This is an eminently practical system for creating music, and none of the masterworks of late 19th-or 20th-century music -- that of Chopin, Brahms, or Debussy, for example -- could possibly have been written without it. But to European musicians before the 19th century, suggestions that it should be used were taken as a call to battle. Keyboard instruments could play harmonies of magical, uncorrupted sweetness in one moment -- and of uncompromising harshness the next, and that was that.

The conflict over whether or not to eliminate those sour notes is the heart of this book, as even such great thinkers as Rene Descartes and Johannes Kepler, not to mention kings and queens, held on to the ancient mathematical principles of Pythagoras and the "geometry of God, " while modernists fought passionately for temperament. This is a little gem of a book, telling a story that encompasses social history, religion, philosophy, science, and musical evolution, as well as some of music's most illustrious names, during a period when Europe was struggling to give birth to the modern age.