You may not know what to do the first time you encounter a double sharp or a double flat in the wild!
Don’t panic! In this post, we’ll talk about what double sharps and double flats are and where they come from to help make your encounters with them more bearable. At first, they may seem unnecessary or redundant—why write an A double sharp when you could write a B?
By the end of this post, you’ll see the method behind the apparent madness of double sharps and flats and perhaps even come to appreciate the intricate key signature system for all its beauty (and quirks).
We’ll review the history of music notation and the key signatures to help you understand music theory better and discuss some practical situations where you might encounter double sharps and double flat notes.
But, before we dive into that…
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Table of Contents
A (Very Brief) History Of Music Notation
Before diving into the double sharp symbol’s meaning, it’s important to understand the musical context from which they emerged. After all, you wouldn’t have double sharps and double flats without having regular sharps and flats first or key signatures, for that matter.
We’re about to walk through a music theory minefield, so helmets on!
We can trace our Western music theory system back to Ancient Greece (it’s where the modes of the major scale get their name). However, what we’d begin to recognize as staves, notes, clefs, and music symbols wouldn’t be recognizable until the Middle Ages.
For more on the modes, check out our guide to modes in music.
Modern music theory, including modern notation and the concept of key signatures, evolved from the systems that baroque and classical musicians formalized a few centuries ago. Before then, music notation existed, but there wasn’t one unified way to represent the nuances of changing pitches and shifting tonal centers.
Regional varieties of notation worked well enough in their specific areas, but for one musician from Spain to operate well in a different musical region like Eastern Germany, they’d need to learn the specific nuances that made each region’s notation distinct. Essentially, it was a chaotic mess!
If you think learning to read music is hard enough today, try learning ten different notation systems!
The Key Signature
By the classical period, key signatures were the norm. A key signature is a set of sharp or flat symbols placed together on the staff at the beginning of a piece of music, after the clef but before the time signature.
For a music reader or a person hand-copying manuscripts in the 18th century, key signatures saved time and visually decluttered the staff. Using key signatures, you don’t need to write in sharps or flats when working with sharp or flat keys.
To demonstrate, here is a musical phrase written without a key signature followed by the same musical phrase written with a key signature.
The phrase is in the key of A major, which has three sharps (F#, C#, G#):
Without Key Signature:
Notice how the sharp accidentals clutter up the staff.
With Key Signature:
When using a key signature, you don’t need to fill the staff with accidentals because the notes marked as sharp or flat in the key signature are consistently sharp or flat throughout.
However, the primary musical function of key signatures is to organize the major scale formula across all twelve notes in an octave.
12 Notes But 15 Keys!?!
In Western music, there are twelve pitches in an octave. These twelve pitches are each a half step apart. You can apply the major scale formula to each of these twelve pitches to create twelve unique major scales.
Chromatic Scale with Sharps Ascending and Flats Descending:
Each of these pitches can be the starting point or tonic of the major scale formula.
You may be thinking, “I know the circle of fifths (or fourths for us jazz heads), and there are fifteen major keys and fifteen minor keys, not twelve!”
And you are right. Theoretically, there are fifteen major and minor keys. However, sonically, there are only twelve. Look at the image below, and you’ll see six enharmonic keys (the ones that overlap in the circle). These keys contain enharmonic notes, which are equivalent in pitch but not in name!
You’ll notice that three pairs of keys overlap on the circle. These pairs are sonically equivalent but have different key signatures and are considered other keys.
- C# and Db
- F# and Gb
- B and Cb
C# Major (A# relative minor) vs. Db Major (Bb relative minor):
F# Major (D# relative minor) vs. Gb Major (Eb relative minor):
B Major (G# relative minor) vs. Cb Major (Ab relative minor)
We start to see the double sharp and flat signs emerge when writing in these enharmonic keys.
BEFORE YOU CONTINUE...
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Finally! The Double Sharp and Flat!
After a long tour through music theory, we’ve made it to the point of this article—the double sharp and flat!
The key signature system is all about organization. When organizing the pitches of the major scale, each pitch has an important role or function. For example, each pitch can be the root of a diatonic triad or seventh chord.
When spelling out musical phrases that temporarily break this system, we use accidentals to notate the pitches outside of the key signature. When dealing with mostly sharp or flat notes, you need to maintain consistency and do your best to keep true to the organizational structure.
But what do the double sharp and flat signs look like?
Double Sharp Symbol
The double sharp symbol resembles a bold letter x. Instead of raising the pitch by one half step, you raise it by two half steps (this makes sense—it’s double sharp, after all).
Here is an A double sharp, which is enharmonically equivalent to B natural:
Double Flat Symbol
The double flat symbol looks like two flat symbols squished together. Instead of lowering the pitch by one half step, you lower the pitch by two half steps.
Here is an A double flat, which is enharmonically equivalent to G natural:
Accidentals in Action
Here is a basic ii-V-I progression in C major. Notice the accidental Ab, which is the b9 in the G7b9 chord:
What happens when we play this line in a flat or sharp key? This is where the double sharp sign and the double flat sign come into play.
Here is the same ii-V-I line transposed into the key of Cb:
Essentially, everything is already flat! When it comes time to play the b9 on the Gb7b9 chord, using an Abb rather than a G natural sign makes the most sense. Though a G natural is sonically correct, it isn’t technically a “9” in terms of the scale degrees. It’s a #1, which is weirder to look at.
So, there are two main reasons why a composer might use a double sharp or flat.
- Readability: Using double accidentals instead of enharmonic notes in certain situations looks cleaner.
- Maintain Tonal Organization: Double accidentals are necessary for certain scales and chords to keep the harmonic structure intact.
Let’s look at a few more examples.
The Double Sharp and Flat in Sheet Music
Usually, for scores, sheet music, and manuscripts, you’ll see these accidentals used to make things easier to read. Here are two examples:
1. Double Sharp in Claude Debussy’s The Engulfed Cathedral, Piano Prelude Book 1, No. 10:
Debussy uses an F double sharp here instead of a G natural. Though the pitch is enharmonically equivalent to a G natural, Debussy chose the F double sharp sign in this context.
This particular chord starts a series of descending chromatic parallel 7th chords. Perhaps he chose the F double sharp because it looks cleaner to see stacked thirds in the context of the parallel 7th chords that follow. You’ll notice a G natural used later on.
Debussy prioritized readability here, using a double sharp to keep the sheet music organized and making it easier to read.
2. Double Flats in Claude Debussy’s String Quartet Op. 10, 1893; Third Movement Opening:
In this piece, Debussy uses double flats (Bbb and Ebb) for similar reasons to the first example—it makes the piece easier to read. The voices in this piece are mostly descending. Moving from Bb to Bbb is visually cleaner than moving to an A natural. The same is true for the Eb that moves to Ebb rather than D natural.
The Double Sharp and Flat in Scales
Scales in certain keys will also use the double sharp or flat to maintain proper scale degrees. Certain scales, like the harmonic minor scale, must use double sharps or flats to keep the scale degrees consistent.
Though the seventh scale degree is sonically a D natural, we must call it a C double sharp to maintain the proper scale degrees.
Otherwise, it would look weirder:
- [D#-E#-F#-G#-A#-B-D-D#] instead of [D#-E#-F#-G#-A#-B-Cx-D#]
In cases like this, you are likelier to see Eb harmonic minor.
Here is another example of when you might see a double sharp sign. In the key of C#, every note is already sharp. If we were to play a C# Lydian scale, we’d need to raise the 4th scale degree by one half step.
Sonically, this would be a G natural. However, we need to use some 4th to label the fourth scale degree. Therefore, we must use an F double sharp to maintain the scale degrees. Otherwise, the scale would be spelled like this:
- [C#-D#-E#-G-G#-A-B#-C#] instead of [C#-D#-E#-Fx-G#-A-B#-C#]
The Double Sharp and Flat in Chords
You’ll also encounter double sharp and flat notes in chords for the very same reason you find them in scales—it’s all about maintaining proper scale degrees (and sometimes, it’s to improve readability like in the Debussy examples above).
Let’s use chords built from the scale examples above to demonstrate.
D#-(maj7) uses a double sharp:
C#maj7#11 has a double sharp:
Hopefully, this article has helped you understand why double sharps and flats exist in music! Here are a few points to sum up:
- The double sharp symbol alters a pitch by raising it by two half steps (or one whole step).
- The double flat symbol alters a pitch by lowering it by two half steps (or one whole step).
- Double sharps and flats are useful when the composer wants to preserve scale degrees in chords and melodies.
- Double sharps and flats usually appear in keys with a bunch of sharps or flats.
- Additionally, they will be used to make a music passage easier to read, like the double sharp used at the beginning of the series of parallel chords in the Debussy piece above.
Want To Master Jazz Theory and Improve Your Jazz Chops? Check out the Learn Jazz Standards Inner Circle!
Do you want to make serious progress in your jazz playing and jazz theory knowledge? If you are ready to overhaul your practice routine and learn jazz so that it sticks, you need to check out the Learn Jazz Standards Inner Circle.
The Inner Circle offers members an incredible treasure trove of jazz resources—including masterclasses, workshops, videos, and many courses, all designed to help you break through playing plateaus and see real, measurable progress.
Ready to take your playing to the next level? Come see what the Inner Circle has to offer!
