Definition
Two notes are enharmonic when in equal temperament they have the same pitch but a different name: C# = Db, E# = F, B# = C, F## = G, Bbb = A. Enharmony extends to intervals, scales, keys and chords. The sound is the same, the function is not: the name tells you where the note comes from and where it tends to go.
Enharmonic notes
Every piano key has two or three possible names: C = B# = Dbb; C# = Db = B##; D = C## = Ebb, and so on (G#/Ab has only two names: G#, Ab). Spelling rule: one letter per degree in heptatonic scales (see Accidentals). In A major the third is C#, not Db; in F minor the sixth is Db, not C#.
Enharmonic intervals
| Semitones | Interval 1 | Interval 2 |
|---|---|---|
| 3 | Minor 3rd (C–Eb) | Augmented 2nd (C–D#) |
| 6 | Augmented 4th (C–F#) | Diminished 5th (C–Gb) |
| 8 | Minor 6th (C–Ab) | Augmented 5th (C–G#) |
| 9 | Major 6th (C–A) | Diminished 7th (C–Bbb) |
| 10 | Minor 7th (C–Bb) | Augmented 6th (C–A#) |
The sound is the same, the tendency is not: the augmented 2nd of harmonic minor (F–G# in A minor) pushes G# toward A; the minor 3rd F–Ab is stable. The augmented 6th (Ab–F#) opens out to the octave on G, the minor 7th (Ab–Gb) closes in toward the 6th.
Enharmonic keys
Three pairs of major keys coincide: B = Cb (5# / 7b), F# = Gb (6# / 6b), C# = Db (7# / 5b). In minor: G# = Ab, D# = Eb, A# = Bb. You choose the spelling with fewer accidentals or the one that is more consistent with the neighboring keys in the piece.
Enharmonic chords (the heart of modulation)
- Diminished seventh: B–D–F–Ab can be rewritten as D–F–Ab–Cb, F–Ab–Cb–Ebb, G#–B–D–F. It is the leading-tone chord of four different keys (C, Eb, Gb/F#, A): a perfect pivot for modulating (see the card on the diminished seventh chord).
- German augmented sixth = dominant seventh: in C minor the Ger+6 Ab–C–Eb–F# sounds like Ab7 (Ab–C–Eb–Gb), the dominant of Db. By reinterpreting it you modulate by a semitone.
- Augmented triad: C–E–G# = E–G#–B# = Ab–C–E: three keys with the same augmented dominant.
- Tritone substitution: G7 (G–B–D–F) and Db7 (Db–F–Ab–Cb) share the tritone B/Cb–F.
Examples in real songs
- Chopin, Prelude Op. 28 No. 15 “Raindrop”: it is in Db major, but the middle section moves to C# minor (the enharmonic of the parallel minor, which written in flats would require 8 flats). The repeated note Ab becomes G#: same sound, new dominant function.
- Debussy, “Clair de lune”: written in Db major (5 flats) instead of C# major (7 sharps), for readability.
- In pop and jazz, semitone modulations “via the German sixth” are frequent in final choruses with a key change.
Enharmony in the DAW
DAWs do not distinguish enharmony: in the FL Studio Piano roll C# and Db are the same key. When you export MIDI to a score, the software guesses the spelling: always check and rewrite (in MuseScore with J). A typical mistake: an Fm with Ab written as G# makes the part unreadable for a musician.
Outside equal temperament
In Pythagorean and meantone systems enharmonic notes do not coincide (in meantone G# is lower than Ab by about 41 cents). Strings and voices, free to tune, often differentiate enharmonic notes according to function.
Exercise
- Write the diminished seventh B–D–F–Ab in its four spellings and resolve each to its relative tonic (C, Eb, F#, A major or minor).
- In a project in C minor, insert Ab7 before a G7 (German sixth), then use the same Ab7 to go to Db: hear the double function.
- Rewrite the spelling of the melodic line of one of your songs in F minor and in D major without ever using the wrong name.
Related topics
Accidentals; Key signatures; The diminished seventh chord and its uses; Augmented sixth chords; Modulation techniques.