Accidentals

The symbols are ♯ (sharp), ♭ (flat) and ♮ (natural). A double sharp raises a written note by two semitones; a double flat lowers it by two. The name still follows the letter on the staff: E sharp uses the F key, and C flat uses the B key on a modern equal-tempered piano. The spelling tells you how the note functions, not just where your finger lands.

In modern staff notation, an accidental normally applies to that note name in the same octave for the rest of the measure. At the next barline, the key signature takes over again unless a new accidental appears. For example, in a key signature with F sharp, an F natural inside one measure changes later Fs at that same staff position in that measure. The next measure returns to F sharp.

A tie across a barline keeps the altered pitch for the tied note. A newly attacked F later in the new measure follows the key signature unless the score marks otherwise. Courtesy accidentals, sometimes in parentheses, often remind the player what applies after a confusing change.

A key signature sits just after the clef and normally applies throughout the music, across octaves, until the signature changes. A local accidental appears beside a note and temporarily overrides that default. Read the key signature first, then check for a local sign immediately before the note.

Imagine one measure containing F sharp, another F at the same height, and then a barline followed by F. Say each pitch before playing: F sharp, F sharp, and then whatever the key signature requires. Repeat with F natural in a key whose signature contains F sharp. Reading Music puts pitch signs in the larger reading sequence.