Sharps, flats and naturals

A sharp raises a note by one half step, the distance from a key to its nearest neighbour.

Half steps on the keyboard

Seven letter names are not enough for the twelve different keys in each octave of a piano. The missing names come from accidentals, small signs written in front of a note. To understand them, start with the half step, the smallest distance in Western notation: from any key to the very next key, black or white. Most white keys have a black key between them, so they are two half steps, or one whole step, apart. Two pairs, E to F and B to C, have no black key between them. They are already a half step apart.

Three common signs

A sharp (♯) raises a note by a half step. A flat (♭) lowers it by a half step. A natural (♮) cancels an earlier sharp or flat and returns the note to its plain white-key form. The sign is always written to the left of the note, on the same line or space as the notehead, even though we say the name the other way round: we write ♯ then the note but say "F sharp". The black key just right of F is F♯; the black key just left of G is G♭. They are the same key with two spellings.

Enharmonic spellings

Two names for one sound are called enharmonic spellings. C♯ and D♭ are enharmonic, and so are D♯ and E♭, F♯ and G♭, G♯ and A♭, A♯ and B♭. The rule even reaches white keys: E♯ is the same key as F, and B♯ the same as C, because there is no black key in between. Which spelling a composer chooses depends on the key and on how the melody moves, a subject for the scales course. For reading, the point is simpler: find the letter first, then move one key right for a sharp or one key left for a flat.

Two rarer signs exist as well. A double sharp (𝄪) raises a note by two half steps, and a double flat (𝄫) lowers it by two. They appear in music with many sharps or flats in the key, and you can leave them for later.

An accidental lasts for the bar

An accidental applies to the note it is attached to and to every later note on the same line or space until the next bar line. After the bar line it is forgotten, unless the note is tied across. So if a bar contains F♯ followed by two more Fs without signs, all three are F♯. To return to F inside the same bar, the writer must add a natural. Many editions print a courtesy accidental in brackets in the next bar as a reminder, even though it is not strictly needed. This is why accidentals are sometimes described as temporary signs, as opposed to the key signature at the start of each line that lasts for the whole piece.