Book excerpt: (Explained). The circle of fifths is a familiar tool known by many musicians. Although this device usually receives nothign more than a brief explanation in most music theory books, the circle illustrates the foundation that organizes much of Western tonal music and is therefore essential to grasp. With the novice musician in mind, author Dan Maske expounds on the nature, nuances and applications of the circle of fifths throughout this book, exploring topics such as: intervals, keys and key signatures, scales, chords and chord progressions, and more.