The sign, or no. of signs, written at the beginning of each staff, to indicate the key of the comp. Use of a key‐signature dispenses with the need to write accidentals (sharps or flats) for the notes affected throughout the comp. The keys of C major and A minor require no accidentals. The ‘natural’ form of the minor scale determines key‐signature. Major and minor key‐signatures are indicated thus:
The white note in each case represents the major key, the black note the minor key with the same signature (called ‘relative minor’).
Starting from C, the keynotes of the sharp keys rise 5 notes (a perfect 5th) each remove, and the keynotes of the flat keys fall 5 notes (a perfect 5th) each remove. In the sharp major keys the keynote is immediately above the last sharp.
In the flat major keys the keynote is 4 notes below the last flat (i.e. is at the pitch of the last flat but one in the signature).
Three notes down any major scale is the keynote of its relative minor or, conversely, 3 notes up any minor scale is the keynote of its relative major.
Keys with 6 sharps (F♯ major and D♯ minor) are (on kbd. instr.) the equivalents of the keys with 6 flats (G♭ major and E♭ minor), and keys with 7 sharps (C♯ major and A♯ minor) are the equivalents of the keys with 5 flats (D♭ major and B♭ minor). Composers use either one or the other of these signatures, but it is much easier to write in D♭ with 5 flats than in C♯ with 7 sharps.
The order of the sharps in the signatures is by rising 5ths, and the order of the flats by falling 5ths. Sharps—F C G D A E B—FlatsThus, one order is the other reversed.