Accidental

Altering a note

A sharp raises a note by a semitone: C becomes C♯, F becomes F♯. A flat lowers it by a semitone: B becomes B♭, D becomes D♭. A natural cancels an earlier alteration and restores the natural note. (German names add the syllable -is or -es instead: cis, des. The exceptions are h → b, e → es and a → as.)

Key signature and accidentals

If sharps or flats come right after the clef, they apply to the whole piece and to every matching note of the whole line. That is the key. A single accidental in the middle of the piece, on the other hand, applies only until the end of the bar.

The flats of a key signature appear in the order B♭, E♭, A♭, D♭, G♭, C♭, F♭; the sharps follow the opposite series F♯, C♯, G♯, D♯, A♯, E♯, B♯ (see Sharp). Both series are steps of a fifth, which is exactly what the circle of fifths shows. How to read the key from the key signature is explained on the page Key.

Accidentals in the score

In these pieces you see key signature and accidentals in practice.

Piano

• Menuett G-Dur Christian Petzold, BWV Anh. 114, from the Notebook for Anna Magdalena Bach · piano · 1 page

  One sharp in the key signature (F♯), 3/4. In the second part (from bar 17) accidentals appear, for example a ♯ before C in bar 20.

Guitar

• Lektion Nr. 5 Fernando Sor, op. 60 No. 5 · guitar · 1 page

  The beginning has no key signature. In bar 17, after the repeat sign, three sharps appear in the middle of the staff; the middle section is in A major.

Common mistakes

• Forgetting the key signature at the start of the line: The key signature applies to every matching note of the whole line, not only the first.
• Carrying an accidental across the barline: An accidental applies only until the end of the bar.
• Putting the sign after the note: In text you write “B♭” with the letter first, but in the score the sign is written before the notehead.