In this lesson
A key signature sets the regular sharps or flats for a passage. At the start of a piece it appears after the clef and before the time signature. It saves repeating those signs beside every affected note.
If these symbols are unfamiliar, first read steps, tones and accidentals.
Read the altered note names
A sharp or flat in a key signature applies to that letter in every octave on the staff. One F♯ in the signature makes all Fs sharp by default, including Fs on other lines, spaces and ledger lines.
The signature continues across bar lines until it is replaced. A local accidental can temporarily override it. For example, in G major, F♮ changes that F to natural and normally affects later Fs at the same octave in that bar. In the next bar, separately played Fs return to the signature’s F♯ unless altered again. A tied continuation keeps its existing pitch.
Read the labelled pitches: F4, F4, F♯5, G4 in bar 1, then F♯4, G4, A4, B4 in bar 2. The F5 in bar 1 stays sharp because it is in a different octave from the local natural. Each bar contains four quarter notes. These are written pitches, with middle C labelled C4; conventional guitar notation sounds one octave lower.
The order of sharps and flats
Conventional major and minor key signatures use one type of sign in a fixed order:
- Sharps: F♯, C♯, G♯, D♯, A♯, E♯, B♯.
- Flats: B♭, E♭, A♭, D♭, G♭, C♭, F♭.
Use the first signs in the relevant list. Two sharps are F♯ and C♯; four are F♯, C♯, G♯ and D♯. Three flats are B♭, E♭ and A♭. Their signature order stays the same regardless of which note appears first in the melody.
The diagram shows all seven signs in each order. The line or space used to draw each sign depends on the clef, so identify its letter from the clef as well as counting the signs.
E major and C minor examples
E major uses F♯, C♯, G♯ and D♯ in its key signature. Its scale is E, F♯, G♯, A, B, C♯, D♯, E. Although you encounter F♯, G♯, C♯ and D♯ in that ascending scale, the signature keeps the order F♯, C♯, G♯, D♯.
C minor uses the signature B♭, E♭ and A♭. The natural-minor scale is C, D, E♭, F, G, A♭, B♭, C. Its raised seventh in harmonic minor is B natural, written as a local accidental. The basic C-minor key signature still has three flats.
Compare the major-scale and minor-scale lessons for their step patterns.
Use the circle of fifths for a visual key-signature map. Count clockwise for sharp major keys or counterclockwise for flat major keys, then take the signs in their fixed order.
Finding the major key
For a sharp signature, go a semitone above its last sharp to find the major tonic. With two sharps, the last is C♯, and the major key is D major.
For a signature with at least two flats, the second-to-last flat names the major tonic. With three flats, that note is E♭, giving E♭ major. Memorise the exceptions: no signs gives C major’s signature; one flat, B♭, gives F major’s.
Major and relative minor
A major key and its relative minor share a key signature. The relative minor’s tonic is degree 6 of the major scale, or three semitones below the major tonic.
| Sharps | Major key | Relative minor |
|---|---|---|
| 0 | C major | A minor |
| 1 | G major | E minor |
| 2 | D major | B minor |
| 3 | A major | F♯ minor |
| 4 | E major | C♯ minor |
| 5 | B major | G♯ minor |
| 6 | F♯ major | D♯ minor |
| 7 | C♯ major | A♯ minor |
| Flats | Major key | Relative minor |
|---|---|---|
| 1 | F major | D minor |
| 2 | B♭ major | G minor |
| 3 | E♭ major | C minor |
| 4 | A♭ major | F minor |
| 5 | D♭ major | B♭ minor |
| 6 | G♭ major | E♭ minor |
| 7 | C♭ major | A♭ minor |
Three flats could therefore belong to E♭ major or C minor. Look at how the melody and harmony establish the tonic; the signature alone does not distinguish them. Signatures can also appear in modal music.
Do not confuse relative keys with parallel keys. C major and A minor are relative and share a signature. C major and C minor are parallel: they share a tonic but have different signatures.
Compare relative and parallel minor on guitar to connect these definitions with a one-string calculation and open-chord shapes.
To practise, name the altered letters in a four-sharp signature before reading the notes. Then find its major and relative minor: E major and C♯ minor. The scale-degrees lesson explains how tonic and degree 6 relate.
References: Open Music Theory’s major scales and key signatures and the Open University’s relative major and minor keys.