A history of the development of harmony in Western music from 500 BC to 1600, from Pythagoras to Josquin Desprez.
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Harmony developed in the early Middle Ages. Most cultures preferred monody, but in Europe, the composers and choirmasters realized that singers had different ranges, and thus it was easier for some singers to sing higher tones, while others were more comfortable singing lower tones. The result was hauntingly beautiful - and so harmony spread from the monasteries and cathedrals to the University of Paris, and over the years different sorts of harmony and different rules developed. It's a fascinating story - and now it's used in just about every type of musicial piece, from the music of the Appalachian mountains to the harmonies used in folk and rock music to complex operatic octets.
What exactly is harmony? This book focuses primarily on harmony in medieval and Renaissance music, but there is so much more to that word. We speak of harmony among individual human beings, among cultures, among nations, etc. Visual artists combine different colors in order to create a beautiful blend of hues and shades that appeal to the emotions in a positive way . . . [T]he first use of the word that we know of . . . seems to have been applied to music.