In music notation, an accidental is a sharp, flat, natural, double sharp, double flat, or double natural sign to the left of the note-head of a particular note. It indicates that the note following it should be changed by a half step or whole step.

An accidental changes a note the same way that a sharp, flat, or natural in the key signature will, but with two significant differences. First, the change remains in effect only for the current measure. Second, the change only applies to that specific note, in that specific octave -- if a high C is changed to a C-sharp, then a middle C in the same measure remains unchanged unless given its own accidental.

A composer may repeat an accidental in parentheses as a reminder. This may be done either in the same measure to remind that the accidental is still in force, or in the following measure to remind that the key signature is again in effect.

A small additional note: In music, an accidental in "in effect" until the end of the measure. Thus, if the first B in the measure is an accidental B-flat, then any other B's in the measure are also flat.

From a compositional point of view, the accidentals are there to allow you to use notes that are not properly "in" the key you're writing in. So, while all B's in the key of C are natural, you could slip in an accidental if you really wanted a B-flat, just this once. (Well, for the rest of the measure. Then again, if a measure has three B's, and the first is an accidental flat, but the second is an accidental natural, then, well, the third is natural too. Freaky, huh?)

I've always thought about the relationship between key signature notes, and accidentals rather like the philosophical distinction between necessary and accidental.

The former--the necessary--is part of the fabric of the universe, and must occur; the latter--the accidental--is not part of the fabric of the universe, and is just an accident.

This doesn't really hold up too well, but I have always found it amusing. And I rarely share it with my students, as they are with me for music, not philosophy--or humor.

In music, an accidental is a sharp, flat, or natural that is not in the key signature. It affects the note directly to its right and stays in effect throughout the entire measure unless otherwise noted (haha, pun!).

The interesting thing about accidentals is which ones a composer chooses to use. For every note there are possible enharmonic spellings, i.e. a pitch can be written in different ways but ultimately sounds the same. For example, A# is the same as Bb, and E natural is the same as Fb. Therefore, when a composer alters a pitch, he or she must choose which note to write it as.

Traditionally, the note written dictates its resolution.* Sharps resolve up and flats resolve down; naturals resolve either way depending on whether their notes were originally sharped or flatted. In short, lowered notes resolve down and raised notes resolve up. So if a composer writes an A#, the implication is a movement towards B. However, if he writes Bb, which sounds the same to the ear, the implication is a movement towards A.

A good example of this is the case of German sixth chords used in a major key. Augmented sixth chords are predominant in nature, meaning they lead to the V chord. In order to avoid parallel motion, these chords generally progress to a second-inversion tonic chord followed by a dominant chord (i64 - V). Normally, in minor, Gr6 chords are spelled as scale degree 1, b3, #4, and b6. This works because in the tonic chord, 3 is still flat. However, in major, they are often spelled as 1, #2, #4, and b6. This is because b3 is no longer a common tone between Gr6 and i64. Writing b3 in the Gr6 chord implies movement towards 2, but there is no 2 in a tonic chord. Instead, the b3 moves up to natural 3, so writing #2 is more appropriate because it implies the upwards resolution.

If you're not familiar with some of the terms in the previous paragraph, some write-ups you might find helpful are Augmented 6th chord and Degrees of the Scale. Feel free to msg me with any questions as well.

*rp has kindly pointed out that the way I stated this is backwards: the resolution dictates the accidental. So if C# is going to C natural, the composer would write Db instead. I explained it the way I did because that's how theorists view it: a Db would imply movement towards C; a C#, movement towards D. Really it is not the accidental that decides where the chord is going, but the resolution that decides how the accidental was written. I hope that clarifies things.

Ac`ci*den"tal (#), a. [Cf. F. accidentel, earlier accidental.]


Happening by chance, or unexpectedly; taking place not according to the usual course of things; casual; fortuitous; as, an accidental visit.


Nonessential; not necessary belonging; incidental; as, are accidental to a play.

Accidental chords Mus., those which contain one or more tones foreign to their proper harmony. -- Accidental colors Opt., colors depending on the hypersensibility of the retina of the eye for complementary colors. They are purely subjective sensations of color which often result from the contemplation of actually colored bodies. -- Accidental point Persp., the point in which a right line, drawn from the eye, parallel to a given right line, cuts the perspective plane; so called to distinguish it from the principal point, or point of view, where a line drawn from the eye perpendicular to the perspective plane meets this plane. -- Accidental lights Paint., secondary lights; effects of light other than ordinary daylight, such as the rays of the sun darting through a cloud, or between the leaves of trees; the effect of moonlight, candlelight, or burning bodies.


Syn. -- Casual; fortuitous; contingent; occasional; adventitious. -- Accidental, Incidental, Casual, Fortuitous, Contingent. We speak of a thing as accidental when it falls out as by chance, and not in the regular course of things; as, an accidental meeting, an accidental advantage, etc. We call a thing incidental when it falls, as it were, into some regular course of things, but is secondary, and forms no essential part thereof; as, an incremental remark, an incidental evil, an incidental benefit. We speak of a thing as casual, when it falls out or happens, as it were, by mere chance, without being prearranged or premeditated; as, a casual remark or encounter; a casual observer. An idea of the unimportant is attached to what is casual. Fortuitous is applied to what occurs without any known cause, and in opposition to what has been foreseen; as, a fortuitous concourse of atoms. We call a thing contingent when it is such that, considered in itself, it may or may not happen, but is dependent for its existence on something else; as, the time of my coming will be contingent on intelligence yet to be received.


© Webster 1913.

Ac`ci*den"tal (#), n.


A property which is not essential; a nonessential; anything happening accidentally.

He conceived it just that accidentals . . . should sink with the substance of the accusation. Fuller.

2. pl. Paint.

Those fortuitous effects produced by luminous rays falling on certain objects so that some parts stand forth in abnormal brightness and other parts are cast into a deep shadow.

3. Mus.

A sharp, flat, or natural, occurring not at the commencement of a piece of music as the signature, but before a particular note.


© Webster 1913.

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