not a place to stand.

How it is actually used

The everyday job of a diminished chord is to connect two chords a tone apart. Slide a diminished triad between them and the bass moves by semitone in both directions, which is why the sound turns up constantly in ragtime, in jazz standards and in Beatles verses without ever being the point of the bar.

It is almost never the destination. A phrase can pause on a major or minor chord indefinitely; a diminished chord held for more than a bar reads as suspense, and audiences hear it as a promise that something is about to happen.

Diminished, diminished seventh and half-diminished

Three different chords share the same triad, and chord charts confuse them constantly. Cdim is C–E♭–G♭. Cdim7 adds a diminished seventh — B♭♭, which sounds as A — and divides the octave into four equal parts. Cm7♭5, the half-diminished, adds a plain B♭ instead.

The practical difference is where each one goes. The diminished seventh passes; the half-diminished is a resting chord in minor keys, the ii of a minor ii–V–i. Reading ° as either one is the most common mistake in written jazz.

Scales that contain it

Locrian, the seventh mode of the major scale, is the only mode of that scale that fits the chord without alteration. Over a passing diminished chord players more often use the whole–half diminished scale, whose symmetry matches the chord's own.

Because the triad repeats itself every three semitones, any scale choice applies at three other roots as well. That is a shortcut worth knowing: learn one shape and it covers four chords.

Frequently asked questions