Diminished triad on B play (help·info).

Dominant seventh and incomplete dominant seventh in C major: G7 and b^o chords Play (help·info).

A diminished triad chord ( Play (help·info)) is a triad consisting of a minor third and a diminished fifth above the root — if built on C, a diminished chord would have a C, an E♭ and a G♭^[1]. It resembles a minor triad with a lowered (flattened) fifth.

Diminished triad on C play (help·info).

ii^o6 in C minor play (help·info): first inversion d^o chord.

In the common practice period, the diminished chord is considered dissonant, or unstable. It lacks tonal center or drive because the diminished fifth symmetrically divides the octave.

A diminished chord occurs in a major scale only on the seventh scale degree; in the key of C, this is a B diminished chord (B, D, F). This also occurs in the seventh chord built on the fifth note; in C, this is G dominant seventh (G, B, D, F).

In a twelve-tone equal tempered tuning, a diminished chord has 3 semitones between the third and fifth, 3 between the root and third, and 6 between the root and fifth. It is represented by the integer notation {0, 3, 6}.

In most sheet music books, Cdim or C° denotes a diminished seventh chord (a four note chord) with root C, and Cm-5 or Cmb5 denotes a diminished triad with root C. However, in some modern jazz books and some music theory literature, Cdim or C° denotes a diminished triad, while Cdim7 or C°7 denotes a diminished seventh chord.

The ii^o6 chord is usually found in first inversion since it is diminished with the bass note doubled since it is not a part of the tritone, while the vii^o7 chord appears with all four factors most often in root position^[2]. In both cases resolve the bass up and move the upper voices downwards in contrary motion^[2]. The popular music symbol for a diminished triad is a capital letter designating the root (as with a major chord) with MI^(♭5) added^[3].

Diminished chord table

Chord	Root	Minor Third	Diminished Fifth
Cdim	C	E♭	G♭
C♯dim	C♯	E	G
D♭dim	D♭	F♭ (E)	A (G)
Ddim	D	F	A♭
D♯dim	D♯	F♯	A
E♭dim	E♭	G♭	B (A)
Edim	E	G	B♭
Fdim	F	A♭	C♭ (B)
F♯dim	F♯	A	C
G♭dim	G♭	B (A)	D (C)
Gdim	G	B♭	D♭
G♯dim	G♯	B	D
A♭dim	A♭	C♭ (B)	E (D)
Adim	A	C	E♭
A♯dim	A♯	C♯	E
B♭dim	B♭	D♭	F♭ (E)
Bdim	B	D	F

See also

• Half-diminished seventh chord
• Secondary leading-tone chord

Sources

1. ^ Benward & Saker (2003). Music: In Theory and Practice, Vol. I, p.68. Seventh Edition. ISBN 978-0-07-294262-0.
2. ^ ^{a b} Benward & Saker (2009). Music in Theory and Practice: Volume II, p.76. Eighth Edition. ISBN 978-0-07-310188-0.
3. ^ Benward & Saker (2003), p.77.