From 《The Music of Man》 (7)

The circle of fifth is a human deduction, not a natural phenomenon. Nature always has its loose ends, elements that appear to our minds as mistakes, as if they simply should not happen. In our arrogance we feel that we should offer nature a correction, squaring the circle. The beauty of nature is that there is always an element that allows for mystery, for development or evolution. So it is with the circle of fifths, for when you come back to the note with which you started, providing the fifths have all been perfectly tuned, you find that this note has gone a little sharp. It is one of the mysteries of nature, as the Chinese knew by observation. We had to wait for Pythagoras to establish the precise mathematics of the difference, and it is now known as the Pythagoras to establish the precise mathematics of the difference, and it is now known as the Pythagorean Comma. Its existence is an important aspect of the difference between Western music and that of much of the rest of the world --- our music has always been based on pure or natural intervals (at least until this century). As we shall see, the rise of the keyboard instruments --- the organ, harpsichord and piano --- brought on a crisis in tuning precipitated by the conflict between pure intervals in one key and those in another. As with so much else in Western life, we adjusted the tuning to an uncomfortable compromise, a homage to the keyboard with which the voice and the string player are never totally comfortable.