Accidentals: sharp, flat, natural – free music theory course

Between two neighbouring piano keys (white or black) there is a semitone (or half step), the smallest distance in Western music. Accidentals raise or lower a note by one or two semitones.

Sign	Name	Effect
♯	sharp	raises the note by a semitone
♭	flat	lowers the note by a semitone
♮	natural	cancels an accidental: back to the "natural" note
𝄪	double sharp	raises by two semitones (a whole tone)
𝄫	double flat	lowers by two semitones

On the keyboard, F♯ is the key immediately to the right of F (a black key); B♭ is the key immediately to the left of B. Careful: the neighbouring key is not always black. There is no black key between E and F, or between B and C. So E♯ is the white key F, and C♭ is the white key B!

In writing

We say "F sharp" (note, then accidental) but we write the sign before the note, on the same line or space, so that the eye sees it before playing.

M:4/4
L:1/4
Q:1/4=80
K:C
F ^F G2 | B _B A2 | ^F F =F2 | ^^F2 __B2 |]

Listen to bar 3: the second F is still sharp, although no sign is written in front of it. The natural sign then restores F natural.

How long does an accidental last?

An accidental written in front of a note lasts until the end of the bar, for every note at the same pitch.
It only applies to notes in the same octave (an F♯ high up does not sharpen the left hand's F).
It is cancelled by the bar line, unless the note is tied across the bar line.
Accidentals in the key signature (at the start of every line) apply to the whole piece and every octave — we will study them with scales.

Courtesy (cautionary) accidentals: editors often add a reminder natural, sometimes in brackets, in the bar following an accidental, to remind you that the bar line cancelled it. It changes nothing; it prevents mistakes.

Common mistake: forgetting that an accidental holds for the whole bar. When sight-reading, keep every sharp or flat you meet "in memory" until the next bar line.