Diminished Chords Explained

The diminished triad, and its two sevenths

Start with a minor triad and squeeze the fifth down a half step: C, Eb, Gb. That flat fifth is the tension. The triad is already restless, but the family gets more interesting when you add a fourth note. Stack yet another minor third and you reach the fully diminished 7th, Cdim7 = C Eb Gb A, four notes each a minor third apart, symmetric and very tense. Instead, keep the diminished triad but add an ordinary flat seventh and you get the half-diminished chord, written m7b5: Cm7b5 = C Eb Gb Bb, noticeably softer.

Those three, the triad, the dim7 and the half-diminished, are close cousins that sound and function differently, so it pays to hear them side by side.

Build any diminished chord

Toggle the type, pick a root, and watch the notes light up. Notice how the dim7 shape repeats every minor third.

Dim7 versus half-diminished

These two get confused because both start from a diminished triad, but they do different jobs. The fully diminished 7th is symmetric and maximally tense, four minor thirds around the circle, and like the augmented chord its symmetry means there are only three distinct dim7 chords in all of music. It usually works as a passing chord, sliding between two stable ones. The half-diminished chord (m7b5) is gentler and has a clear home: it is the ii chord of a minor key, the launch pad of a minor ii-V-i, so Dm7b5 to G7 to Cm is the minor-key cousin of the progression you meet with minor sevenths.

Diminished next to augmented

Diminished and augmented chords are mirror images. Augmented stacks major thirds and stretches the fifth sharp; diminished stacks minor thirds and squeezes the fifth flat. Both are symmetric, both sound unstable, and both are just one altered note away from triads you already know from chord training. Learn the pair together, the stretch and the squeeze, and neither feels foreign for long.

Practise diminished chords in the game

Open the game and play Level 5, which covers diminished chords, then add the dim7 and half-diminished types to a Custom pool. Play each on your MIDI keyboard or into your microphone and get told instantly whether the shape was right. Toggling between dim, dim7 and m7b5 trains the small differences that matter most. Free in the browser, nothing to install.

Common questions

What is a diminished chord?

A diminished chord is a minor triad with its fifth lowered a half step: root, minor third and flat fifth. In C that is C, Eb and Gb. Two stacked minor thirds give it a tense, anxious sound. Add another minor third and you get a diminished 7th; use a flat seventh instead and you get a half-diminished chord.

What is the difference between dim7 and half-diminished?

The seventh. A diminished 7th (Cdim7) stacks three minor thirds: C Eb Gb A, fully symmetric and very tense. A half-diminished chord, written m7b5 (Cm7b5), is a diminished triad with a normal flat seventh: C Eb Gb Bb, softer and the usual ii chord in a minor key.

Why are there only three diminished 7th chords?

Because the diminished 7th is fully symmetric: four notes each a minor third apart, dividing the octave evenly. Any note in the chord can be the root, so the 12 roots collapse into just three distinct diminished 7th chords, each covering four names.

How do I practise diminished chords?

Drill the triad, the dim7 and the half-diminished with instant feedback. In ChordRunner, Level 5 covers diminished chords, and the dim7 and half-diminished types are available too. Play each on a MIDI keyboard or through your microphone and get judged on the spot.