Goal
Understand how to read key signatures and how to properly write them.
Key Signatures
Key signatures are a tool to make it so we don’t need to write sharps and flats all over the place every time. For example, in D major there are 2 sharps, F# and C#. If the whole song is in D major that will be a lot of sharps to write! Wouldn’t it be easier to just say “Hey, we are in D major so use the appropriate sharps and flats.” Then you can just write the notes that differ from D.
For example here is a piece in A major that has all the sharps written in:
Now here is a piece that uses the key signature of A:
See how much simpler that looks!
When choosing a key signature you pick it based on the natural minor or major scale. If you are using harmonic or melodic minor you use the natural minor key signature and use accidentals for those scales. The reason for this is the natural minor is the “base” version and the other scales are alterations to the base that are used from time to time for harmonic reasons.
Constructing Key Signatures
Key signatures have a specific order. Thankfully it is an order we have already covered. It is the order of flats for flat keys and sharps for sharp keys.
Flats appear in the order BEADGCF and sharps appear in the order of FCGDAEB. The spots they appear are standard and form rows that make them easy to identify for key signatures with many sharps or flats. Here is a chart showing them all:
 0 Sharps | None | C Major | A Minor | 0 Flats | None | C Major | A Minor |
 1 Sharps | F♯ | G Major | E Minor |  1 Flats | B♭ | F Major | D Minor |
 2 Sharps | C♯ | D Major | B Minor |  2 Flats | E♭ | B♭ Major | G Minor |
 3 Sharps | G♯ | A Major | F♯ Minor |  3 Flats | A♭ | E♭ Major | C Minor |
 4 Sharps | D♯ | E Major | C♯ Minor |  4 Flats | D♭ | A♭ Major | F Minor |
 5 Sharps | A♯ | B Major | G♯ Minor |  5 Flats | G♭ | D♭ Major | B♭ Minor |
 6 Sharps | E♯ | F♯ Major | D♯ Minor |  6 Flats | C♭ | G♭ Major | E♭ Minor |
 7 Sharps | B♯ | C♯ Major | A♯ Minor |  7 Flats | F♭ | C♭ Major | A♭ Minor |
Note that the key signature tells you merely about the number of sharps or the number of flats, it doesn’t tell you the key directly! This is because you could be major or minor. In order to determine the scale the piece is using, meaning the “key”, you will need to look at the key signature first as a clue to narrow down the possibilities and then you will need to look at the piece itself and see what notes are being used to finalize what scale is used!
For example, if a piece has a key signature of no flats and no sharps you may be quick to say its C major! But A major also has no flats or sharps! Therefore you must look at the piece. If you see a lot of minor chords in important positions then the piece is probably in A minor, but if you see C major chords in important positions then it's probably in C major. The moral of the story is the key signature doesn’t tell you the key! It just provides a clue!
Identify the possible key from key signatures
Each key signature suggests a possible major or minor key. To identify the key we can simply figure out how many sharps and flats there are and use the order of flats or sharps to figure out the possibilities. If you are unfamiliar with the order of flats and sharps in the use of scale construction please see method three of the major scale lesson.
Consider the following key signature and determine the possible keys:
Here we see two flats. Using the order of flats BEADGCF, moving from C twice in the direction of flats gives us the possible scale of Bb Major. Moving from A twice in the direction of flats gives us the possible scale of G minor. That is all the key signature can tell us. We would need to look at the notes to determine which is actually being used.
Example 2:
Here we see three sharps. Using the order of flats BEADGCF we move from C three times in the sharp direction. We see that A major is the first option. Doing the same thing but starting on A for natural minor we see that F# minor is the potential minor option.
Key signatures are a great way to convey your key, save us from writing flats and sharps all over and make accidentals meaningful because any accidental must be a deviation from the key, hence the name accidental.
Type your answer as ___ major or ___ minor. Example: C major.
To support this series please consider donating via
paypalor joining the
patreon.