What Are the Enharmonic Key Signatures?

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

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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, keys like B-sharp and F-flat major are seemingly absent, while others go by two names. When comparing C-sharp major and D-flat major, it's easy to see these notes are exactly the same. 

  • 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

    One Scale, Two Names

    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.

    Notes and chords also have enharmonic equivalents. Technically (but not practically), each can go by an infinite amount of names. For example, E quadruple-flat could be another way of saying C. In practice, 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?

    So, why bother keeping around two key signatures if their scales are the same? Because it provides the option of writing a scale using either sharps or flats. Since it's best to use only one type of accidental in each composition, this option makes some key changes easier to compose and read.

    For example, if switching from the key of F# major to its fifth, C# major (which contain 6 and 7 sharps, respectively), it would be silly to confuse the eyes and opt for the 5-flatted Db major instead. There are, however, exceptions to this advice, especially when exploring modal scales.

    Enharmonic Key Signatures

    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