Accidental (music)

[citation needed] The modern accidental signs derive from the two forms of the lower-case letter b used in Gregorian chant manuscripts to signify the two pitches of B, the only note that could be altered.

According to Kurt Stone, the system is as follows:[1] Because seven of the twelve notes of the chromatic equal-tempered scale are naturals (the "white notes", A; B; C; D; E; F; and G on a piano keyboard) this system can significantly reduce the number of naturals required in a notated passage.

Thus, the effect of the accidental must be understood in relation to the "natural" meaning of the note's staff position.

[3] An F double sharp is a whole step above an F, making it enharmonically equivalent to a G. These alterations apply to the note as if it were a "natural", regardless of the key signature (see the F in measure 2 of the Chopin example below).

One such system for notating quarter tones, used by the Czech Alois Hába and other composers, is shown.

In the 19th and early 20th centuries, when Turkish musicians switched from their traditional notation systems—which were not staff-based—to the European staff-based system, they refined the European accidental system so they could notate Turkish scales that use intervals smaller than a tempered semitone.

The flat sign ♭ derives from a round b that signified the soft hexachord, hexachordum molle, particularly the presence of B♭.

In the High Middle Ages, a widespread musical tradition was based on the hexachord system defined by Guido of Arezzo.

A major problem with the system was that mutation from one hexachord to another could introduce intervals like the tritone that musicians of the time considered undesirable.

To avoid the dissonance, a practice called musica ficta arose from the late 12th century onward.

This introduced modifications of the hexachord, so that "false" or "feigned" notes could be sung, partly to avoid dissonance.

For example, when a semitone relationship is indicated between F and G, either by placing a mi-sign (♮) on F or a fa-sign (♭) on G, only the context can determine whether this means, in modern terms, F♯-G or F-G♭, or even F♭–G.

The implied alterations can have more than one solution, but sometimes the intended pitches can be found in lute tablatures where a fret is specified.

[11] The older practice continued in use well into the 18th century by many composers, notably Johann Sebastian Bach.