Keys and key signatures
What a key is, how to read a key signature, and how the circle of fifths organises the twelve major and minor keys.
Applied
Content under musical review. It may contain inaccuracies.
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What a key is, how to read a key signature, and how the circle of fifths organises the twelve major and minor keys.
Applied
A key is a scale with a centre: a tonic that acts as "home" and a set of chords organised around it. Saying a piece is "in D major" means its material comes from the D major scale and everything tends to return to D. The key signature summarises that scale's accidentals at the start of the staff.
Two major scales that sit next to each other on the circle of fifths. G major has one sharp; D major, two:
And a key with a flat, F major:
The circle of fifths puts the keys in order: clockwise, each key is a fifth higher and adds a sharp; anticlockwise, a fifth lower and adds a flat. Inside, each key's relative minor:
C major (0)
C major
I C · ii Dm · iii Em · IV F · V G · vi Am · vii° Bdim
Press a key to see its diatonic chords. Neighbouring keys share almost all their notes.
| Accidentals | Major | Relative minor | Altered notes |
|---|---|---|---|
| 0 | C | A | none |
| 1 # | G | E | F♯ |
| 2 # | D | B | F♯ C♯ |
| 3 # | A | F♯ | + G♯ |
| 4 # | E | C♯ | + D♯ |
| 5 # | B | G♯ | + A♯ |
| 6 # | F♯ | D♯ | + E♯ |
| 1 b | F | D | B♭ |
| 2 b | B♭ | G | B♭ E♭ |
| 3 b | E♭ | C | + A♭ |
| 4 b | A♭ | F | + D♭ |
| 5 b | D♭ | B♭ | + G♭ |
| 6 b | G♭ | E♭ | + C♭ |
Click a key on the circle and see which chords it contains and what its relative is:
D major in the harmony labThe order of sharps is always F♯ C♯ G♯ D♯ A♯ E♯ B♯, and the order of flats is the reverse: B♭ E♭ A♭ D♭ G♭ C♭ F♭. Two shortcuts for reading a signature:
Each signature serves two keys, the major and its relative minor. To decide which, look at the first and last chords, and look for the minor key's leading tone: in E minor you'll often see D♯ in the dominant, B7.
For guitarists, sharp keys (E, A, D, G) make good use of open strings; in flat keys many players reach for barre chords or a capo.
Neighbouring keys on the circle share six of their seven notes. That's why moves to the dominant (one step clockwise), the subdominant (one step anticlockwise) or the relative key are the smoothest. These are the closely related keys, the natural destinations for a modulation.
G major and its neighboursAt the bottom of the circle the keys overlap: F sharp major (six sharps) and G flat major (six flats) sound the same; so do B major and C flat major, and C sharp and D flat. The choice depends on context and readability: you pick the spelling with fewer accidentals or the one that fits the piece's neighbouring keys.
Beyond seven accidentals you get theoretical keys, such as G sharp major, which would need F𝄪 (a double sharp). In practice they're written as their enharmonic, A flat major.