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, 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 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.
Standard use of accidentals
In most cases, a sharp raises the pitch of a note one semitone while a flat lowers it a semitone. A natural is used to cancel the effect of a flat or sharp. This system of accidentals operates in conjunction with the key signature, whose effect continues throughout an entire piece, unless canceled by another key signature. An accidental can also be used to cancel or reinstate the flats or sharps of the key signature.
Since about 1700, accidentals have been understood to continue for the remainder of the measure in which they occur, so that a subsequent note on the same staff position is still affected by that accidental, unless marked as an accidental on its own. Notes on other staff positions, including those an octave away, are unaffected. Once a barline is passed, the effect of the accidental ends, except when a note affected by an accidental is tied to the same note across a barline. Sight reading music at speed can be mentally (and physically) taxing, so where an editor or engraver sees a possible opportunity for confusion, a courtesy or cautionary accidental may be placed by a note whose pitch is, strictly speaking, already given by the key signature. This accidental is usually within parentheses.
Full article ▸