A key signature is a sign written at the beginning of each line of music which indicates the frequent use of accidentals, thus dispencing the need to write them throughout a piece.
Figure 1: A key signature after a treble clef.
The Circle of Fifths
A way of identifying key signatures and which accidentals belong to each key is to study the circle of fifths:
Figure 2: The glorious circle of fifths!
To identify how many sharps or flats belong to each key, simply count left or right from C:
Left: C = 0 flats, F = 1 flats, Bb = 2 flats, Eb = 3 flats, etc.
Right: C = 0 sharps, G = 1 sharps, D = 2 sharps, A = 3 sharps, etc.
To identify which sharps or flats belong to each key, count left or right from in-between Bb and F:
- For sharps you count right (F, C, G, D, A, E, B). A good mnemonic for remembering this order of sharps is Fat Cats Go Down Alleys Eating Birds.
- For flats you count left (B, E, A, D, G, C, F). A good mnemonic for remembering this order of flats is Battle Ends And Down Goes Charles' Father.
It should be noted that every major key has a relative minor key and vice versa. This is because they share the same set of diatonic notes, but each has a different tonic. The following table shows a list of relating keys:
|Major Key||Minor Key|
|C Major||A Minor|
|G Major||E Minor|
|D Major||B Minor|
|A Major||Gb Minor|
|E Major||Db Minor|
|B Major||Ab Minor|
|Gb Major||Eb Minor|
|Db Major||Bb Minor|
|Ab Major||F Minor|
|Eb Major||C Minor|
|Bb Major||G Minor|
|F Major||D Minor|
Another way to recognize a relative key from major to minor is to simply count a minor third descending; and from minor to major, a minor third ascending:
Figure 3: Counting a min. 3rd between two tonic chords.
There is no way to emphasize how important the cycle of fifths is and should be well studied until memorized.
Figure 4: A diagram of all key signatures.
Also see Accidentals | Lyrics.