Accidental (music)

Accidental (music)

In music, an accidental is a note whose pitch (or pitch class) is not a member of a scale or mode indicated by the most recently applied key signature. In musical notation, the symbols used to mark such notes, sharps (♯), flats (♭), and naturals (♮), may also be called accidentals. An accidental sign raises or lowers the following note from its normal pitch ignoring sharps or flats in the key signature, usually by a semitone, although microtonal music may use "fractional" accidental signs, and one occasionally sees double sharps or flats, which raise or lower the indicated note by a whole tone. Accidentals apply within the measure and octave in which they appear, unless canceled by another accidental sign, or tied into a following measure.

...the first seven letters of the alphabet represent the basic diatonic pitches, with additional symbols called accidentals. In addition to the sharp (♯) and flat (♭) used in Europe to indicate the displacement of a scale degree by a semitone up or down, respectively, Arabic theorists have added accidentals representing a lowering of a pitch by a quarter-tone and raising it by a quarter-tone sharp . (Iranians use different symbols.) —Alves (2008)

The modern accidental signs derive from the round and square small letter b used in Gregorian chant manuscripts to signify the two pitches of B, the only note that could be altered. The round b became the flat sign, while the square b diverged into the sharp and natural signs.

Sometimes the black keys on a musical keyboard are called accidentals or sharps, and the white keys are called naturals.