A Diminished Triad

Chord Tones: A Diminished Triad

Symbol: dim, ° — Formula: 1-♭3-♭5

Chord Notation

Roman numeral (e.g. I, IV, V) and Nashville Number notation are key-dependent. See Keys pages for chord function within specific keys.

Inversions

Harmonic Function

The A diminished chord commonly functions as the submediant (vi) in C major or dominant (V) in D major. Its harmonic role varies by key — in major keys it provides stable harmonic grounding.

The diminished triad features a flat third and flat fifth, creating a tense, unstable sound. It occurs naturally on the seventh degree of the major scale and resolves strongly to the tonic. The A Diminished Triad specifically contains 3 notes: A, C, D♯ (formula: 1-♭3-♭5). On guitar, A-rooted chords anchor to the open A string (5th string), and barre chord shapes rooted on A form the basis of the "A-shape" CAGED system. Blues, rock, and country music use A-rooted chords extensively — the classic 12-bar blues often starts on A, and many rock power chord riffs center on the open A string.

Common Progressions

The A Diminished Triad frequently appears in these progression patterns (shown in Roman numeral notation relative to key):

• viidim-I
• iidim-V

Songs Featuring the Diminished Triad

Well-known songs where the A Diminished Triad — or this chord type — plays a prominent role:

• Whole Lotta Love – Led Zeppelin (bridge)
• Killing Me Softly – Roberta Flack
• Black Magic Woman – Santana

Tuning Frequencies Across Temperaments

Frequencies shown at A=440 Hz. View full temperament data for any note.

Scales Containing the A Diminished Triad

These scales include the A Diminished Triad as a diatonic or characteristic chord: