Diminished Chords on Piano

The diminished chord is a dissonant triad built from two minor thirds — creating a dark, tense, and unstable sound that demands resolution. It is used as a passing chord, a dramatic tension builder, and a key-change pivot in classical, jazz, and film music.

Formula: Root – Minor 3rd – Diminished 5th

Intervals: 3 + 3 semitones (two stacked minor thirds)

Scale degrees: 1–♭3–♭5

Sound: Tense, dark, unstable, dramatic

Symbol: dim or ° (Cdim, C° etc.)

Diminished vs Half-Diminished vs Diminished 7th: The diminished triad (1–♭3–♭5) is the foundation. Add a minor 7th and you get half-diminished (m7♭5). Add a diminished 7th and you get fully diminished 7th (dim7). Each has a different level of tension and function in harmony.