An accidental is a sign placed in front of a note that raises, lowers, or cancels its pitch for the rest of that measure. The three common accidentals are the sharp, which raises the note a half step, the flat, which lowers it a half step, and the natural, which cancels a prior sharp or flat and restores the unaltered note. Accidentals are how music steps briefly outside its key without rewriting anything at the front of the staff. Here is what each sign means, how long it lasts, how it differs from the key signature, and why reading it correctly is what lets you play the right pitch.
Sharps, flats, and naturals
A sharp raises a note a half step, a flat lowers it a half step, and a natural cancels a prior sharp or flat to restore the unaltered note. Those are the three accidentals you meet constantly. The sharp sign (a small crosshatch) sits just to the left of the notehead and pushes it up to the next key on the piano; the flat sign (a small lowercase b) pushes it down. The natural sign undoes either one, returning the note to the plain letter pitch with no alteration, which is why it most often appears to correct a note the key signature or an earlier accidental had already changed. Two rarer signs round out the family: the double sharp raises a note two half steps (a whole step), and the double flat lowers it two half steps. You will not see them often, but they exist so that a note can keep its correct letter name in keys where a single sharp or flat would not be enough.
How long an accidental lasts
An accidental applies from where it appears through the end of that measure, in that octave, and then the barline cancels it. So if you sharp an F on beat one, every F in the same octave for the rest of that measure is also sharp, with no need to write the sign again. The moment the barline arrives, the alteration is gone and the note returns to whatever the key signature says. This trips up beginners in two opposite ways. The first mistake is thinking an accidental affects only the single note it sits in front of, and then playing the next matching note in the measure without the alteration. The second is thinking it holds for the whole piece, and then carrying a sharp across the barline where it no longer applies. It does neither: its reach is exactly the rest of the current measure, in the same octave, and no further.
Accidentals vs the key signature
The key signature sets the sharps or flats for the whole piece; an accidental is a one-off change against that backdrop. The key signature, stated once after the clef, is the standing rule: it tells you which notes are consistently raised or lowered every time they appear. An accidental is the local exception to that rule, either a note pushed outside the key for a measure, or a temporary cancellation of a sharp or flat the key signature would otherwise apply. In a key with an F-sharp in the signature, writing a natural in front of an F makes it an F-natural for the rest of that measure, overriding the key. If you want the fuller picture of how the standing sharps and flats are chosen and read, see what is a key signature.
Why the same key can be a sharp or a flat
The same black key on the piano can be named as a sharp of the note below it or a flat of the note above it, and the correct spelling depends on the key and the voice leading. The pitch between F and G, for instance, is F-sharp when you think of it as a raised F and G-flat when you think of it as a lowered G. They sound identical, but they are not interchangeable on the page: the key you are in, and the direction the melody is moving, decide which name keeps the music readable and the letter sequence intact. Choosing F-sharp in a sharp key and G-flat in a flat key is not a matter of taste but of correct notation. This pair of names for one pitch is what musicians call enharmonic spelling, and we cover it in full in enharmonic notes explained. Because the distance involved is a half step, it also helps to understand how intervals are measured, which is the subject of what is a musical interval.
Why accidentals matter
Accidentals let music step outside its key without rewriting the key signature, and reading them correctly is essential to playing the right pitch. Almost every real piece borrows notes from outside its key at some point, and accidentals are how those notes get onto the page cleanly, marked exactly where they happen and canceled at the next barline. Miss one, or misjudge how far it reaches, and you play the wrong note, so the ability to spot an accidental and track its scope is a core reading skill. If you are still building that skill, start with how to read sheet music, and keep the music notation glossary handy for the surrounding terms. If you would rather have the notation handled for you, Songscription notates accidentals correctly from your recording and picks a sensible key, so the sharps, flats, and naturals land where they belong without you placing them by hand.
Frequently Asked Questions
What is an accidental in music?
An accidental is a sign placed in front of a note that raises, lowers, or cancels its pitch for the rest of that measure. The three common accidentals are the sharp, which raises the note a half step, the flat, which lowers it a half step, and the natural, which cancels a prior sharp or flat and restores the unaltered note.
How long does an accidental last?
An accidental applies from where it appears through the end of that measure, and only in the same octave. Once the barline arrives, the accidental is canceled and the note returns to whatever the key signature says. A common beginner mistake is to think an accidental affects only the single note it sits in front of, or that it holds for the whole piece; it does neither.
What is the difference between an accidental and a key signature?
A key signature sets the sharps or flats that apply to the whole piece, stated once at the start of each staff. An accidental is a one-off change against that backdrop: a note pushed outside the key for a measure, or a temporary cancellation of a sharp or flat the key signature would otherwise apply. The key signature is the standing rule; an accidental is a local exception.
What is a natural sign?
A natural sign cancels a prior sharp or flat and restores the note to its unaltered pitch for the rest of the measure. It is used to override the key signature or an earlier accidental, so a note that would otherwise be sharp or flat is played as the plain white-key pitch instead.
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