Book 3 introduces the concepts of key, key signature, scales, triads, tones (whole steps), and semitones (half steps) in a novel and exciting way. Each key is a group of characters or objects with note-names (i.e. a band, a birthday party, a clothes-line with garments). Certain notes belong, while all other notes (accidentals) are outsiders. Transposition is a natural outcome of this concept, with a tune moving from one group to another. The child...