|Look up accidental in Wiktionary, the free dictionary.|
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. In the measure in which it appears, an accidental sign raises or lowers the following notes from their normal pitch, ignoring sharps or flats (or their absence) in the key signature. A note is usually raised or lowered by a semitone, although microtonal music may use "fractional" accidental signs. 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.
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. In this case subsequent notes at the same staff position in the second bar are not affected by the accidental carried through with the tied note. 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.
Though this tradition is still in use particularly in tonal music, it may be cumbersome in music that features frequent accidentals, as is often the case in non-tonal music. As a result, an alternate system of note-for-note accidentals has been adopted with the aim of reducing the number of accidentals required to notate a measure. The system is as follows:
- An accidental carries through the measure affecting both the note it immediately precedes and any following notes on the same line or space in the measure.
- Accidentals do not affect the same note of a different octave, unless indicated by a key signature.
- Accidentals are not repeated on tied notes unless the tie goes from line to line or page to page.
- Accidentals are not repeated for repeated notes unless one or more different pitches [or rests] intervene.
- If a sharp or flat pitch is followed directly by its natural form, a natural is used.
- Cautionary accidentals or naturals (in parentheses) may be used to clarify ambiguities, but should be held to a minimum.
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.
Note that in a few cases the accidental might change the note by more than a semitone: for example, if a G sharp is followed in the same measure by a G flat, the flat sign on the latter note means it will be two semitones lower than if no accidental were present. Thus, the effect of the accidental has to be understood in relation to the "natural" meaning of the note's staff position. For the sake of clarity, some composers put a natural in front of the accidental. Thus, if in this example the composer actually wanted the note a semitone lower than G-natural, he might put first a natural sign to cancel the previous G-sharp, then the flat. However, under most contexts, an F-sharp could be used instead.
Double accidentals raise or lower the pitch of a note by two semitones, an innovation developed as early as 1615. This applies to the written note, ignoring key signature. An F with a double sharp applied raises it a whole step so it is enharmonically equivalent to a G. Usage varies on how to notate the situation in which a note with a double sharp is followed in the same measure by a note with a single sharp: some publications simply use the single accidental for the latter note, whereas others use a combination of a natural and a sharp, with the natural being understood to apply to only the second sharp.
The double accidental with respect to a specific key signature, raises or lowers the notes containing a sharp or flat by a half step. For example, when in the key of C-sharp minor or E major, F,C,G, and D contain a sharp; adding a double accidental (double sharp) to F for example in this case would only raise the already sharp containing note F one half step or semitone, creating G natural, respectively. Conversely, if a double sharp were added to any other note not containing a sharp or flat as indicated by the key signature then the note will be raised two semitones or a whole step with respect to the chromatic scale. For example, in the aforementioned key signature any note that is not F, C, G, and D will be raised by a whole step or two semitones instead of one, so an A double sharp raises the note A to the enharmonic equivalent of B.
Courtesy accidentals 
Although a barline is nowadays understood to cancel the effect of an accidental (except for a tied note), often publishers will use a courtesy accidental (also referred to as a cautionary accidental or a reminder accidental) as a reminder of the correct pitch if the same note occurs in the following measure. This usage varies, although a few situations are construed to require a courtesy accidental, such as
- when the first note of a measure had an accidental applied to it in the previous measure
- after a tie carries an accidental across a barline, when the same note appears again in the subsequent measure.
Other uses are inconsistently applied.
Courtesy accidentals are sometimes enclosed in parentheses to emphasize their nature as reminders.
Microtonal notation 
Composers of microtonal music have developed a number of notations for indicating the various pitches outside of standard notation. One such system for notating quarter tones, used by the Czech Alois Hába and other composers, is shown on the right.
In the 19th and beginning 20th century, when Turkish musicians switched from their traditional notation systems — which were not staff-based — to the European staff-based system, they created a refinement to the European accidental system in order to be able to notate Turkish scales which make use of intervals smaller than the tempered semitone. There are several such systems which vary as to the division of the octave they presuppose or merely the graphical shape of the accidentals. The most widely used system (created by Rauf Yekta Bey) uses a system of 4 sharps (roughly +25 cents, +75 cents, +125 cents and +175 cents) and 4 flats (roughly −25 cents, −75 cents, −125 cents and −175 cents), none of which correspond to the tempered sharp and flat. They presuppose a Pythagorean division of the octave taking the Pythagorean comma (about an 8th of the tempered tone, actually closer to 24 cents, defined as the difference between 7 octaves and 12 just-intonation fifths) as the basic interval. The Turkish systems have also been adopted by some Arab musicians.
Ben Johnston created a system of notation for pieces in just intonation where the unmarked C, F, and G major chords are just major chords (4:5:6) and accidentals are used to create just tuning in other keys. Between 2000 and 2003, Wolfgang von Schweinitz and Marc Sabat developed The Extended Helmholtz-Ellis JI Pitch Notation, a modern adaptation and extension of the notation principles first used by Hermann von Helmholtz, Arthur von Oettingen and Alexander John Ellis which is rapidly becoming adopted by musicians working in extended Just Intonation (for more details, see the Wikipedia article on Just Intonation).
History of notation of accidentals 
The three principal symbols indicating whether a note should be raised or lowered in pitch are derived from variations of the small letter b: the sharp (♯) and natural (♮) signs from the square "b quadratum", and the flat sign (♭) from the round "b rotundum".
In the early days of European music notation (4-line staff Gregorian chant manuscripts), only the note B could be altered (i.e. have an accidental applied to it): it could be flattened, thus moving from the hexachordum durum (i.e. the hard hexachord: G-A-B-C-D-E) where it is natural, to the hexachordum molle (i.e. the soft hexachord: F-G-A-B♭-C-D) where it is flat; the note B is not present in the third hexachord hexachordum naturale (i.e. the natural hexachord: C-D-E-F-G-A).
This long use of B as the only altered note incidentally helps explain some notational peculiarities:
- the flat sign ♭ actually derives from a round b, signifying the B of the soft hexachord, that is, B flat (hence the name of the flat sign in French "bémol" from medieval French "bé mol" — modern French "bé mou" — or "soft b") and originally meant only B♭;
- both the natural sign ♮ and the sharp ♯ derive from a square b, signifying the B of the hard hexachord, that is, B natural (hence the name of the natural sign in French "bécarre" from medieval French "bé carre", earlier "bé quarre" — modern French "bé carré" — or "square b") and originally meant only B natural.
In the same way, in German music notation the letter B designates B flat while the letter H, which is actually a deformation of a square B, designates B natural.
As polyphony became more complex, notes other than B needed to be altered in order to avoid undesirable harmonic or melodic intervals (especially the augmented 4th, or tritone, that music theory writers referred to as "diabolus in musica", i.e. "the devil in music"). The first sharp in use was F♯, then came the second flat E♭, then C♯, G♯, etc.; by the 16th century B♭, E♭, A♭, D♭, G♭ and F♯, C♯, G♯, D♯ and A♯ were all in use to a greater or lesser extent.
However, those accidentals were often not notated in vocal part-books (but the correct pitches were always notated in tablature). The notational practice of not marking implied accidentals, leaving them to be supplied by the performer instead, was called musica ficta (i.e. "feigned music").
Strictly speaking the medieval signs ♮ and ♭ indicate that the melody is progressing inside a (fictive) hexachord of which the signed note is the mi or the fa respectively. That means they refer to a group of notes around the marked note, rather than indicating that the note itself is necessarily an accidental. Occasionally it is possible to see a mi-sign (♮) associated with, for example, a D. This could mean that the D is simply a D, but the note above E is now fa, i.e. it is one that is actually flattened to E flat (the 'accidental' in modern parlance).
See also 
- Alves, William (2008). Music of the peoples of the world, p.86. ISBN 978-0-495-50384-2.
- Palmieri, Robert, and Margaret W. Palmieri. "Ebonies", Piano: An Encyclopedia, p.118. New York: Routledge, 2003. ISBN 0-415-93796-5.
"The ebonies are the black keys of a piano, called variously sharps or accidentals,..."
"The ivories are the white keys of the piano (also called naturals), ..."
- Stone, Kurt. Music Notation in the Twentieth Century: A Practical Guidebook,[page needed]. New York: W. W. Norton & Co., 1980.
- Manoff, T: "The Music Kit Workbook", Fourth Edition, page 47. Norton, 2001.
- Benward & Saker: Music in Theory and Practice, Seventh edition, Vol 1, p.6. McGraw-Hill, 2003.
"Double Sharp ()—raises the pitch two half steps. Double Flat ()—lowers the pitch two half steps."
- Marshall, Wolf (2008). Stuff! Good Guitar Players Should Know: An A-Z Guide to Getting Better, p.59. ISBN 9781423430087.
- Niecks, Frederick. The Flat, Sharp, and Natural. A Historical Sketch. Proceedings of the Musical Association, 16th Sess., (1889 - 1890), pp. 79-100.(JSTOR)