A key is a reference to music written in one of
twenty-four diatonic scales. There are twelve major scales and twelve minor scales. The
key signature indicates which of these major or minor scales the music is written. The
final cadence determines whether the key is major or minor. Key signatures are marked over
again at the beginning of each new staff system.
The key signature affects the pitch for the entire piece unless it is canceled and replaced with
another key signature. If a key signature is changed, the new signature appear on the
right side of the bar line. It is common to use naturals in order
to cancel all the sharps or flats from
the previous key signature before replacing it with the new key signature.
A sharp sign will have
the pitch of a note raised a half step for the entire piece. It
may be lowered at anytime with the use of a natural sign. Likewise, the flat sign will have the pitch of a note
lowered a half step for the entire piece. It may be raise at anytime with the use of a
natural sign. The natural sign lasts only for the duration of the measure.
In the ninth century, music was written in one of two keys; the key of C and the key of F. The key was determined by a clef symbol; the C clef and the F clef. A flat sign is normally placed at the beginning of each staff to indicate that the pitch B is lowered a half step for the entire piece. Accidentals, with the rare exceptions, were not used until the fourteenth century. After the mid fifteenth century, tuning systems have changed to accommodate composers willing to explore other keys. Various diatonic scales have been more accessible and marked with a key signature. After equal temperament had been developed in the sixteenth century, all keys were accessible to composers with greater ease.