KEY SIGNATURE

The key signature represents the set of 7 notes, distributed across different octaves, chosen for a piece. This set is indicated at the beginning of the staff and follows a diatonic organization: each note name can appear only once.

In the case of C MAJOR, the set coincides with the natural notes (C, D, E, F, G, A, B), so there is no need to specify any alteration after the clef.

If, for example, we find a sharp on the F line, it means that we will use the altered note F# throughout the piece, until further indication. In this case, the set of notes will be: C, D, E, F♯, G, A, B. This set corresponds, for example, to the scale of G MAJOR, its relative E MINOR, and five other corresponding modes.

Based on the key signature, we can narrow down the possible tonal or modal frameworks of the piece and choose the appropriate scale among these seven options.

ORDER

The alterations in the key signature follow a precise order. In the case of sharps, the first alteration is F#, then the others are added by following the interval of a fifth above the previous note.

In the case of flats, the first alteration is B♭, and the others are added by following a chain of ascending fourths.

LIMITS

Although different key signatures allow us to explore major, minor, modal, and more reduced scales such as pentatonic ones, some scales cannot be fully expressed through a key signature. Even the harmonic and melodic minor scales cannot be completely represented by a single key signature, as well as various useful scales, from the whole-tone scale to many non-Western (ethnic) scales.

PLAYING OUTSIDE

Given these limitations, it is not always possible to develop a fully free and varied musical discourse within a single key signature. Therefore, playing notes outside the key signature is neither rare nor forbidden. The scales suggested by the key signature are not mandatory; rather, they help us infer the strongest center of gravity in the piece, often corresponding to the note where the music resolves.

IGNORING THE KEY SIGNATURE

Until the 17th century, alterations were often written as accidentals directly on the notes, even in clearly tonal music. Today, especially in contexts that move away from traditional tonality and use note sets that are neither strictly tonal nor modal, composers often omit the key signature altogether in favor of explicit accidentals, allowing for greater flexibility in pitch organization.