Key Signature

The key signature is a group of sharps or flats placed at the beginning of each staff (after the clef) that applies to all notes of the indicated pitches throughout the piece. Rather than writing each accidental every time the note appears, the key signature establishes the prevailing tonality.

A key signature with one sharp (F#) indicates G major or E minor. Two sharps (F#, C#) indicates D major or B minor. Each additional sharp adds a new pitch to be raised. Similarly, flat key signatures: one flat (B♭) indicates F major or D minor; two flats (B♭, E♭) indicates B♭ major or G minor.

The key signature is a notational shortcut. Rather than writing every accidental on every relevant note, the composer establishes the prevailing tonality at the beginning of each staff. Notes within the indicated pitches are automatically raised or lowered until cancelled by a natural sign or by a new key signature.

English, descriptive — the ‘signature’ of the key.

Read the key signature carefully. Every note of the indicated pitches is automatically affected — F# in G major means every F is raised, regardless of octave. Forgotten key signature notes are one of the most common reading errors.