Key Signature

The ACCIDENTALS at the beginning of a composition (and each succeeding staff) which indicate the overall key of a piece. There are 12 different MAJOR keys and 12 MINOR, identified by the number of sharps or flats in the key signature.

Key signatures of seven sharps are not infrequent. A famous example is the third fugue in C-sharp major in the first book of JOHANN SEBASTIAN BACH'S WELL-TEMPERED CLAVIER. An example of seven flats in the key signature is the opening of IGOR STRAVINSKY'S THE FIREBIRD.

Changes of key signature in the course of a composition are common, but they are not made for each passing MODULATION. Even the extensive exposition of the second SUBJECT in a SONATA FORM movement, usually in the DOMINANT key, never warrants a change of key signature. However, in works not bound by a strict key relationship, in which tonalities range far and wide, composers often prefer to signalize a modulation by changing the key signature. The score of GUSTAV MAHLER'S Sixth Symphony includes episodes in every major and minor key, each carrying an appropriate key signature.

Key signatures are meaningless in 20th century ATONAL music. But as the atonal movement has waned, the key signature has made a strong comeback.

Relative major and minor keys are those having the same key signature. The customary raised seventh (leading tone) in a minor key is marked by an accidental, as a G♯ in the key of A minor, or an F double-sharp in the key of G-sharp minor. In key signatures loaded with flats, the raised seventh in a minor key is the cancellation of the corresponding flat, becoming a natural, e.g., D♮ in E-flat minor. Attempts have been made by modern composers, among them BÉLA BARTÓK, to add accidentals in the key signature. A piece in G minor would then carry the mandatory two flats but also the extra F#.