Enharmonic exchange
When you replace a note with its enharmonic, you are actually renaming (spelling) a note without sounding different (on a piano) (eg F# or Gb).
What you achieve with such enharmonization is the most 'logical' possible name in the musical context used. Each note (except G-sharp/A-flat) can thus be spelled in three ways:
| B# | C | (D♭♭) |
| (B##) | C# | D♭ |
| C## | D | (E♭♭) |
| D# | E♭ | (F♭♭) |
| (D##) | E | F♭ |
| E# | F | (G♭♭) |
| (E##) | F# | G♭ |
| F## | G | (A♭♭) |
| G# | A♭ | |
| (G#) | A | B♭♭ |
| A# | B♭ | (C♭♭) |
| (A##) | B | C♭ |
The first spelling is the preferred spelling in the key of C (in bold)
The scale of C is: C-D-E-F-G-A-B-C.
- Preferred: C#, E♭, F#, G#, B♭
- Alternative: D♭, D#, G♭, A♭, A# (italics)
You can make similar lists for each key.
C# scale: C#-D#-E#-F#-G#-A#-B#-C#
- Preferred: C##, E, F##, G##, B
- Alternative: D, D##, G, A, A##
and so on.
In theory, of course, even more complicated enharmonizations are conceivable (B♭♭♭ and F### as enharmonizations for the G#/A♭, but in music practice you will never encounter them. Usually you will find the double sharps or double flats rather enharmonized away making the music easier readable for the average player.
The first alternative spelling (and notation) is obtained after enharmonic exchange by <x>.
The second alternate spelling with <alt-shift-x>.
Thus, although most pitches can be written in three ways, most key changes will be rare (in C major it will be extremely unlikely to write the note C as B# or even more exceptionally as D♭♭). If a lot of enharmonization seems necessary, there will usually be a modulation or notation in the wrong key!
The chord symbols used with a melody can also give rise to enharmonization; once an Fm chord is played ( f - a♭ - c) you will not encounter any g# in the melody. You can also enharmonize the chord symbols themselves: an A♭ chord is much more logical in keys with, for example, flats than a G# chord.