Sharps, flats and naturals

Seven letter names cover twelve pitches per octave. Accidentals cover the gap.

• Sharp (♯) — raise the note by one semitone.
• Flat (♭) — lower it by one semitone.
• Natural (♮) — cancel a previous sharp or flat, returning to the plain letter.

A semitone is the smallest step in standard Western tuning: on a piano, the very next key, black or white.

Enharmonics: two names, one pitch

C♯ and D♭ are the same key on a piano. So are F♯ and G♭, A♯ and B♭. These are enharmonic spellings.

Which name is correct depends on context, not preference. In D major the note is C♯, because D major's scale needs one of each letter — C♯ and D, never D♭ and D. Spelling follows the scale, and getting it wrong makes music harder to read even though it sounds identical.

Two things that surprise people: E♯ is F, and C♭ is B. There is no black key between E and F, or between B and C, but the names still exist and are used when the key demands them.

How long an accidental lasts

This catches everyone once.

An accidental applies to that note, in that octave, for the rest of the bar. Not just the note it sits in front of.

So if bar 5 has an F♯ on beat one, every subsequent F in that octave in bar 5 is also sharp — even without a symbol. The bar line cancels it. Bar 6 starts fresh.

Editors often add a courtesy accidental in brackets in the next bar to remove any doubt. It changes nothing; it just reassures the reader.

Accidentals vs key signatures

A key signature at the start of the staff applies to every octave, for the whole piece, until it changes.

An accidental in the music applies to one octave, for one bar.

If a piece in G major (F♯ in the signature) needs a plain F for one bar, it gets a natural sign. That natural lasts to the end of the bar, and then the key signature takes over again.

Double sharps and double flats

Rarely, you will see 𝄪 (double sharp) or ♭♭ (double flat), raising or lowering by two semitones. F𝄪 sounds like G. They exist for the same reason as everything else here: keeping one letter per scale degree so the music reads correctly.