Key Signatures

In principle, any piece can be written with any key signature, using accidentals to correct any notes where it shouldn't apply. The purpose of the key signature is to minimize the number of such accidentals required to notate the music. The sequence of sharps or flats in key signatures is generally rigid in modern music notation. For example, if a key signature has only one sharp, it must be an F sharp.

The effect of a key signature continues throughout a piece or movement, unless explicitly canceled by another key signature. For example, if a five-sharp key signature is placed at the beginning of a piece, every A in the piece in any octave will be played as A sharp, unless preceded by an accidental.

• This Key Signature circle is sometimes called the circle or cycle of fifths or fourths.
• A sharp or flat is called an accidental.
• Accidentals are not mixed in the major or minor key signatures.
• Each successive key signature around the circle includes the previous key signature's accidentals.
• The last sharp in a key signature is the letter right before the name of the major key.

  Example: The last sharp in G major key signature is F. (A B C D E F G A)

  The last sharp in E major key signature is D. (A B C D E F G A B)

• The second to last flat for all flat keys except F is the key.
• The order of Sharps move in perfect fifths. The order of Flats in move in perfect fourths.
• The primary chords, the I, IV, and V chords of major keys are the chords to the left and right of the key signature. The IV chord is to the left along the circle and the V chord is to the right along the circle.