Fully Diminished

Diminished triad + diminished seventh; symmetrical, strong leading tendencies.

Fully Diminished Seventh Chord (dim7)

The Fully Diminished Seventh, notated dim7 or °7, is the most tense and unstable of all seventh chords.

It’s formed entirely of stacked minor thirds, creating perfect symmetry and giving it a unique, shape-shifting quality.

This chord doesn’t truly belong to one key — it can resolve in multiple directions, making it a powerful pivot in classical and jazz harmony alike.

Structure

Formula:

Root – Minor 3rd – Diminished 5th – Diminished 7th

Semitone steps from root: 0 – 3 – 6 – 9

Example (B°7):

B – D – F – A♭

Interval	Distance	Note	Function
Root	0	B	Tonal anchor (unstable)
Minor 3rd	+3	D	Adds minor darkness
Diminished 5th	+6	F	Core tritone tension
Diminished 7th	+9	A♭	Heightens instability and symmetry

Symmetry and Equivalence

Because it’s built entirely from minor thirds, the chord divides the octave into four equal parts.

That means there are only three unique diminished seventh chords in the chromatic system — each one can represent four enharmonic spellings.

For example:

B°7 = D°7 = F°7 = A♭°7 (all the same notes, just different roots).

This symmetry makes the chord enharmonically ambiguous, allowing composers to modulate to distant keys with elegant disguise.

Roman Numeral Function

Scale Degree	In Major Key	In Minor Key	Function
vii°7	Leading-tone chord	vii°7	Leads to tonic (I or i)
vii°7/V	Secondary diminished	–	Resolves to V
Passing	Chromatic connector	–	Links chords by semitone

In both major and minor, the vii°7 naturally resolves to I because the tritone inside the chord pulls outward by semitone in opposite directions.

Inversions

Inversion	Notes (B°7)	Symbol	Bass Note	Function
Root Position	B–D–F–A♭	B°7	B	Leading-tone tension
1st Inversion	D–F–A♭–B	B°7/D	D	Chromatic bass movement
2nd Inversion	F–A♭–B–D	B°7/F	F	Pivot harmony
3rd Inversion	A♭–B–D–F	B°7/A♭	A♭	Dark, ambiguous sound

Because of its symmetry, all inversions sound nearly identical — only the bass note changes the sense of direction.

Sound and Character

The dim7 chord is a favorite tool for composers seeking drama or modulation — from Bach to Chopin, Debussy to John Williams.

Common Progressions

Progression	Function	Example
vii°7 – I	Leading tone resolution	B°7 → C
vii°7/V – V	Secondary dominant setup	F#°7 → G7
i – vii°7 – i6	Chromatic voice leading in minor	Am – G#°7 – Am/C
I – #I°7 – ii	Passing diminished	C – C#°7 – Dm
ii°7 – V7 – I	Classical cadence in minor	B°7 – E7 – Am

Real-World Examples

Work	Composer / Artist	Usage
“Moonlight Sonata”	Beethoven	Leading-tone dim7s linking minor keys
“Prelude in E Minor”	Chopin	Chromatic dim7 voice leading
“Blue in Green”	Miles Davis	Dim7 pivot chords for tonal ambiguity
“Yesterday”	The Beatles	Passing diminished color
“Round Midnight”	Thelonious Monk	Dim7 reharmonizations in bridges

Application Tips

Summary

Attribute	Value
Formula	1 – ♭3 – ♭5 – ♭♭7
Semitones	0 – 3 – 6 – 9
Tonality	Fully dissonant
Emotional Color	Dark, tense, mysterious
Function	Leading-tone or dominant substitute
Inversions	Four (symmetrical)
Common Progressions	vii°7–I, passing dim7s, ii°7–V7–i
Used In	Classical, jazz, film, chromatic harmony