Butterfly chords are chords characterised by central symmetry, obtained by the mirror conjunction of two epsilon chords. Their name derives from the fact that their structure evokes two wings arranged around a common axis.
Structure
Butterfly chords derive from the combination of an epsilon chord with its mirror chord, arranged in a complementary position beyond the octave. The result is a symmetrical structure in which the two sets of four notes face each other like two wings.
Since each epsilon chord extends up to a seventh, major or minor, the axis of symmetry is located between the seventh of the lower chord and the root of the upper chord. In this way the overall structure does not coincide with a single epsilon, but with a broader construction founded on the mirror reflection of two corresponding epsilon chords.
Principal Configurations
The principal configurations of butterfly chords are formed by two epsilon chords arranged one below and one above, with the upper chord placed one octave above the lower one. In the following table, both the lower chord and the upper chord are indicated starting from C.
Between the top note of the lower chord and the bottom note of the upper chord, a central interval is thus created that functions as the axis of the structure.
The perfectly symmetrical configurations are the following:
| Label | Lower chord | Upper chord | Structure |
|---|---|---|---|
| maj13 | C–D–G–B | C–E–A–B | 2 4 3 (2♭) 3 4 2 |
| maj13 | C–E–A–B | C–D–G–B | 3 4 2 (2♭) 2 4 3 |
| m13 | C–E♭–A♭–B♭ | C–D–G–B♭ | 3♭ 4 2 (2) 2 4 3♭ |
| m13 | C–D–G–B♭ | C–E♭–A♭–B♭ | 2 4 3♭ (2) 3♭ 4 2 |
| phryg | C–D♭–G–B♭ | C–E♭–A–B♭ | 2♭ 5♭ 3♭ (1) 3♭ 5♭ 2♭ |
The two maj13 and m13 configurations constitute the principal pairs of major and minor type. The phryg configuration represents a further variant, founded on a harsher and more concentrated symmetry.
Alongside these perfectly symmetrical forms, other combinations are also possible which, while preserving the same intervallic layout, modify the quality of the intervals (major/minor). In this way the principle of butterfly chords is not exhausted in the canonical configurations listed here, but opens onto a broader range of harmonic possibilities.
Related Entries
Epsilon Chord
Diatonic Interval Vector
Diatonic Class Vector