Enharmonic Key Signatures

Learn Why Some Notes and Scales Go By Two (Or More) Names

Enharmonic scale equivalents.
( Click to enlarge) The scales of C# major and Db major . Sidney Llyn

If you’re familiar with the circle of fifths – or you just know your way around the key signatures – you may have noticed a few anomalies. For example, some keys, like B-sharp and F-flat major, are seemingly absent while others go by two names: If you compare the notes of both C-sharp major and D-flat major, you’ll realize that they are exactly the same. Observe:

  • C-sharp major: C#   D#    E#    F#   G#   A#   B#
  • D-flat major:     Db   Eb     F     Gb   Ab   Bb    C

Likewise, their respective relative minors are also identical in tone:

  • A-sharp minor: A#    B#   C#    D#    E#    F#    G#
  • B-flat minor:     Bb    C     Db    Eb     F     Gb    Ab

When scales are identical in this way, they’re known as enharmonic equivalents. This means that these scales are really just one scale going by two different names (see image).

Notes and chords also have enharmonic equivalents; and technically (but not practically), each can go by an infinite amount of names: E quadruple-flat could be another way of saying C (see picture #2). In practice, however, notes and scales rarely go by more than two names, and there are only six key signatures with enharmonic equivalents (see table, below).

What Is the Point of Enharmonic Key Signatures?

So, why bother keeping around two key signatures if their scales are the same anyway?

Because it gives you the option of writing a scale using either sharps or flats; and, since it's best to use only one type of accidental in a composition, this option makes certain key changes easier to compose and read.

For example, if you switch from the key of F# major to its fifth, C# major (which contain 6 and 7 sharps, respectively), it would be silly to confuse your eyes and opt for the 5-flatted Db major instead.

There are, however, exceptions to this advice, especially when exploring modal scales.

The Enharmonic Key Signatures Are:

Major / Relative Minor:No. of SharpsEnharmonic Key:No. of Flats
 
B major / G# minor5Cb major / Ab minor7
F# major / D# minor6Gb major / Eb minor6
C# major / A# minor7Db major / Bb minor5